Canon 60D Imatest Results

Canon 60D 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 60D:

As we've come to expect from Canon, the EOS 60D showed very good color accuracy, as well as fairly accurate saturation levels. Hue accuracy was much better than average, with small hue shifts occurring mainly in the cyans, reds, and oranges. Average "delta-C" color error was only 3.78 after correction for saturation, which is excellent, among the best we've tested. (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 108% (8% oversaturated), which is also very good. Mouse over the links below the illustration above to compare results with competing models.

Like most other cameras, the Canon EOS 60D 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 116.3%, which is higher than the sRGB results. Average saturation-corrected hue error was 4.93 "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.

This image shows how the Canon EOS 60D 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 60D, 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.)

The bottom row of the chart shows exaggerated white balance errors, revealing that the camera produced fairly accurate color balance using Custom white balance, with a WhiBal card as the reference.

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.

The Canon 60D does a pretty good job of keeping plenty of the luminance noise energy (indicated by the black line) at high frequencies. What little low-ISO image noise that's there is more fine-grained as a result. Chroma noise, though, is higher at lower frequencies, especially in the red channel. The overall noise levels are so low in low-ISO shots that the chroma noise in general and the red blotchiness in particular are only slightly visible when inspecting shadow areas of low ISO shots very closely.

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 60D'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 60D does a better than average job at keep chrominance noise in check, though default noise reduction does struggle with reds in areas of low contrast.

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 60D'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.)

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 60D's ISO 12,800 shots, a few bright noise pixels are evident, especially in the shadows and darker areas, however there is a huge improvement over the 50D in this regard.

This chart compares the Canon EOS 60D'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 60D's luminance noise magnitude starts out lower than the 7D's and remains lower or equal to it throughout the ISO range. Compared to its less expensive sibling, the 60D's curve closely follows the T2i's curve up to ISO 1,600, then increases to slightly higher levels. This may be an intentional tweak to keep the more pro-oriented 60D's detail levels a little higher in exchange for a touch more noise compared to the consumer-oriented T2i. Noise levels are also very similar to the Nikon D7000 up to ISO 1,600, but the Nikon shows less at higher ISOs. (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 60D offers 4 levels of high ISO noise-reduction to choose from, including "Off".)

Canon 60D 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 60D with a nominally-exposed density step target (Stouffer 4110), and the 60D's noise reduction, 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 good gradation in the highlights, but the shadow end trails off abruptly. This can be seen when closely inspecting shots captured by the 60D, where detail is held nicely in strong highlights, but somewhat less so in the deepest shadows. Total dynamic range reported is 10.5 f-stops while dynamic range at the highest quality level is 7.46 f-stops. This is about average for a modern SLR with an APS-C size sensor, and very similar to results from the Canon 7D and T2i. We didn't shoot with Highlight Tone Priority for this test, as the boost in ISO usually results in a lower Imatest score at the highest quality levels, however we would expect the highlight end of the curve to have a more gentle roll-off.

Processing the Canon EOS 60D's RAW (.CR2) files through Adobe Camera Raw (ACR) version 6.3 increased dynamic range by only about 0.29 f-stops at the highest quality level (7.75 f-stops), compared to the in-camera JPEG (7.46 f-stops), though total dynamic range reported increased by about 1.4 f-stops from 10.5 to 11.9. These results were obtained by using ACR's automatic settings, then manually tweaking from there. It's possible to get slightly better results with more 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 60D's JPEGs scored about average in Imatest's dynamic range analysis when compared against other current APS-C sensor models. ACR converted RAW files scored a little below average at the highest quality level.

To get some perspective, here's a summary of the Canon EOS 60D'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.):

Note that this test is repeatable to within 1/3 EV according to the Imatest website, so differences of less than 0.33 can be ignored.

Canon EOS 60D 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 2,210 line widths per picture height in the horizontal direction (corresponding to the vertically-oriented edge), and 2,140 lines along the vertical axis (corresponding to the horizontally-oriented edge), for a combined average of 2,175 LW/PH; almost exactly the same results we got from the 7D. Correcting to a "standardized" sharpening with a one-pixel radius reduced the resolution score by only a bit, for an average of 1,988 LW/PH. The numbers are somewhat lower than we'd expect for an 18-megapixel APS-C SLR.

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 a fairly aggressive amount of in-camera sharpening is applied in the horizontal direction (Imatest reported oversharpening by 11%), while in the vertical direction, Imatest reports oversharpening of only 0.907%. This is why standardized sharpening actually reduced the 60D's MTF 50 numbers slightly.

Given these results, power users might want to turn down in-camera sharpening, then add some sharping during post processing. As is almost always the case, you'll extract the most detail from the Canon EOS 60D'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.