Nikon D60 Imatest Results

Nikon D60 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 Nikon D60:

The Nikon D60 showed pretty good color accuracy, though its average saturation is a moderately higher than that of its competition. Hue accuracy was very good, with small hue shifts occurring in many colors. Average saturation was 118% (18% oversaturated) and average "delta-C" color error was 7.28 after correction for saturation, which while not bad, isn't as good as some of the competition. (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.) Overall, a good (albeit vibrant) color response for a dSLR. Mouse over the links below the illustration above to compare results with other recent models.

Unlike most cameras, when using the Adobe RGB color space (which provides a much wider gamut, or range of colors that can be expressed), the Nikon D60 delivers less saturated color, with an average saturation of 100.9% and average saturation-corrected hue error of 5.85 "delta-C" units. An unusually accurate result overall, although there are a few more hue shifts than we'd like to see. Again, mouse over the links below the illustration above to compare results with other recent dSLRs.

This image shows how the Nikon D60 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 ideal 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 ideal color, without any luminance correction. This image shows the good hue accuracy, as well as a gamma curve that's slightly shifted toward the lower end of the tonal scale. This would lead us to think that it handled strong highlights particularly well, but under contrasty lighting, we found it tended to blow them out: Apparently the behavior here (below saturation) is different from when it actually encounters a really overexposed highlight. As part of its "bright color" aesthetic, it also overexposes highly saturated colors a bit, a fairly common tactic we've seen on many consumer-oriented cameras we've tested.

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

In comparing these graphs with those from competing cameras, I'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 champion at this was the Nikon EOS-1Ds Mark II, which produced remarkably fine-grained image noise, even at very high ISOs.

Except for the red channel, the Nikon D60 does good job of keeping the noise energy at low ISOs up at high frequencies. What little low-ISO image noise that's there is more fine-grained as a result. The red channel's noise has a large spike at very low frequencies, and in this case that actually seems to help the red channel somewhat: It's noise pattern in areas of flat tint is very soft, making it all but invisible at low ISOs. - Actually, that could be claimed for any of the noise shown here at low ISOs, it's just not evident with normal subjects at reasonable print sizes.

Here's the same set of noise data at ISO 3,200, the D60's maximum sensitivity. Here, the Noise Spectrum graph is shifted quite a bit toward 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 D60's ISO?3,200 images. The red channel is now pretty much in-line with the others, most likely the result of Nikon's default high ISO noise reduction. (Even with the default NR setting of Off (the default in the shooting menu), the D60 still performs some noise reduction at ISOs above 800.)

This chart compares the Nikon D60's noise performance over a range of ISOs against that of other cameras. While I continue to show noise plots of this sort because readers ask for them, I 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 Nikon D60's luminance noise starts out at similar levels compared to the competition, and increases at a fairly constant rate as ISO climes to 1,600, where it ends up close to the level of the Canon XSi, and slightly higher than most of the other competition. Noise magnitude increases at a higher rate to ISO 3,200 where it is much higher than the Sony A200, the only other camera in this group capable of ISO 3,200. Do keep in mind these measurements are taken with each camera set at default settings, so the shape or position of the curve could be influenced by the settings you choose to use. The Pentax K200D's plot is a good example of this. Its noise magnitude is higher than the others, but that's partly because the K200D's default contrast and sharpness settings are a bit on the high side.

One difference between the D60 and D40x is that the D60's noise reduction setting defaults to Off rather than On. The main noise plot above shows the results from the default (Off) setting. The graph immediately above shows what happens when you turn the Noise Reduction option On: the D60 more closely mimics the behavior of the D40x, but its noise levels are still a little bit higher at ISO 3,200.

Nikon D60 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 image below shows the test results from Imatest for an in-camera JPEG file from the Nikon D60 with a nominally-exposed density step target (Stouffer 4110), and the D60's contrast and D-Lighting settings at their default positions.

While not quite as good as the D40x it replaces, these are still better than average numbers compared to current-model dSLRs. We ran the same test with Active D-Lighting enabled, but found that while overall dynamic range increased to 11.2 EV, dynamic range at the highest quality level actually fell slightly to 7.46 EV, probably due to increased shadow noise from a boost in local exposure levels.

Processing the Nikon D60's RAW (.NEF) files through Adobe Camera Raw (ACR) version 4.4.1 increased total dynamic range by over one f-stop from 10.8 to 11.9, and increased dynamic range by about 2/3 stop at the highest quality level, compared to the in-camera JPEG with Active D-Lighting off. These results were obtained by using ACR's automatic settings; slightly better results may be possible by adjusting the sliders manually. It's also worth noting here is that ACR's default noise reduction settings reduced the overall red- and blue- channel noise somewhat (see the plot in the lower left-hand corner) relative to the levels in the in-camera JPEG. ACR also shifted slightly more of the noise energy into high spatial frequencies, making its residual noise even less objectionable than that found in the camera JPEGs.

Dynamic Range, the bottom line:

The net result was that the D60 performed slightly better than average for JPEG images straight from the camera, and is near the top of the pack for dynamic range from NEFs processed through ACR. An excellent performance.

To get some perspective, here's a summary of the Nikon D60'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.):

The results shown in the table are interesting. One of the first things that struck me when I initially looked at test data for a wide range of dSLRs, was that here again, purely analytical measurements don't necessarily correlate all that well with actual photographic experience. There's no question that the Fuji S3 Pro deserves its place atop the list, as its unique "SR" technology does indeed deliver a very obvious improvement in tonal range in the highlight portion of the tonal scale. On the other hand, while the Canon Rebel XSi does a good job with high-contrast subjects (thanks to its Advanced Lighting Option that's on by default), to our eyes, it doesn't compete with the S3 Pro. In the other direction, I was quite surprised to see the Nikon D2x place as low on the listings as it did, given that we found that camera's shadow detail to be little short of amazing.

One thing that's going on here though, is that we tested each camera at its lowest ISO setting, which should produce best-case noise levels. This is in fact what many photographers will be most interested in, but it does perhaps place some of the Nikons (like the D40) at a disadvantage, as their lowest ISO setting is 200, as compared to the ISO 100 settings available on most other models.

In the case of the Nikon D60, it places very well, showing higher dynamic range from its in-camera JPEGs than most cameras we've tested. In practice, we found its somewhat contrasty tone curve made it easy to lose highlights under high-contrast lighting. It appears that its excellent dynamic range comes more from its handling of deep shadows than strong highlights: Aim to underexpose slightly in high-contrast situations, and you should be pleased by the amount of tonal range the camera captures.

Nikon D60 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 I focus on here. The uncorrected resolution figures are 1,984 line widths per picture height in the horizontal direction (corresponding to the vertically-oriented edge), and 1,782 lines along the vertical axis (corresponding to the horizontally-oriented edge), for a combined average of 1,883 LW/PH. Correcting to a "standardized" sharpening with a one-pixel radius increased both vertical and horizontal resolution by quite a bit, resulting in an average of 2,256 LW/PH. This is a very good performance for a 10-megapixel camera.

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 fairly conservative in-camera sharpening is applied in the horizontal direction (according to Imatest, undersharpened by 5.49%) , and even less sharpening is applied in the vertical direction (undersharpened by 7.96%). Still, for the ultimate in sharpness, dial down the camera's internal sharpening and process the resulting images after the fact in Photoshop or other image-processing application to bring out the maximum detail without introducing sharpening artifacts.