Dimage Scan Dual Scanner
Original Review Date: August 24, 1999
|Inexpensive "personal" film scanner|
|2438 dpi resolution (24.5 meg file from 35mm neg)|
|8 bits per channel (Dmax not specified)|
|High-speed SCSI interface|
|Software accommodates beginners AND experts|
|Optional APS adapter|
Minolta is a company with long experience in the world of film, and extensive digital expertise that has so far been applied primarily in the areas of office electronics and imaging (copiers & printers). Recently though, they've been making significant waves in the digital camera and scanner markets, with their highly capable (and expandable!) Dimage EX 1500 Zoom digital camera, and a whole line of film scanners covering everything from APS to 35mm, to medium-format photography. We've previously reviewed the Dimage Scan Dual (35mm and APS film formats), and the Dimage Scan Multi (multi-format, from 8mm movie film to 6x9 cm medium-format). With this review of the Dimage Scan Dual, the "personal" model in Minolta's lineup, we complete our coverage of their scanner lineup. (At least until they come up with yet another one!)
The Minolta Dimage Scan Dual film scanner is aimed at the "personal" scanner market, and fits well within that market, with a very affordable price, excellent resolution, and good control software. With its APS adapter, it provides a good solution for scanning that format as well, including the ability to "batch scan" an entire roll without user intervention. - More on this later.
"High Points" Overview
- 2438 dpi resolution
- 8-bit digitization
- User interface accommodates both beginners and experienced users
- "Preview" function can pre-scan entire APS film roll
- "Batch" scanning can scan entire APS film roll at any resolution
- Cold-cathode light source for long bulb life
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The Dimage Scan Dual is a desktop device about the size of a hefty novel standing on edge. (The long side down.) It measures 3.6 x 6.3 x 10.7 inches (90.5 x 160.5 x 272 mm), and weighs about 4.4 pounds (2 kg). Interface to the host computer is via a high-speed SCSI-2 interface, meaning you'll need to have such a port installed in your computer to use it. (Macs typically come equipped with SCSI connections: On a Windows machine, you'll need to have an interface card installed. Appropriate cards range from $100 to $300 in price. The manual lists a number of Adaptec SCSI cards from the 1500 and 2900 series that are suitable. The only restriction seems to be that the 1500-series boards don't work with NEC PC98xx computers.) We've seen some resellers offering packages with a SCSI card "bundled" with the unit, but more often have seen just the scanner itself being offered. The standard unit can scan 35mm negatives or slides, in either black and white or color. An optional APS adapter is available for scanning that film type.
The software CD shipped with the unit supports both Mac and Windows platforms. A Photoshop acquire plug-in is provided for the Mac, and TWAIN drivers for the PC, and Photoshop LE for both platforms provides very full-functioned image editing capabilities: Big kudos to Minolta for including such a powerful image-editing program with their scanner! (NOTE: Minolta specifies that the scanner requires either Windows '95 release 2 (OSR2), or Windows '98. If you're running Windows '95, be sure to check the revision level you have installed.)
Scanning resolution can be as high as 2438 dpi (apparently, a 2400-element CCD covering the width of a 35mm slide or negative, with a few unused pixels on either side). This produces maximum image sizes of 2336 x 3504 pixels for 35mm (24.5 megabytes), or 1776 x 2928 for APS (15.6 megabytes).
A note about scanner resolution, as compared to that of digital cameras: The 8.1 megapixel resolution of the Dimage Scan Dual is even higher than you might expect, when compared to the resolution of a digital camera. Because the scanner's CCD samples each pixel in all three red, green, and blue color channels, it's really equivalent to a digital camera with a 24 megapixel sensor and "striped" color filters. Thus, the first thing most people notice about images scanned from negatives and slides is the extraordinary level of detail captured. That said, the Dimage Scan Dual's scan resolution of 2438 dpi is at the top of the field for 35mm/APS "personal" scanners.
Another important scanning parameter is "bit depth," a measure of both color accuracy and the maximum density range the scanner can recognize. (8 bits per channel is good, 10 better, and 12 the best you'll commonly find in desktop scanners.) The Dimage Scan Dual captures 8 bits per pixel, while its "big brother" the Dimage Scan Speed captures 12. We found the 8-bit color depth sufficient for negatives and well-exposed slides, but the Scan Dual did have trouble with our extremely dense "Train" slide.
