Canon 7D Imatest Results

We routinely use Norman Koren's excellent "Imatest" analysis program for quantitative, thoroughly objective analysis of digicam test images. I highly recommend it to our technically-oriented readers, as it's far and away the best, most comprehensive analysis program I've found to date.

My comments below are just brief observations of what we see in the Imatest results. A full discussion of all the data Imatest produces is really beyond the scope of this review: Visit the Imatest web site for a full discussion of what the program measures, how it performs its computations, and how to interpret its output.

Here's some of the results produced by Imatest for the Canon 7D:


sRGB Accuracy Comparison

The Canon EOS 7D showed very good color accuracy, as well as fairly accurate saturation levels. Hue accuracy was quite good, with small hue shifts occurring mainly in the cyans, reds, oranges and some browns and purples. Average "delta-C" color error was only 4.81 after correction for saturation, which is very good. (Delta-C is the same as the more commonly referred to delta-E, but delta-C takes into account only color differences, ignoring luminance variation.) Average saturation was 106.8% (6.8% oversaturated), which is also very good. Mouse over the links below the illustration above to compare results with competing models.

 

Adobe RGB Accuracy Comparison

Like most other cameras, the Canon EOS 7D delivers more highly saturated colors when using the Adobe RGB color space (which provides a much wider gamut, or range of colors that can be expressed). Average saturation was 114.6%, which is higher than the sRGB results. Average saturation-corrected hue error was 6.08 "delta-C" units, less accurate than the sRGB result, but still pretty good. Again, mouse over the links below the illustration above to compare results with other semi-pro APS-C SLRs.

 

Canon EOS 7D Color Analysis

This image shows how the Canon EOS 7D actually rendered the colors of the MacBeth chart, compared to a numerically ideal treatment. In each color swatch, the outer perimeter shows the color as actually captured by the camera, the inner square shows the numerically correct color after correcting for the luminance of the photographed chart (as determined by a second-order curve fit to the values of the gray swatches), and the small rectangle inside the inner square shows the numerically correct color, without the luminance correction. This image shows the very good hue accuracy of the 7D, as well as a contrast curve that results in moderate overexposure of some of the highest-saturation swatches. (This increase in luminance for the highly-saturated swatches seems to be a fairly common tactic, to produce "bright" color that's appealing to consumers, without further overdoing the saturation.)

 

Canon EOS 7D Noise Analysis


There's a lot in this particular graph, a lot more than we have room to go into here. (This set of plots has also changed a few revisions back in Imatest. Some of the plots that were once shown here are now shown in other Imatest output. Since we largely focus on the Noise Spectrum plot, we only show the graphic above, which includes that plot.)

In comparing these graphs with those from competing cameras, we've found that the Noise Spectrum graph at lower right is the most important. Cameras that manage to shift their noise spectrum to higher frequencies have much finer-grained noise structures, making their noise less visually objectionable. In the graph above, this would show up as a noise spectrum curve that remained higher on the right side, representing higher noise frequencies.

Here, we can see the Canon 7D does a good job at keeping luminance noise (indicated by the black line) at higher frequencies, though the slope of the luminance plot isn't quite as flat as some other cameras in its category, including the Canon 50D and the Nikon D300S. The result is a fine noise "grain" that is slightly visible at ISO 100, when pixel peeping at deeper mid-tones and shadows. Still, this is very good performance, considering the 7D's higher than average pixel count. Like many cameras these days, the chrominance channels (especially red) have higher noise levels at lower frequencies, though the 7D's chroma noise at low ISOs much better controlled than its predecessor, the 50D.

 

Here's the same set of noise data at ISO 3,200. Here, the Noise Spectrum graph is shifted towards the left-hand, lower-frequency side than it was at ISO 100. This indicates a coarsening of the "grain" of the image noise patterns by quite a bit, and indeed that's what we see when inspecting the 7D's ISO 3,200 images. The chrominance channels' noise spectrum follows that of the luminance channel much more closely, a result of the default high ISO noise reduction applied, but is still a bit higher at very low frequencies. This can be seen in high ISO images as large but subtle blotches of chroma noise in darker areas, spread across multiple pixels. That said, the Canon 7D does a better than average job at keep chrominance noise in check.

