Canon Powershot S70

S70 Sample Images

Excellent resolution and detail, with low image noise. Good overall color, though high contrast.

The extreme tonal range of this image makes it a tough shot for many digicams, which is precisely why I set it up this way, and why I shoot it with no fill flash or reflector to open the shadows. The object is to hold both highlight and shadow detail without producing a "flat" picture with muddy colors, and the PowerShot S70 produced good color, but slightly high contrast, even with its low contrast option selected.

The shot at right was taken with a +0.7 EV exposure compensation adjustment, about average for this shot. With the help of the camera's low-contrast option, it held onto the highlight detail pretty well, but at the cost of somewhat dark midtones and shadows. (This photo will probably look a bit underexposed to most people's eyes, but I wasn't willing to give up as much highlight detail as was lost in the version shot at +1.0 EV.) Despite a very slight red cast, I chose the Auto white balance setting, though results with the Daylight are also good. (The Manual option resulted in a stronger red cast.)

Marti's skin tones are just slightly reddish here, but still in the range of what I'd characterize as "very good." The blue flowers in the bouquet are a little darker and more purplish than in real life, but overall pretty close to the correct color. The red flowers are slightly oversaturated, but aren't too far out of range, and saturation looks pretty good in the strong greens and yellows. Resolution is outstanding, as the S70's 7.1-megapixel CCD captures excellent detail throughout the frame, even in Marti's facial features. (And the S70's anti-noise processing seems to leave a good amount of detail in the subtly-shaded areas of Marti's hair, a good trick these days.) Detail is very good in the shadow areas as well, despite the high contrast, and image noise in the shadows is lower than I'm accustomed to seeing.

To view the entire exposure series from -0.3 to +1.0 EV, see files S70OUTBAM1.HTM through S70OUTBAP3.HTM on the thumbnail index page.

Contrast Series:
The S70's contrast adjustment works very well. As was the case with the G6 (basically the same camera, just in a different case and with a hot shoe for flash use), the low contrast option seems to affect the highlights more than the shadows, while the contrast boost appears to affect highlight and shadow areas more or less equally. The contrast adjustment also has relatively little effect on color saturation, something that's not always the case. I'd like to see a bit wider range of adjustment, particularly in the low-contrast direction, as well as more/finer steps, but the control as it exists is more effective than that on most digicams I test.

Contrast Series
Low	Normal	High

Saturation Series:
Likewise, the saturation adjustment on the S70 does very well also, although I'd perhaps like to see five steps covering the same range, and a little less impact on image contrast.

Saturation Series
Low	Normal	High

Outstanding resolution with incredible fine detail. High contrast though.

Exposure and color are similar to the wider shot above, though this shot required only a +0.3 EV exposure compensation adjustment. Contrast is again high, with slightly harsh highlights and dark midtones. The S70's 3.6x zoom lens helps prevent geometric distortion of Marti's features, and captures sharp details very well. Resolution and detail are even stronger in this close-up shot, with excellent definition in Marti's face and hair. Even the minute details of the leaf fabric and gold chain around her neck are very clear and distinct.

This shot shows more of the loss of detail in regions of subtle contrast that's characteristic of anti-noise processing: Check out the middle tones of Marti's hair, just on the right side of her forehead. You can see how the individual strands of hair become indistinct when the contrast between them drops below a certain value. Still, I'd rate the S70 as being better than average in this respect, this is an impressive job, on all fronts.

To view the entire exposure series from -0.3 to +1.0 EV, see files S70FACBAM1.HTM through S70FACBAP3.HTM on the thumbnail index page.

Normal Flash +0.7 EV

Slow-Sync Flash +0.7 EV

Good coverage with the built-in flash, though a slight underexposure at the default exposure. Good overall color as well, and nice results with the Slow-Sync setting.

The S70's built-in flash underexposed slightly at the default exposure, though coverage was pretty good. I chose an exposure compensation boost of +0.7 EV for the main shot. Overall color is very good, with only a slight red tint and a small orange cast on Marti's hair from the strong incandescent room lighting. (Interestingly, the S70 did quite a bit better on this shot than the G6 did, the version shot in normal flash mode showing much less color cast from the background lighting.) I also shot with the camera's Slow-Sync flash mode, again choosing a +0.7 EV exposure compensation adjustment. Lighting is more even in this shot, as the longer exposure allows more of the ambient light in to balance the image. However, the longer exposure also increases the warm cast, but overall color still isn't bad.