Scanner Optics & Light Path
Film scanners tend to take one of two approaches in their optical design, providing either fixed or adjustable focus. The Dimage Scan Dual employs fixed-focus optics. Given the extreme resolution of most film scanners, we're surprised that the lenses can be designed with enough depth of field to insure sharp focus in the face of minor variations in the film plane position. We're surprised, but the fixed-focus approach nonetheless seems to work quite well, as evidenced by the performance of the Dimage Scan Dual. The upside of fixed-focus designs of course, is that you don't have to worry about focusing, either in the form of twiddling a thumbwheel, or by waiting while the scanner adjusts its focus for every scan. In our testing, the Dimage Scan Dual produced sharp images every time, the sole exclusion being one orientation of our unusual "USAF 1951" resolution target, which is a glass slide with the pattern deposited on one side of it. With the pattern facing one way, we got sharp results, but decidedly blurry ones with it facing the other. We saw no evident focus deficiencies while scanning normal slides or negatives.
The Dimage Scan Dual uses a special fluorescent light source, producing strong spectral peaks in the red, green, and blue portions of the spectrum. We observed that this diffuse illumination source produced somewhat "softer" scans than some other scanners. The resulting scans had less of a razors-edge on fine detail, but were also much more forgiving of film defects and film grain. A good analogy (for those old darkroom aficionados out there) would be the difference between condenser and diffusion enlargers: The condenser optics tend to produce sharper images, but at the cost of greatly enhanced grain, while diffusion enlargers create a softer look. Note in this though, that while the scans produced by the Dimage Scan Dual have a somewhat "softer" appearance to them, they in fact appear to carry an extremely high level of detail, as evidenced by the results from our WG-18 (ISO-12233) resolution target scans. Another characteristic of the Dimage Scan Dual that impressed us was the complete absence of color "aliasing", wherein closely-spaced, high-contrast detail can cause flecks or streaks of color to appear that weren't in the original image. Unlike some scanners, the Dimage Scan Dual showed absolutely no tendency to produce artifacts of this sort.
The Dimage Scan Dual uses plastic slide- and filmstrip-holders to carry the film to the scanner: You first place the media to be scanned into the holder, then insert the holder into the scanner. The holders have detent notches on them that provide repeatable film positioning, and yet allow for manual advance of the film between frames. During scanning, the holder and film is moved past a fixed CCD array. The filmstrip holder can accommodate strips of 35mm film up to six frames in length, and the slide holder up to four slides. Both holders are reversible, a necessary feature for their use: Inserted into the scanner, you can access half of the total film frames by sliding the adapter in or out. To reach the remaining frames, you remove the adapter, flip it end for end, and reinsert it.
We found both the slide and film holders to be quite effective and easy to use.
The film adapter is hinged, but only to the extent that a plate flips up to
expose the recess into which the film is laid. (Unlike many "clamshell"
designs, the slot holding the film is a fixed structure.) The back pressure
plate then hinges back down and latches, clamping the film flat. This arrangement
did a particularly good job of handling curled or damaged film, regardless of
whether the film was curled side-to-side, or along its length. The film-holding
slot is about a half-millimeter wider than the film itself, doing a good job
of constraining the film position, yet still allowing minor adjustments to be
made for fine alignment relative to the limits of the scanning area. We did
find that the filmstrip holder crops the 35mm frame very slightly, about 3%
in both vertical and horizontal directions by our reckoning. (For some reason,
this appears to be a common characteristic of strip-film holders.)
The slide holder is also constructed of plastic, with four slots along the top edge into which the slides may be loaded. The edges of each slot set absolute limits for the horizontal position of the slide mount, but there's a bit more play (about a full millimeter side-to-side) with slides than is present in the filmstrip adapter. This is probably a good thing, as it allows you to correct for film misaligned in its mount: You can manually tweak the slides to achieve about two degrees of rotation in either direction, as needed. (Despite this looseness, we had no difficulty aligning slides square to the holder, as the edges of the "windows" in the holder provided good reference surfaces to align to, and simply "bottoming out" the slide in the slot yielded good alignment if the film was properly positioned in the slide mount.) The slide holder is also a little unusual in the way that the slides "float" between two sets of spring-loaded fingers. This seemed to do a good job of keeping the film plane well-centered about the point of optimum focus. The centering fingers gripped a particularly thick plastic-and-glass slide mount quite a bit more firmly than they did standard cardboard ones, but handled a wide range of mounts well.
Our one quibble with the Dimage Scan Dual's film handling (and a minor one at that) was that the slide holder didn't allow you to insert the slide all the way into the carrier in a single step: You had to push it in as far as possible from the top, then reach in from the sides with your fingers to tug it all the way down to it's final position. This left us a little nervous that we might inadvertently smudge the film with our fingers, although we never actually did so in practice.