 

Here's the same set of noise data at ISO 6,400. The Noise Spectrum graph has shifted slightly more to the left, and the 7D's default noise reduction has kept the chroma noise spectrum closely following luminance noise. Notice however that the total noise levels are much higher. (Particularly evident in the pixel noise plot in the upper right corner of the illustration, and in the midtones and below in the graph in the lower left hand corner.) When looking at the 7D's ISO 6,400 shots, there are quite a few bright noise pixels visible, especially in dark areas.

 

Here's the same set of noise data at ISO 12,800. The Noise Spectrum graph has shifted even further to the left. Notice again that the total noise levels are even higher, as expected. When examining the 7D's ISO 12,800 shots, many bright noise pixels are quite evident, especially in the shadows and darker areas, however there is a definite improvement over the 50D in this regard.

 

This chart compares the Canon EOS 7D's luminance noise performance at midtone grey density over a range of ISOs against that of other current, semi-pro SLR models. While we continue to show noise plots of this sort because readers ask for them, we each time point out that the noise magnitude is only a small part of the story, the grain pattern being much more important. Here, we can see that the Canon EOS 7D's luminance noise magnitude starts out slightly above average (if we ignore the much higher levels from the Pentax K-7), and remains average to slightly above average up to ISO 6,400. The only other camera in the group capable of ISO 12,800 is the Canon 50D, and the 7D's luminance noise magnitude is significantly lower at that ISO. As mentioned previously, when comparing the 7D's ISO 6,400 and 12,800 images to the 50D's, it's clear the 7D does a better job at reducing the number of (but not eliminating) hot or bright noise pixels that are common in the 50D's very high ISO images. It's also interesting to note that the 50D seems to do better at ISO 1,600 in this regard; having fewer bright noise pixels than the 7D, which is reflected in the plots above. (Keep in mind these are at default noise reduction settings, so the shape of the curve can be influenced by the noise-reduction settings you employ. The Canon EOS 7D offers 4 levels of high ISO noise-reduction to choose from, including "Off".)


 

Canon EOS 7D Dynamic Range Analysis

A key parameter in a digital camera is its Dynamic Range, the range of brightness that can be faithfully recorded. At the upper end of the tonal scale, dynamic range is dictated by the point at which the RGB data "saturates" at values of 255, 255, 255. At the lower end of the tonal scale, dynamic range is determined by the point at which there ceases to be any useful difference between adjacent tonal steps. Note the use of the qualifier "useful" in there: While it's tempting to evaluate dynamic range as the maximum number of tonal steps that can be discerned at all, that measure of dynamic range has very little relevance to real-world photography. What we care about as photographers is how much detail we can pull out of the shadows before image noise becomes too objectionable. This, of course, is a very subjective matter, and will vary with the application and even the subject matter in question. (Noise will be much more visible in subjects with large areas of flat tints and subtle shading than it would in subjects with strong, highly contrasting surface texture.)

What makes most sense then, is to specify useful dynamic range in terms of the point at which image noise reaches some agreed-upon threshold. To this end, Imatest computes a number of different dynamic range measurements, based on a variety of image noise thresholds. The noise thresholds are specified in terms of f-stops of equivalent luminance variation in the final image file, and dynamic range is computed for noise thresholds of 1.0 (low image quality), 0.5 (medium image quality), 0.25 (medium-high image quality) and 0.1 (high image quality). For most photographers and most applications, the noise thresholds of 0.5 and 0.25 f-stops are probably the most relevant to the production of acceptable-quality finished images, but many noise-sensitive shooters will insist on the 0.1 f-stop limit for their most critical work.

The graphic below shows the test results from Imatest for an in-camera JPEG file from the Canon EOS 7D with a nominally-exposed density step target (Stouffer 4110), and the 7D's contrast and other exposure-related settings such as Auto Lighting Optimizer at their default values.