To view the entire exposure series in the normal flash mode from -0.3 to +1.0 EV, see files S70INFM1.HTM through S70INFP3.HTM on the thumbnail index page.

To view the same exposure series in the Slow-Sync flash mode, see files S70INFSM1.HTM through S70INFSP3.HTM on the thumbnail index page.

Auto White Balance

Incandescent White Balance

Manual White Balance

Trouble with automatic white balance, but good results with both Incandescent and Manual settings, good exposure as well.

This shot is always a very tough test of a camera's white balance capability, given the strong, yellowish color cast of the household incandescent bulbs used for the lighting. The S70's Manual and Incandescent white balance settings both produced nearly accurate results here. It was a bit of a tossup which looked the best, I settled on the Incandescent version as the main selection for this shot. The camera's Auto setting quite a bit of trouble producing a very warm color cast. I obtained the best exposure with a +1.0 EV exposure compensation adjustment, in most of the shots, although oddly, the Incandescent white balance seemed to require a little less compensation that the other modes. (The Incandescent shot at right was captured with +0.7 EV of adjustment.) The blue flowers in the bouquet are a little dark and purplish, but actually look pretty good considering the difficult light source. There's also a modest amount of image noise in these ISO 100 shots (the standard ISO that I shoot this subject at), but isn't very visible unless you look specifically at the image's blue channel. - There is more evident flattening of subtle subject detail visible in this shot though.

ISO Series:
Image noise is present here at ISO 50, but it's at a pretty low level, increasing gradually as the ISO is increased. At ISO 200, it would almost certainly be visible to most observers, and there's a fair loss of subtle detail caused by the anti-noise processing as well. At ISO 400, image quality is pretty marginal, IMHO. (Interestingly, image noise in the S70 seems somewhat higher than in the G6. Even allowing for the slightly lower exposure in the S70's versions of this test, it's my feeling that the G6's image noise is clearly lower overall.)

Auto White Balance

Daylight White Balance

Manual White Balance

Excellent resolution and detail, with great color.

The S70's Manual white balance produced the best overall color here, with the most accurate white value on the house trim. That said, the Auto and Daylight settings also produced good results, though with slightly warmer casts. Resolution is very high, and detail is very strong in the fine foliage in front of the house, as well as in the tree limbs above the roof. House details such as the brick pattern and trim are also quite clear. (I should point out though, that the S70's seven-megapixel CCD stretches the limits of this poster as a test target. Even though the poster was made from a 500MB scan of a 4x5 negative shot with a tack-sharp lens, the S70 is close to extracting all the detail that's to be found here.) Details are sharp throughout most of the frame, though the bottom corners appear softer.

(For what it's worth, the performance of the S70 and G6 are very close on this image, despite their very different lenses. I think the G6 has a slight but noticeable edge in terms of overall sharpness and detail, but the difference is so slight as to be academic.)

Excellent resolution and detail, though high contrast limits the camera's dynamic range.

This image is shot at infinity to test far-field lens performance. NOTE that this image cannot be directly compared to the other "house" shot, which is a poster, shot in the studio. The rendering of detail in the poster will be very different than in this shot, and color values (and even the presence or absence of leaves on the trees!) will vary in this subject as the seasons progress. In general though, you can evaluate detail in the bricks, shingles and window detail, and in the tree branches against the sky. Compression artifacts are most likely to show in the trim along the edge of the roof, in the bricks, or in the relatively "flat" areas in the windows.

This is my ultimate "resolution shot," given the infinite range of detail in a natural scene like this, and the S70 does an excellent job in that respect. Details are amazingly crisp and clear in the fine leaf patterns of the front shrubbery, as well as in the tree limbs and leaves over the roof. Details are sharp and crisp just about everywhere, although there is some very noticeable softness along the right edge of the frame, and particularly in the upper and lower right hand corners. Dynamic range is a little limited though, as the loses essentially all detail in the bright white paint surrounding the bay window, a trouble spot for many digicams. Detail is a little limited in the shadows around the door, but not too bad, relative to the results produced by many cameras. The table below shows a standard resolution and quality series, followed by ISO, sharpness, contrast, saturation, and effects series.

Resolution Series:

ISO Series:
As before, noise levels here are pretty good for a 7 megapixel camera, but it looks like the G6 once again just slightly edges out the S70 in the noise department.