Minolta shipped us the optional APS adapter along with the Dimage Scan Dual, so we got a chance to try it out as well. (NOTE that the APS adapter is an optional accessory, sold separately from the scanner itself.) This worked quite well, although as with other APS scanners we've used, there's what seems like an interminable period of whirring and clicking (actually about 20 seconds or so) before it begins an index scan: We assume this is necessary to count the number of frames in the roll or something. The APS adapter is a separate unit with a hatch on top that opens to reveal an opening to receive the APS film cartridge. With the film inside, the whole assembly is inserted into the front of the scanner. The APS adapter contains a small motor that advances the film between frames, and rewinds it into the cartridge when you're done scanning. Once a desired frame has been positioned in the opening on the side of the adapter, the 'Dual scans it by moving the entire adapter in and out to move the film past the scan head. The APS adapter seemed to work quite well, our only complaint that being that it took a long time to produce an index scan of the roll. (About 5 minutes for a 25-exposure roll!) As it turns out though, this is really a non-issue, since you probably got an index print with your roll of processed APS film anyway. Assuming you know which frames you want to scan, it's an easy matter to select the ones you want, prescan them, make whatever adjustments you'd like for each, and then have the scanner batch-scan them all, by control- or command-clicking to select those you're interested in before pressing the "Scan" button.
System Interface and Included Software
As mentioned earlier, the Dimage Scan Dual uses a SCSI-2 connection to the host computer, providing the high speed data transfer necessary to handle the large amounts of data the scanner can generate. No SCSI card is included with the unit, but Minolta lists several models of Adaptec cards that the unit can be used with. Adaptec is pretty much the standard for SCSI cards: You can find cheaper ones, but the Adaptec models are more likely to be compatible with a wide range of equipment. Note in particular, that some scanners, CD-ROM drives, and other equipment ships with low-cost SCSI cards included. In many cases, these are "dedicated" cards, that will only run the particular device they're shipped with. If you're buying a card to support the Dimage Scan Dual, take our advice and get a "name brand" Adaptec unit. The hassle you'll save will be more than worth it! (Also note that there appear to be "bundles" available which include a SCSI card along with the scanner: Check with your reseller to see what's available.)
Once connected to the computer, the Dimage Scan Dual is controlled through an excellent software interface that we'll describe in greater detail below. As noted earlier, the scanner-control software takes the form of standalone applications on both the Mac and PC, as well as a Photoshop plug-in on the Mac, and a TWAIN component on the PC. A particular strength of the Dimage software is the extent to which it provides powerful controls for experienced users, while at the same time offering a simple interface for novices.
A nice touch in the Dimage Scan Dual package was the inclusion of Adobe's Photoshop LE, for both Mac and Windows. Photoshop LE is a slightly trimmed-down version of the full Photoshop package, the primary omissions being support for color spaces other than RGB (such as CMYK, for commercial offset printing), and less in the way of color management. At one time, it was quite common to find Photoshop LE or even a full version of Photoshop bundled with many scanning devices. The combination of policy changes at Adobe (implemented in the form of radically higher prices to their bundling partners), and ever-tightening margins and declining retail prices in the scanner market have all but eliminated Photoshop from the "bundle" market. We applaud Minolta's inclusion of this program with the Dimage Scan Dual though: We suspect that many potential purchasers of the Scan Dual will be upgrading their imaging capability with the acquisition, and won't already have a copy of Photoshop. While trimmed-down somewhat from the capabilities of the full version, Photoshop LE is a dramatic step up from the "dumbed-down" interface and capabilities of Adobe's PhotoDeluxe, a much more common software bundle component these days. Don't get us wrong, PhotoDeluxe is an excellent program, but is clearly targeted at the casual user. Even at that though, we've long felt that removing key features such as the "levels" control is no gift to the end-user. While it may make the program easier to use, such simplification ultimately leaves users at a dead end, with nowhere to go as their skills and abilities improve. Photoshop LE is adequate to the needs of most semi-pro users, and will provide the full range of capabilities that most users will need to achieve the best results. Flame off for now, but repeated kudos to Minolta for taking the cost hit and including Photoshop LE with the scanner. One parting shot: You can't buy Photoshop LE, only the full version of Photoshop, which routinely sells for well over $500. Given that the LE version will be enough for the majority of users, the argument could be made that its inclusion in the Dimage Scan Dual bundle will save many people $500 or more. This fact alone is a significant differentiator for the Minolta's product.