Here, with Auto Lighting Optimizer set to Standard by default, we can see that the tone curve shows excellent gradation in the highlights, but the shadow end trails off abruptly. This can be seen when closely inspecting shots captured by the 7D, where detail is held very nicely in strong highlights, but somewhat less so in the deepest shadows. Total dynamic range reported is 10.3 f-stops while dynamic range at the highest quality level is 7.54 f-stops. This is about average for a modern SLR with an APS-C size sensor.

 

Here is the same plot with ALO set to Off. As you can see, very similar results, though the Standard ALO setting did produce slightly higher scores.

 

Processing the Canon EOS 7D's RAW (.CR2) files through Adobe Camera Raw (ACR) version 5.6 increased dynamic range by about 2/3 f-stops at the highest quality level (8.18 f-stops), compared to the in-camera JPEG (7.54 f-stops), while total dynamic range reported increased by about 1.2 f-stops from 10.3 to 11.5. These results were obtained by using ACR's automatic settings. It's possible to get slightly better results with manually tweaking, but we weren't able to. It's worth noting here that ACR's default noise reduction settings reduced overall noise (see the plot in the lower left-hand corner) relative to the levels in the in-camera JPEG, which would tend to boost the dynamic range numbers for the high quality threshold.


Dynamic Range, the bottom line:

The net result was that the Canon EOS 7D's JPEGs and ACR converted RAW files scored about average in Imatest's dynamic range analysis when compared against other current APS-C sensor models.

To get some perspective, here's a summary of the Canon EOS 7D's dynamic range performance, and how it compares to other digital SLRs that we also have Imatest dynamic range data for. (Results are arranged in order of decreasing dynamic range at the "High" quality level.):

Dynamic Range (in f-stops) vs Image Quality
(At camera's base ISO)