Sharpness Series:
The S70's default image sharpening manages to achieve a good balance, producing good sharpness with relatively few defects. For the ultimate in image detail and resolution though, use the low sharpening option and sharpen on the computer with Photoshop(tm) or other imaging software. - Image shot with the in-camera sharpening set to "low" take unsharp masking unusually well. (Try 250% at 0.3 pixel radius to see some amazing detail.)

Contrast Series:

Contrast Series
Low	Normal	High

Saturation Series:

Saturation Series
Low	Normal	High

Effects Series:

Effects Series
Low Sharpening	Vivid Color	Neutral Color	Black and White	Sepia

Lens Zoom Range

A good 3.6x zoom range.

I routinely shoot this series of images to show the field of view for each camera, with the lens at full wide angle, at maximum telephoto (3.6x, in this case), and at full telephoto with the digital zoom enabled. The S70's lens is equivalent to a 28-100mm zoom on a 35mm camera. That corresponds to a fairly wide angle to a moderate telephoto. (On a down note though, I do see more chromatic aberration and softness in the corners at the 28mm focal length than I'd ideally like.) Following are the results at each zoom setting.

Auto White Balance

Daylight White Balance

Manual White Balance

Good color, excellent detail.

This shot is often a tough test for digicams, as the abundance of blue in the composition frequently tricks white balance systems into producing a warm color balance, but the S70 did very well with it. I preferred the S70's Auto white balance setting on this shot, as the Manual setting was a hint cool and the Daylight setting a little too warm. Overall color looks pretty good, though the blue robe has slight purplish tints, as does the blue background. Resolution is excellent, as detail is very strong in the models' features and clothing, especially in the beaded necklaces, embroidery on the blue robe, and flower garland. (The original data file for this poster was only 20MB though, so cameras like the S70 are definitely capable of showing more detail than the poster has in it.)

Standard Macro Shot

Macro Shot with Flash

A very small macro area with excellent detail, but the flash has trouble up close.

The S70 captured a tiny macro area, measuring only 2.26 x 1.69 inches (57 x 43 millimeters). Resolution is very high, and detail is very strong in the dollar bill. Details are softer in the coins and brooch, partly due to the close range and partly to some distortion from the lens that softens detail in the corners of the frame. (Shallow depth of field is an optical fact of life in macro shooting, so isn't the camera's fault. Softness in the corners of images is a consequence of curvature of field in the camera's optics, and is unfortunately a near-universal limitation with digicam macro options.) The S70's flash had trouble throttling down for the macro area, and overexposed the shot. (The camera's lens also blocks part of the flash in the lower right corner.) - Plan on using external lighting for your closest macros shots with the S70.

Auto White Balance

Daylight White Balance

Manual White Balance

Good overall exposure, though a warm color cast.

The S70's Auto white balance setting produced good results here, as did the Manual setting (though with just a hint of a red cast). The Daylight setting resulted in a warmer cast. Exposure is good, though maybe a little bright, and the S70 distinguishes the subtle tonal variations of the Q60 target well. The large color blocks are generally hue-accurate, and show slightly higher color saturation than did the G6 on this target, perhaps as Canon has aimed the S70 a little more at the consumer market, rather than the "enthusiast" one. Detail is strong in the shadow area of the charcoal briquettes, with low noise, and the camera easily distinguishes between the two darkest steps of the large Kodak gray scale. An excellent performance.

Now, for the REAL technoids, Imatest!

I've recently begun using Norman Koren's excellent "Imatest" analysis program for quantitative, thoroughly objective analysis of digicam test images. For those interested, I've prepared a page summarizing what Imatest showed me about the PowerShot S70's images.


The results in the tests below mirror those seen above in other test shots. The test series are repeated here without further comment, for the benefit of our more quantitatively-oriented readers.

ISO Series:

Contrast Series:

Contrast Series
Low	Normal	High

Saturation Series:

Saturation Series
Low	Normal	High

Effects Series:

Effects Series
Low Sharpening	Vivid Color	Neutral Color	Black and White	Sepia

Low-Light Tests

Very good low-light performance, with bright images and good color to the limits of my test. Good focusing with the AF illuminator as well.

The S70 produced clear, bright, usable images with good color down to the 1/16 foot-candle (0.67 lux) limit of my test at ISOs 200 and 400, though images were bright to only 1/4 foot-candle (2.7 lux) at ISO 50 and to about 1/8 foot-candle (1.3 lux) at ISO 100. (Average city street lighting at night corresponds to a light level of about 1 foot-candle.) Color balance was pretty good, though pinkish at the lower exposures. Noise was low, at the 50 and 100 ISO settings, creeping upward at ISO 200, and becoming high at ISO 400. Interestingly, while the noise of the S70 is numerically lower than that of the G6, I personally find it a little more annoying. It isn't quite as fine-grained, and the S70 also seems to lose a little more subtle subject detail to its anti-noise processing than the G6 does. The net result is still very good, the S70 did very well in this low-light test. - It's just that it's not quite as good as the G6 here. The table below shows the best exposure I was able to obtain for each of a range of illumination levels. Images in this table (like all sample photos) are untouched, exactly as they came from the camera.