Speeds and Feeds
As its name suggests, the Dimage Scan Dual is intended to be a fast scanner. In our testing, we found that it did indeed zip along pretty quickly. This appeared to be due partly to the basic mechanism and electronics (which moves the film and digests the data rapidly), and partly to the fixed-focus optics: When you tell the unit to begin scanning, there's no delay for focus adjustment before the scan starts. The unit does make one pass over the negative or slide first though, to determine an autoexposure level, a process that takes 4-5 seconds. Scanning throughput was quite good with the unit, helped by the flexible, easy-to-use software, but also by the fast scan times themselves. (We've only recently begun meauring preview and scan times, so won't have comparable numbers for many scanners we've previously tested. From this point on though, we'll be measuring these throughput-related timings on a routine basis...) Running the Dimage Scan Dual from our 333 MHz PowerMac G3, we measured the following scan times:
Preview w/o autoexposure:
Low res (~600dpi) full-frame scan w/o autoexposure:
Low res (~600dpi) full-frame scan w/autoexposure:
Full res (2438 dpi) full-frame scan w/o autoexposure:
Full res (2438 dpi) full-frame scan w/autoexposure:
Operation and User Interface
Other than the actual scans themselves, most of the story to be told about a film scanner has to do with the software that drives it, and to what extent the combination of hardware and software makes it easy to produce good-quality scans. Accordingly, we'll devote a sizable of this review to talking about the software that drives Minolta's Dimage family of scanners, and the Dimage Scan Dual in particular.
As noted several times already, we feel that Minolta has done a particularly good job of balancing capability with ease-of-use. This is a difficult equation to optimize, as the needs of "beginners" and "experts" can vary so widely. At the same time, the goal should be to provide a smooth gradation of capability, not introducing any abrupt hurdles to overcome as the users advance in their sophistication. Minolta has accomplished this difficult design goal by providing very basic, visually-oriented contrast/brightness adjustments for neophytes, while at the same time offering fairly sophisticated histogram and tone curve controls for those comfortable with more complex adjustments, and who need the control they provide.
As we write this, we're still searching for our "formula" that works best for scanner reviews, but are generally settling on a format in which we step through the scanner controls in the approximate order that a user would encounter them. (For a more complete walk-through of scanner operation, check out Minolta's excellent web site for their scanners: They've put together a comprehensive "on-line demo" of how the software works.)
The Control Window(s)
The most basic options and functions of the Dimage Scan Dual scanner are controlled via the Control window, shown below in its two versions. This window represents a merging of two windows on the earlier version of Minolta's scanning software, and greatly improves ease of use in our opinion. We liked many aspects of Minolta's scanning software in the past, but did find the concept of "Jobs" in the scanning setup rather confusing. For whatever reason, most scanner software seems to overly complicate the relationship between input and output resolution and file size. The two versions of the "Control" window take different approaches to handling this relationship, but both are simpler than most we've encountered, and are a significant improvement over earlier versions of Minolta's software.
Standard Control Window
The Dimage Scan software provides simplified scan-size options when operating in "Standard" mode. (See the Preferences screen described below.) In this mode, for the most part, you don't need to worry about pixels per inch, dots per inch, etc. You just tell the program what sort of output you're interested in (Screen, Pasted into a word processing document, or Printed or modified with PhotoDeluxe), and how much of the page you intend for the image to occupy, and the software figures out the pixels, magnification, etc. for you. Here are the controls available on the Standard Control Window. Note that the controls labeled "APS Only" do not appear in this window if 35mm is selected as the film type: (NOTE: This and all screen shots following have been scaled-down to better fit the 'web page -- The actual screens are larger and more readable!)
- Film Format (List Box) - Options are 35mm or APS, Color or B/W, Negative or Positive. For APS users, there's also an "auto detect" option for film type.
- Output (radio-button selection) - Choose the output type for your scan. This affects the options displayed below for Image size, whether expressed in pixels (Screen), paper size (Paste), or Paper Size (Print, as shown here).
- Image/Paper Size (pulldown menu) - (Could read "Image Size" if the "Screen" option was selected above.) Choose the basic dimensions of your
- Orientation (radio buttons) - Select Portrait or Landscape orientations, to have the final image appear in the file right-side up.
- Image (radio buttons) - Only active in the "Paste" or "Print" modes mentioned above. Sets the rough size of the scan to the indicated dimensions, relative to the Paper Size chosen above.
- Reset - Resets the scanning parameters back to the default values from the Preferences screen (see below).
- Preferences Button - Brings up the Preferences window, described later.
- Index Button (APS Only) - Brings up the Preferences window, described later.
- Save Index Scan Button (APS Only) - Brings up the Preferences window, described later.
- Prescan Button - Brings up the Preferences window, described later.
- Scan Button - Brings up the Preferences window, described later.
- Batch Scan Button - Brings up the Preferences window, described later.