(Blue = RAW via ACR, Yellow=Camera JPEG, Green=Current Camera)
Model 1.0
(Low)
0.5
(Medium)
0.25
(Med-High)
0.1
(High)
Nikon D3X
(Adobe Camera Raw 5.3b)
-- -- 11.1 9.64
Nikon D700
(Adobe Camera Raw 4.5)
12.1 11.6 10.6 9.51
Nikon D5000
(Adobe Camera Raw 5.4b)
-- 11.6 10.8 9.50
Sony A900
(Adobe Camera Raw 4.6b)
-- 12.1 10.7 9.36
Pentax K-x
(Adobe Camera Raw 5.6b)
11.5 11.2 10.7 9.33
Nikon D90
(Adobe Camera Raw 4.6b)
12.1 11.8 10.7 9.27
Fujifilm S3 Pro
(Adobe Camera Raw 2)
12.1 11.7 10.7 9.00
Sony A230
(Adobe Camera Raw 5.5)
11.7 11.1 10.1 8.95
Nikon D40x
(Adobe Camera Raw 4.1)
12.0 10.9 10.3 8.90
Nikon D300S
(Adobe Camera Raw 5.5)
-- 11.3 10.4 8.89
Canon 5D Mark II
(Adobe Camera Raw 5.2)
-- 10.8 10.0 8.89
Sony A330
(Adobe Camera Raw 5.4)
-- -- 10.1 8.86
Canon EOS-1Ds Mark III
(Adobe Camera Raw 4.5)
11.5 10.7 9.96 8.84
Nikon D3
(Adobe Camera Raw 4.5)
11.7 11.0 10.0 8.75
Canon EOS-1D Mark III
(Adobe Camera Raw 4.5)
11.7 10.7 9.99 8.73
Sony A380
(Adobe Camera Raw 5.5)
11.8 10.9 10.1 8.62
Nikon D3000
(Adobe Camera Raw 5.5)
-- 10.8 10.1 8.61
Pentax K20D
(Adobe Camera Raw 4.5)
11.4 10.6 9.82 8.56
8.5 Stops
Nikon D300
(Adobe Camera Raw 4.3.1)
11.4 10.9 9.87 8.45
Sony A200
(Adobe Camera Raw 4.3.1)
11.6 10.4 9.82 8.43
Nikon D60
(Adobe Camera Raw 4.4.1)
11.6 10.5 9.74 8.31
Nikon D40
(Adobe Camera Raw 4.1)
11.9 10.9 9.89 8.30
Canon EOS-1Ds Mark III
(Camera JPEG)
10.9 10.2 9.71 8.23
Pentax K100D
(Adobe Camera Raw 3.6)
11.3 10.3 9.51 8.23
Pentax K200D
(Adobe Camera Raw 4.4.1)
-- 10.5 9.54 8.19
Pentax K10D
(Adobe Camera Raw 3.7)
10.6 10.0 9.29 8.19
Canon EOS 7D
(Adobe Camera Raw 5.6)
11.2 10.3 9.52 8.18
Sony A100
(Adobe Camera Raw 3.4)
11.3 10.5 9.69 8.16
Canon EOS-1Ds Mark II
(Adobe Camera Raw 3)
11.2 10.3 9.40 8.14
Canon EOS 50D
(Adobe Camera Raw 4.6)
11.2 10.5 9.49 8.06
Nikon D40x
(Camera JPEG)
10.8 10.0 9.42 8.04
Olympus E-P1
(ISO 200,
Adobe Camera Raw 5.5)
11.5 10.4 9.26 8.04
Canon Rebel XSi
(Camera JPEG)
(ALO on by default)
11.3 10.1 9.34 8.01
8.0 Stops
Fujifilm S3 Pro
(Camera JPEG)
-- 9.90 9.40 7.94
Sony A350
(Adobe Camera Raw 4.4)
11.6 10.5 9.61 7.89
Canon EOS-1D Mark III
(Camera JPEG)
-- 10.2 9.70 7.88
Canon Rebel XS
(Adobe Camera Raw 4.5)
-- 10.3 9.27 7.88
Nikon D3
(Camera JPEG)
-- -- -- 7.87
Canon Digital Rebel XTi
(Adobe Camera Raw 3.6)
10.8 9.88 9.18 7.84
Canon EOS 5D
(Adobe Camera Raw 3)
11.0 10.4 9.21 7.83
Nikon D90
(Camera JPEG)
-- -- -- 7.77
Panasonic DMC-GH1
(Adobe Camera Raw 5.4b)
9.88 -- 9.30 7.76
Canon Rebel T1i
(Adobe Camera Raw 5.4b)
11.2 10.2 9.16 7.73
Pentax K-7
(Adobe Camera Raw 5.4)
10.6 9.93 9.07 7.73
Canon EOS 40D
(Adobe Camera Raw 4.2)
11.2 10.1 9.26 7.72
Panasonic DMC-GH1
(Camera JPEG)
8.77 -- -- 7.70
Canon Rebel XSi
(Adobe Camera Raw 4.4.1)
10.6 9.95 9.10 7.68
Canon EOS 50D
(Camera JPEG)
(ALO STD by default)
-- -- 8.90 7.68
Nikon D700
(Camera JPEG)
-- -- 9.05 7.67
Canon 5D Mark II
(Camera JPEG)
(ALO STD by default)
10.6 9.68 8.98 7.66
Nikon D5000
(Camera JPEG)
-- -- 8.96 7.65
Canon EOS-5D
(Camera JPEG)
10.2 9.68 8.82 7.65
Olympus E-3
(Adobe Camera Raw 4.3)
10.3 10.1 9.29 7.64
Nikon D60
(Camera JPEG)
10.5 9.62 8.89 7.62