(Note: If you'd like to use a light meter to check light levels for subjects you might be interested in shooting, a light level of one foot-candle corresponds to a normal exposure of two seconds at f/2.8 and ISO 100.)

	1 fc 11 lux	1/2 fc 5.5 lux	1/4 fc 2.7 lux	1/8 fc 1.3 lux	1/16 fc 0.67 lux
ISO 50	3.2 sec f2.8	6 sec f2.8	13 sec f2.8	15 sec f2.8	15 sec f2.8
ISO 100	1.6 sec f2.8	3.2 sec f2.8	6 sec f2.8	13 sec f2.8	15 sec f2.8
ISO 200	1/1 sec f2.8	1.6 sec f2.8	3.2 sec f2.8	6 sec f2.8	13 sec f2.8
ISO 400	1/2 sec f2.8	1/1 sec f2.8	1.6 sec f2.8	3.2 sec f2.8	6 sec f2.8

Flash Range Test

A bright flash, but with noticeable falloff beyond 10 feet.

In my testing, the S70's flash was pretty bright, with an apparent range of about 10 feet. (Exposure was pretty uniform until about 10 feet, and decreased progressively beyond that point.) Below is the flash range series, with distances from eight to 14 feet from the target.

8 ft	9 ft	10 ft	11 ft	12 ft	13 ft	14 ft
1/60 sec f5.3	1/60 sec f5.3	1/60 sec f5.3	1/60 sec f5.3	1/60 sec f5.3	1/60 sec f5.3	1/60 sec f5.3

ISO-12233 (WG-18) Resolution Test

Very high resolution, 1,500-1,550 lines of "strong detail." High barrel distortion, but no pincushion.

The S70 performed almost identically to the G6 on the "laboratory" resolution test chart. It didn't start showing artifacts in the test patterns until resolutions around 1,200 lines per picture height vertically, but around 1,000 lines horizontally. I found "strong detail" out to at least 1,550 lines horizontally, but only to about 1,500 lines vertically. (And there were strong aliasing artifacts a good 100-150 lines lower than these levels.) "Extinction" of the target patterns didn't occur until about 1,900 lines.

Using its "MTF 50" criteria, Imatest reported uncorrected resolution figures of 1305 line widths per picture height in the horizontal direction (corresponding to the vertically-oriented edge), and 1283 along the vertical axis (corresponding to the horizontally-oriented edge), for a combined average of 1294 LW/PH. Correcting to a "standardized" sharpening with a one-pixel radius increased both the horizontal and vertical numbers quite a bit, giving a corrected average of 1573 LW/PH, an excellent result.

Optical distortion on the S70 was higher than average at the wide-angle end, where I measured approximately 1.05 percent barrel distortion. The telephoto end fared much better, as I couldn't find so much as a full pixel of pincushion or barrel distortion. Chromatic aberration is low at medium and telephoto focal lengths, but becomes quite high at the wide angle end, with as much as 8-9 pixels of fairly strong color visible around the target pattern in the corners. (This distortion is visible as a very slight colored fringe around the objects at the edges of the field of view on the resolution target.) Likewise, the lens also shows a fair bit of softness in the corners of the image, probably about an average amount for a wide-zoom camera, which is to say, a fair bit more than shown by the G6. The S70's lens isn't bad, but it's clear that this is one of the main areas in which the S70 suffers in comparison to the G6.

Resolution Series, ~50mm equivalent focal length

Wide Angle	"Fine" JPEG	"Normal" JPEG	"Economy" JPEG
3,072 x 2,304	S70RES3072F	S70RES3072N	S70RES3072E
2,592 x 1,944	S70RES2592	-	-
2,048 x 1,536	S70RES2048	-	-
1,600 x 1,200	S70RES1600	-	-
640 x 480	S70RES0640	-	-

 

Resolution Test, Zoom Series

3,072 x 2,304 (Fine, Wide Angle)	S70RESW
3,072 x 2,304 (Fine, Tele)	S70REST

Sharpness Series