- Help - (If you need us to explain what this button does, you probably shouldn't buy the scanner! ;-)
- Rewind Button (APS Only) - Rewinds APS film back into its canister.
- Exit Button - Exit the scanning control software and return to the host application (PhotoDeluxe)
Precision Control Window
This version of the control window provides much greater control over input size, output size, and resolution. Here, you can specify any element of the scanning resolution or image size, and the other parameters will follow in lockstep where appropriate. In the screen shot below, we've specified that we want to work in pixels, rather than inches or other linear measurements, so the Output resolution and Input Size windows are disabled. If you select inches, cm, or other measure in the "Unit" window, you'll have full control over all entry boxes. Many of the controls in this window are the same as in the Standard Control Window, so we won't repeat their descriptions here.
- Film Format (List Box) - Options are 35mm or APS, Color or B/W, Negative or Positive. For APS users, there's also an "auto detect" option for film type.
- Input (popup menu or direct numeric entry) - Select the input DPI for your scan. If you change the Output Size entries, this will scale accordingly
- Output (popup menu or direct numeric entry) - Select the output DPI for your scan. (Only if you're working in units other than pixels.) If you change the Input Size entries, this will scale accordingly
- Input Size (direct numeric entry or readout) - Enabled only when working in units other than pixels, otherwise just follows Output Size (see below). Set the input size of your image in whatever units you happen to be working in. (In most cases, you'll probably work by specifying output size and output DPI, rather than manipulating this
- Magnification (direct numeric entry or readout) - Shows the current ratio between input and output size.
- Output Size (direct numeric entry or readout) - Always active, even if "pixel" units are chosen. Select the output size in pixels, or in whatever units of linear measure you've chosen. See the discussion below for a more in-depth explanation of the interaction of the various data-entry fields...
- Unit - Choose the units you want to work in: Pixels (shown), mm, cm, inches, picas, or points.
- Save/Load Settings Buttons - To save time on subsequent scans (as well as provide a useful index of images on your APS rolls), you can save APS index scans to disk.
Preferences Dialog Box
The preferences window (not shown) controls a number of overall settings governing scanner operation. You'll probably need to visit this screen only infrequently, to set up the defaults for how you want the software to work. (For instance, whether to use the Standard or Precision Control Windows). Herewith the Preferences functions:
- Scanner Control - Options are "Standard" or "Precision", selecting which of the Control Windows described above is presented by default.
- Default Values
- Input Resolution - Set the default DPI (dots per inch) for your input resolution (scanning dpi on the film).
- Output Resolution - Set the default DPI for the resolution of output files.
- Unit - Set the default units of measurement (Pixels, mm, cm, inches, picas, or points)
- Auto Expose for Positive Film (slides) - On the Dimage Scan Speed, we found relatively little effect from this control, but on the Dimage Scan Dual, leaving it turned off tended to produce rather dark images when scanning slides. With the option enabled, default-setting slide scans were much closer to the "exposures" we ultimately wanted.
- Close Driver After Scanning - This will be most useful when using either a TWAIN or Photoshop acquire module for scanning. It will close the scanning window after each scan, returning you to the host application. (Or to the desktop, if you're running standalone.) If you're scanning multiple images at once though, you'll probably want to leave this box unchecked.
- Background Color You can choose a different background color for the preview scans. The default is a light gray, but if you're scanning images that will ultimately appear against a differently-colored background (such as black or white), you may want to change the background color in the scanning application to match.
- Film Settings:
- 35mm settings/Preview Size - Choose the size of preview images, as large, small, or auto. The auto setting will pick the largest setting that fits comfortably on your computer's display screen.
- 35mm settings/Scratch disk name - Choose the disk drive on your computer to be used to store temporary dtaa as high-resolution images are scanned.
- APS settings/Maximum frame - Set the maximum number of film frames that can be scanned in "batch" mode with the APS adapter. (We don't know why you'd want to limit this, other than to guard against running out of disk space.)
- APS settings/Rotate all frame - Some APS cameras feed the film from the left side, rather than the right, turning all the pictures upside down. This settings compensates for this, automatically rotating all images 180 degrees before displaying them on-screen.
- APS settings/Auto film rewind - Automatically rewinds film when "Exit" is selected.
This window (shown below) is "home base" for the scanning process. From here, you'll launch off into other functions within the software, to adjust color balance, contrast, or tonal range. Controls here also adjust preview orientation, data readout, and exposure parameters for sequential scans. See the text following the screen shot for a description of the individual buttons and controls.
