Canon 1D Mark IV Imatest Results

Canon EOS-1D Mark IV 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 1D Mark IV:

As you'd expect the Canon EOS-1D Mark IV showed very good color accuracy, as well as fairly accurate saturation levels. Hue accuracy was quite good, with small hue shifts occurring in the aqua, cyan, reds, oranges and yellow. Average "delta-C" color error was only 4.35 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 112.1% (12.1% oversaturated), a bit more vibrant than some professional SLRs (that seems to be the trend these days), but still very good. Mouse over the links below the illustration above to compare results with other professional models.

Unlike most other cameras, the Canon 1D Mark IV delivers less 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 103.3%, which is lower than the sRGB results by 8.8%, but more true to life. Average saturation-corrected hue error was 6.71 "delta-C" units, less accurate than the sRGB result, but still not bad. Again, mouse over the links below the illustration above to compare results with other professional SLRs.

This image shows how the Canon 1D Mark IV 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 1D Mark IV's very good hue accuracy, 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 a very slightly cool color balance when using Custom white balance, with a WhiBal card as the reference. White balance is actually pretty close to ideal though (note that the examples above deliberately exaggerate the white balance error).

Mouse over the ISO links to view the graph for that ISO sensitivity. 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.

At lower ISOs, we see that the luminance curve (in black) is relatively flat, indicating the 1D Mark IV is keeping plenty of the noise energy at high frequencies, resulting in very fine noise "grain". Chrominance channels at ISO 50 through ISO 800 contain more low-frequency energy than the luminance channel, indicating some color noise "blotchiness", spanning multiple pixels. That said, the overall noise levels here are so low that noise is all but invisible except when pixel peeping at deeper mid-tones and shadows, where it is visible, but very low. At ISO 1,600 and above, the spectrum curve shifts more to the left, indicating a coarsening of the "grain". Chrominance noise tracks luminance noise much more closely at all but the lowest frequencies at higher ISOs, likely a result of the default high-ISO noise reduction working harder to suppress chroma noise, though both luminance and chroma noise are quite strong at the highest ISOs. Notice also that the total noise levels increase with ISO, as expected. (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.)

This chart compares the Canon 1D Mark IV's luminance noise performance at midtone grey density over a range of ISOs against that of other professional 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 1D Mark IV's luminance noise magnitude starts out very low at ISO 50, and continues to remain lower than most of the crop up to ISO 800, where it is about equal to the best performing camera, the Nikon D3S. At ISO 1,600, luminance noise levels are lower than its predecessor, the 1D Mark III, but a little higher than the rest of the group. At ISO 3,200, the Mark IV's luminance noise levels are significantly lower than the 1D Mark III, about the same as the Nikon D3X, and higher than the rest of its peers. The trend is similar at ISO 6,400, though the Mark IV's luminance noise is a bit lower than the D3X. At higher ISOs, the Mark IV's luminance noise levels are higher than the other two cameras capable of such high ISOs, except the Nikon D3, which is higher at ISO 25,600. Noise is significantly higher than the current high ISO champ, the Nikon D3S at ISO 6,400 and 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 1D-Mark IV offers 4 levels of high ISO noise-reduction to choose from.)


 

Canon 1D Mark IV 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 1D Mark IV with a nominally-exposed density step target (Stouffer 4110), with the camera's Highlight Tone Priority and Auto Lighting Optimization turned off, and contrast and other exposure-related settings at their default values.

These are the dynamic range results of an in-camera JPEG at ISO 50. Normally, the native base ISO results in the best score, which would be ISO 100, but the 1D Mark IV produced a better score at the highest quality level at ISO 50. Here, we can see that the tone curve shows pretty good gradation in the highlights, but the shadow end trails off rather abruptly. A sharp tail-off at the shadow end usually signals plugged shadows and lost detail in images, but the 1D Mark IV showed no such behavior at low ISOs. There's clearly more gradation at the highlight end of the tonal scale, but examining deep shadows on the 1D Mark IV's test images showed excellent detail, in all but the very darkest shadows. Total dynamic range reported is 9.38 f-stops while dynamic range at the highest quality level is 8.1 f-stops.

Here are the same results at ISO 100, the Mark IV's true base ISO. As you can see, total dynamic range is slightly better than ISO 50 (9.67 vs 9.38 f-stops), but the score at the highest quality is a bit lower (7.61 vs 8.1 f-stops). This is no surprise, since noise is slightly higher at ISO 100 vs ISO 50, especially in the shadows.

Processing the Canon 1D Mark IV"s RAW (.CR2) files through Adobe Camera Raw (ACR) version 5.7 increased dynamic range by about 0.8 f-stops at the highest quality level (8.9 f-stops), compared to the best in-camera JPEG (8.1 f-stops), while total dynamic range reported increased by over 1.5 f-stops from 9.67 to 11.2. These results were obtained by using ACR's automatic settings. Slightly better results are possible with manually tweaking, though we weren't able to improve results. 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. Also, the extreme highlight recovery being performed by ACR here would likely produce color errors in strong highlights of natural subjects. Indeed, recovered highlights in our step-chart showed a reddish tint in Photoshop.

Dynamic Range, the bottom line:

The net result was that the Canon 1D Mark IV's JPEGs scored near the top of all SLRs we've tested in Imatest's dynamic range analysis, while RAW files converted with ACR placed in the top tier. Excellent results.

To get some perspective, here's a summary of the Canon 1D Mark IV'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.

Comparing the Canon 1D Mark IV to the rest of the field, its dynamic range in camera-produced JPEGs much higher than average, even among professional models, bested only by the Canon EOS-1Ds Mark III. Adobe Camera Raw managed to boost dynamic range scores significantly, but as noted above, the extreme processing it's applying in the highlights would almost certainly result in color errors in strong highlights in highly-colored natural subjects; the actual dynamic range of the sensor is likely somewhere in between.

Canon 1D Mark IV 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 2,116 line widths per picture height in the horizontal direction (corresponding to the vertically-oriented edge), and 2,605 lines along the vertical axis (corresponding to the horizontally-oriented edge), for a combined average of 2,361 LW/PH. Correcting to a "standardized" sharpening with a one-pixel radius reduced the resolution score by quite a bit, for an average of 1,838 LW/PH, indicating that the 1D Mark IV oversharpens its JPEG images at the default setting.

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 excessive amount of in-camera sharpening is applied in the horizontal direction with Imatest reporting oversharpening by 13.8%, while in the vertical direction, Imatest reports oversharpening of 6.9%. This is why standardized sharpening reduced the Mark IV's MTF 50 numbers by so much. For best results from JPEGs, users should turn down the in-camera sharpening and sharpen images in post processing. As is almost always the case, you'll extract the most detail from the Canon 1D Mark IV images by shooting RAW and carefully processing its CR2 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.