Nikon D200
(Adobe Camera Raw 3)
10.6 9.65 8.96 7.61
Canon 7D
(Camera JPEG)
(ALO STD by default)
-- 9.70 8.54 7.54
Nikon D80
(Adobe Camera Raw 3.6)
11.1 10.4 9.42 7.51
7.5 Stops
Nikon D300S
(Camera JPEG)
-- -- -- 7.49
Olympus E-500
(Adobe Camera Raw 3)
10.7 9.97 8.90 7.46
Olympus E-510
(Adobe Camera Raw 4.1)
10.0 9.43 8.64 7.46
Pentax K10D
(Camera JPEG)
-- 9.49 8.88 7.44
Nikon D300
(Camera JPEG)
-- -- 8.70 7.44
Olympus E-420
(Adobe Camera Raw 4.1.1)
10.0 9.61 8.65 7.44
Canon Rebel T1i
(Camera JPEG)
(ALO=STD by default)
11.3 10.1 9.34 7.43
Nikon D2Xs
(Adobe Camera Raw 3.6)
10.6 9.90 8.93 7.42
Canon EOS 40D
(Camera JPEG)
10.6 9.52 8.78 7.42
Nikon D3X
(Camera JPEG)
-- -- -- 7.37
Nikon D50
(Camera JPEG)
10.7 9.93 8.70 7.36
Sony A380
(Camera JPEG)
(DRO Standard by default)
-- 9.54 8.84 7.32
Panasonic DMC-G1
(Adobe Camera Raw 5.2)
10.7 9.78 8.70 7.32
Nikon D3000
(Camera JPEG)
10.2 9.64 8.69 7.31
Sony A900
(Camera JPEG)
(DRO off by default )
10.2 9.75 8.49 7.31
Sony A330
(Camera JPEG)
(DRO Standard by default)
10.1 9.37 8.59 7.30
Sony A200
(Camera JPEG)
(DRO on by default)
10.4 9.43 8.91 7.29
Canon EOS 20D
(Camera JPEG)
10.3 9.66 8.85 7.29
Canon EOS 30D
(Camera JPEG)
10.3 9.50 8.57 7.29
Nikon D40
(Camera JPEG)
10.4 9.80 8.89 7.28
Sony A230
(Camera JPEG)
(DRO Standard by default)
10.1 9.51 8.51 7.26
Sony A900
(Camera JPEG)
(DRO on)
10.1 9.76 8.47 7.26
Canon Rebel XS
(Camera JPEG)
10.3 9.4 8.61 7.22
Olympus E-520
(Adobe Camera Raw 4.5)
11.0 9.46 8.70 7.20
Sony A350
(Camera JPEG)
(DRO on by default)
10.3 9.55 8.85 7.19
Pentax K-x
Camera JPEG
9.99 8.94 8.31 7.18
Panasonic DMC-GF1
(Adobe Camera Raw 5.5)
10.2 9.62 8.62 7.16
Nikon D80
(Camera JPEG)
10.1 9.43 8.48 7.12
Canon Digital Rebel XT
(Camera JPEG)
10.3 9.51 8.61 7.11
Nikon D200
(Camera JPEG)
-- 9.07 8.36 7.11
Olympus E-300
(Camera JPEG)
10.8 9.26 8.48 7.07
Olympus E-410
(Adobe Camera Raw 4.1)
10.2 9.40 8.24 7.05
Olympus E-500
(Camera JPEG)
10.0 9.14 8.16 7.05
Canon Digital Rebel XTi
(Camera JPEG)
9.83 9.10 8.27 7.04
Canon EOS-1Ds Mark II
(Camera JPEG)
10.3 9.38 8.60 7.04
Panasonic DMC-G1
(Camera JPEG)
-- 9.33 8.52 7.03
Pentax K200D
(Camera JPEG)
-- 9.50 8.30 7.01
7.0 Stops
Panasonic DMC-GF1
(Camera JPEG)
-- 9.33 8.44 6.99
Canon Digital Rebel
(Camera JPEG)
10.1 9.11 8.47 6.97
Nikon D2Xs
(Camera JPEG)
9.82 8.98 8.23 6.97
Panasonic DMC-L10
(Adobe Camera Raw 4.2)
10.4 9.34 8.48 6.91
Sigma DP1
(Camera JPEG)
-- 8.95 8.13 6.91
Pentax *istDs
(Camera JPEG)
10.2 10.0 8.87 6.90
Sony A100
(Camera JPEG)
10.2 9.24 8.39 6.89
Pentax K100D
(Camera JPEG)
10.3 9.30 8.39 6.73
Pentax K20D
(Camera JPEG)
10.2 9.21 8.09 6.66
Pentax K-7
(Camera JPEG)
9.59 8.87 8.03 6.54
6.5 Stops
Nikon D2x
(Camera JPEG)
-- 8.93 7.75 6.43
Olympus E-3
(Camera JPEG)
9.32 9.06 8.50 6.42
Panasonic DMC-L10
(Camera JPEG)
-- 8.94 8.00 6.38
Olympus E-420
(Camera JPEG)
9.18 8.82 7.93 6.37
6.0 Stops
Olympus E-410
(Camera JPEG)
-- -- 7.60 5.99
Nikon D70s
(Camera JPEG)
9.84 8.69 7.46 5.85
Nikon D70
(Camera JPEG)
9.81 8.76 7.58 5.84
Olympus E-520
(Camera JPEG)
9.32 8.68 7.74 5.74
Olympus E-P1
(Camera JPEG,
Gradation = Normal)
-- 8.85 7.74 5.47