Here are the Prescan Window controls, reading from left to right and top to bottom, for all the buttons along the bottom edge of the screen:
Orientation and Viewing Controls
(Grouped in the lower left-hand corner)
- Rotate Right Button - Rotates preview (and final scan) 90 degrees to the right. (Clockwise)
- Rotate Left Button - Rotates preview (and final scan) 90 degrees to the left. (Counterclockwise)
- Flip Horizontal Button - Flips picture horizontally.
- Flip Vertical Button - Flips picture vertically. (The two "flip" buttons find frequent use when flipping the slide or film carrier to scan frames at both ends.)
- Zoom In Button - Zooms in on a selected area of the pre-scan window.
- Zoom Out Button - Zooms in on a selected area of the pre-scan window.
- "Grabber" Button - This button turns the cursor into a "grabber", that lets you drag the pre-scan image and drag it around, to see various areas when the pre-scan image has been enlarged with the Zoom Button.
- APS Format Button (APS Only) - Lets you select between the 3 standard cropping dimensions for APS film, Conventional, HDTV, or Panorama, as well as fully-manual cropping as in 35mm mode.
Image Adjustment Controls
(Grouped in the lower right-hand corner. Most take you to secondary screens shown below, where you can modify the tone and color balance of the scanned image.)
- Variations Button - This leads to a screen (described in more detail below), where you can quickly adjust brightness and contrast, by the simple process of repeatedly choosing the most appealing of 8 alternate versions of the image. - An excellent tool for novices to quickly adjust their images.
- Tone Curves Button - Probably at the opposite end of the ease/power spectrum from the "variations" control, the tone curves screen (described in more detail later) provides the powerful ability to edit the tone curves for both the image as a whole, as well as the individual red, green, and blue channels.
- Histogram Button - This is our favorite scanning/image adjustment tool! (Also described in more detail later.) To our mind, histogram-based image adjustment offers the best tradeoff between ease of use and power for most mid-level users.
- Full-Screen View Button - Enlarges the currently-selected region of the pre-scan window to full-screen size. (Note though, that this enlargement is only a pixel replication, so it becomes rather pixellated when smaller regions are magnified.)
- Reset All Button - This button resets all the image adjustments to their default settings, letting you quickly back out of a set of adjustments and return to "zero."
At the bottom left-hand corner of the Prescan window, there are two sets of readouts, one showing the dimensions of the current cropping frame, in mm, and the other the RGB (or CMY) values of the point under the cursor in the preview window.
It's often difficult for novices to decide what to do to an image to make it look better. More contrast? Less brightness? A little of both? Frequently, after playing with an image for a few minutes, you end up with something that looks worse than when you started! Yet, even the rankest amateur can generally tell whether picture "A" looks better than picture "B". Taking advantage of this, Minolta offers a "Variations" tool, as shown in the screen shot below. Here, the current contents of your cropping frame are displayed in the center of a matrix of images, with those around the edges of it representing the effects of more or less contrast or brightness. (Contrast variations run vertically, brightness variations horizontally.) If you decide you like one of the variations presented more than the current image, just click on it: It becomes the new reference sample, and the variations adjust to reflect changes relative to the new center image. By continuing to click on the image that you like best, you can quickly home in on the optimum brightness/contrast setting.
After you've set the contrast and brightness, you can then correct the overall
color balance of the image, by adjusting the R, G, and B slider controls at
upper left. Always wait to adjust the color until after you've made the brightness
& contrast changes though, as you'll frequently find that perceived color
problems diminish once the brightness and contrast are properly set.
The "Variations" screen also has a button that enlarges the current selection to full-screen size, making it easier to assess the current picture quality. We felt that this feature was marred slightly though, by the fact that the enlarged image is only a pixel-replicated copy of the original area, which can lead to rather pixelated images if your cropping frame is small relative to the overall film area.
As we noted earlier, Histogram adjustments are by far our preferred method for quickly correcting tone and color problems in digital images! For those not familiar with histograms though, a brief explanation would probably be in order.
A histogram is simply a graph of how many pixels in an image have each possible brightness value. A large peak on a histogram graph means there's a lot of pixels (a large area) with roughly the same brightness values. Likewise, if the histogram curve is near zero, it means relatively few pixels have those brightness values. To understand how this helps image adjustment, we've included a couple of sample images below, showing two images set up with different brightness and contrast settings, and the histograms associated with each.
Dull, flat image has a compressed histogram, with no information above the midtone level in any channel.
In the first sample, we have a rather low-contrast, dark image. Low contrast means that there's not a great deal of difference in the brightness values between the brightest and darkest pixels. "Dark" means that the bulk of the pixels in the image have fairly low brightness values. In the histogram curves for this image, note how the right-hand side of the curves (high brightness values) are flat, because there aren't any pixels with those brightness values. Also, note how the histogram curves occupy a fairly small amount of the horizontal space allotted to them.
Well-balanced image shows full range of tonal values in histogram, in all channels.
By contrast (no pun intended!), observe the image above: Contrast and brightness are about right, and the results are readily evident in the histogram curves for it. Notice how the curves occupy much more of the available horizontal space, meaning that pixel values are spread much more evenly across the available tonal range. Notice too, how you can even tell about color balance from histogram displays. Notice the large "hump" near the middle of each curve? What object in the image do you suppose this large group of pixel values corresponds to? (It's the background.) Now, if we want the background to be a neutral gray, what do you suppose the display would look like. (The peaks in red, green, and blue would all line up with each other, meaning that the average R, G, and B values would be about the same.) Can you guess how the color balance needs to be adjusted to achieve this?
Notice the sliders under the individual histogram curves. These are used to set the brightness values the scanner will consider to be the minimum (black), maximum (white), and a middle value (gray), for each of the color channels. If you move the "black" slider up from the leftmost position, you're telling the scanner to treat that value as "zero" for the color channel involved. Any values darker than that will also be treated as zero, and values brighter than it will be proportionately stretched downward so that the brightness values will extend smoothly down to zero. Likewise, the "white" slider on the right sets the value that will be considered as a maximum, and mapped to a digital value of 255. Anything brighter will also be set to 255, and darker values will be "stretched" smoothly. The middle slider sets the value that the scanner will put in the middle of the brightness scale (the "50%" point). Anything brighter than the level set by the slider will be made brighter than 50%, anything darker will be made darker. Thus, to lighten the image overall, you'd move this slider to the left, so that more of the brightness values would be pushed above the 50% point. (This all sounds more complicated than it is: You'll figure out what the sliders do after just a couple of minutes of playing around.)
The histogram screen includes "before" and "after" previews, and a number of controls for adjusting the image. At middle left are three of the most immediately useful tools, the eyedroppers for setting white, black, and gray points. If you select the black eyedropper button, and then click on a point in the left-hand preview window, that point will be set as the "black" point, and the individual red, green, and blue black-point sliders will all adjust automatically to make it so. Likewise, selecting the white eyedropper button and clicking in the left-hand preview window will set that point as the "white" point, moving the red, green, and blue white-point sliders as needed. (Anyone want to guess what the gray eyedropper button does?) In practice, you'll find that the eyedropper controls offer a very quick way to color-balance many problem images in a matter of seconds.
Part of the beauty of the Dimage Scan's histogram screen is the way it shows
histograms for all three color channels separately, yet also allows you to operate
on all the channels at the same time, if you wish. By default, you can adjust
any of the slider controls independently of any other. What if you want to make
an overall adjustment to the image as a whole, though? In the lower left-hand
corner, the button with the three colored bands on it is the "RGB synchro
button." Clicking this button locks the sliders for the red, green, and
blue histograms together, so that moving any one of them moves the sliders for
the other two colors the same amount.
The other control buttons in the lower left-hand corner let you see the effects of your adjustments on the histogram, as well as save and retrieve complete sets of adjustments once created. This last ability is a particularly welcome one, as many lower-end scanners don't permit you to save adjustments for later use. Often, we find ourselves wanting to save a group of settings before engaging in further experimentation, so we have a known good point to return to if our twiddling goes awry. Also, you may have a group of photos shot under similar conditions that would all benefit from the same treatment.
One odd point about saved and subsequently recalled histogram corrections though: When the Dimage Scan software applies a previously saved correction to an image, it does so on top of whatever correction may currently be in effect. Thus, the effects of recalled corrections are cumulative with any you've already applied. If you want to return to a prior state, you'll need to reset all corrections (using the Reset button) before applying the saved settings. (This isn't any sort of a problem, but was different than how we expected the saved settings to work. We're passing the information along here to hopefully save our readers a few minutes of puzzlement when they encounter the behavior for the first time.)
A full treatment of histogram-based tonal adjustments is far beyond the scope of this review, but we encourage users to spend some time playing with the controls on this screen: They're simple to master, but quite powerful to use.
Tone Curve Adjustments
The tone curves window (shown below) offers a set of controls that are at once easier to understand than those of the histogram display, yet considerably less straightforward to apply effectively. Even here though, minor tweaks by Minolta contribute greatly to ease-of-use.