As mentioned previously, when comparing the Canon EOS 7D to the rest of the field, its dynamic range in camera-produced JPEGs as well as ACR processed RAW files is about in line with competing models. Its higher-than-average resolution for an APS-C sensor results in slightly higher noise levels than most of the competition, which in turn limits the Imatest score at the highest quality levels, though total dynamic range scores are quite good.


Canon EOS 7D Resolution Chart Test Results

The chart above shows consolidated results from spatial frequency response measurements in both the horizontal and vertical axes. The "MTF 50" numbers tend to correlate best with visual perceptions of sharpness, so those are what we focus on here. The uncorrected resolution figures are 2,208 line widths per picture height in the horizontal direction (corresponding to the vertically-oriented edge), and 2,142 lines along the vertical axis (corresponding to the horizontally-oriented edge), for a combined average of 2,175 LW/PH. Correcting to a "standardized" sharpening with a one-pixel radius reduced the resolution score by only a bit, for an average of 2,134 LW/PH. The numbers are somewhat lower than we'd expect for an 18-megapixel APS-C SLR, but still good.

To see what's going on, refer to the plots below, which show the actual edge profiles for both horizontal and vertical edges, in both their original and corrected forms. Here, you can see that an almost ideal amount of in-camera sharpening is applied in the horizontal direction (Imatest reported oversharpening by only 2.18%), while in the vertical direction, Imatest reports oversharpening of only 0.37%. This is why standardized sharpening actually reduced the 7D's MTF 50 numbers slightly.

These are excellent results for in-camera JPEGs. Still, (as is almost always the case), you'll extract the most detail from the Canon EOS 7D's images by careful processing of its .CR2 RAW files.

 

Note: We don't feature SFR-based LW/PH resolution numbers more prominently in our reviews (eg, outside the Imatest pages) because we've found that they're *very* sensitive to minor differences in in-camera image processing. Relatively small changes in the amount of in-camera sharpening can have a large effect on the resulting resolution numbers. Imatest attempts to compensate for this by adjusting to a "standard' sharpening, but this approach can't completely undo what happens inside the cameras, and so often gives inconsistent results. Sometimes the "standardized" sharpening happens to just match the shape of the edge profile with the in-camera sharpening applied, and you'll get wildly high results. At other times, it will tend to correct in the opposite direction. Unfortunately, ignoring the in-camera sharpening entirely can result in even greater discrepancies, particularly between models from different manufacturers. Turning off sharpening in the camera may or may not fully eliminate the sharpening, so simply turning off sharpening in the camera JPEGs isn't a reliable solution. It also wouldn't be the way most people shoot the cameras. We could process RAW files with no sharpening, but then that'd only suit the people working primarily or exclusively from RAW, and would open another can of worms as to what RAW converter was used, etc, etc.

The bottom line is that numbers for resolution only take you so far. Detail handling and edge acuity are very complex issues; ones that don't easily boil down to a single number. The best approach is to simply look look at the broad array of standardized test shots we take with each camera, to the point of downloading and printing them with whatever processing you'd use if you owned the camera and shot with it. See how the differences stack up for you visually, and make your decision on that, rather than on abstract resolution numbers.

 



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