In concept, tone curve controls are as simple as can be: They're nothing more than a graph of output brightness values against input brightness values. Essentially, they say "whenever you see brightness 'x', replace it with brightness 'y'. The input brightness values (those of your original image) are arranged along the horizontal axis of the graph, and the output values (those your image will come to assume) are arranged along the vertical axis. Again, the easiest way to understand how a tone curve works is to play with one. A little experimenting will reveal that a steeply sloping curve produces high contrast, while a flatter one produces less. Likewise, a curve bulging upward results in a brighter image overall, and one drooping downward makes for a darker one. The Dimage Scan software lets you adjust either the overall RGB curve, or each of the color channels (red, green, and blue) individually.
Tone curve controls let you adjust parts of the tonal scale, without affecting
others. As such, they're more powerful than the histogram controls, but you
have less feedback as to what parts of the image you're affecting, and it's
much easier to get lost in your adjustments with them. Experienced graphics
professionals rely on tone-curve adjustments almost exclusively though, because
they provide such a high degree of control over the tone and color balance of
The tone curve controls in the Dimage Scan software work like those of most any high-end image editing program: You can click any point on the curve and drag it, and the rest of the curve will bend smoothly to pass through the point you've defined. You can set multiple control points by clicking on more than one part of the curve. You also have the ability to draw your own curve, using a pencil tool, allowing you to create abrupt discontinuities if desired. Minolta added a unique twist to the tone curves though, in the form of white and black-point eyedropper controls, which work in the same way as the equivalent controls on the histogram screen. While a seemingly minor point, the eyedroppers can quickly make gross adjustments in the overall tone and color balance, and provide a good jumping-off point for your own finer adjustments.
As always with Imaging Resource reviews, we encourage you to let your own eyes be the final judge: Look at the sample images, download them, print them out on your own printer, and decide for yourself how well the Dimage Scan Dual would meet your requirements!
Overall, the Dimage Scan Dual turned in a good performance, competing well in the "personal" scanner catetory with other units in its price range. Particularly when compared to the digital cameras that constitute the other major review focus of this site, readers are bound to be impressed with the incredible amounts of detail a scanner like the Dimage Scan Dual can extract from a slide or negative.
We found that the Dimage Scan Dual produced good scans with the default settings, and that the software controls available made for easy modification of the images. On the Mac, the default settings tended to produce slide scans that were slightly dark with our screen gamma set to the "standard" value of 1.8 - Actually, the scans were a little light when no explicit gamma settting was made. A minor bump of the midtone point using the histogram control quickly brought the overall tone into a reasonable range though.
By comparison, scans of color negatives were a bit light, but a minor drop of the midtone point tended to quickly compensate. Color balance overall was quite good, although by default, the scanner tended to add a bit of magenta to things (red and blue together). We suspect this might be an attempt to compensate for typical computer monitors, which tend to have a very bluish white-point, frequently as high as 9300K. Again, it wasn't too difficult to compensate for this tendency, and the ability to save and recall sets of tone and color corrections was a valuable feature. Overall color accuracy was excellent, with color saturation just a notch away from the very best we've seen to date (January, 1999). (Like the Dimage Scan Speed though, color saturation in greens on transparency (slide) scans is a bit weak.)
Resolution of the Dimage Scan Dual was excellent, but hard to "call" based on our standard test targets. The reason for this is that an unusually low level of "aliasing" had us convinced we could easily see discernible detail in the WG-18 target all the way out to 1400 lines per picture height in both horizontal and vertical directions. This doesn't make sense, given that there are only 2600 pixels vertically in the resolution-target image, meaning we really "shouldn't" be able to see anything beyond about 1150 line pairs/picture height. Nonetheless, the scanner clearly resolves at least some detail all the way out to 1400 l/ph. (Note that the slight cropping the scanner did to the 35mm frame wouldn't be nearly enough to produce the increase in apparent resolution we observed.)
The USAF resolution target gave (as usual) more conservative resolution figures, with the scanner resolving cleanly down to 28.5 line pairs/mm, (724 line pairs/inch), and with some aliasing, down to 45.3 lp/mm (1151 line pairs/inch). With natural subjects, the scanner's fluorescent light source produced a somewhat softer, less grainy look than some other units we've tested, although there seemed to be no loss of detail information in the scans associated with this softer "look".
See for Yourself!
Take a look at the test images from the Dimage Scan Dual, download them, print them out, and see if this scanner meets your needs!
In the Dimage Scan Dual, Minolta has crafted a combination of capabilities and software features into a unit that produces good image quality with a minimum of tweaking. Even better, when it does come time to manipulate color and tone, the software controls provide a full range of capabilities, satisfying users ranging from rank amateur to experienced.
View the Test Images from the Dimage Scan Dual
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