Nikon D300 Imatest Results

Nikon D300 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 D300:

The Nikon D300 showed good color accuracy, though with saturation levels a little higher than competing models. Hue accuracy was quite good, with most of the hue shift occurring in the cyans, sky blues, reds and oranges. Average saturation was 108.9% (oversaturated by 8.9%, mostly in the reds, blues and some greens). Average "delta-C" color error was only 5.21 after correction for saturation, which is pretty 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.) All in all, a very good color response for an SLR. Mouse over the links below the illustration above to compare results with competing models.

Using the Adobe RGB color space (which provides a much wider gamut, or range of colors that can be expressed), the Nikon D300 delivers more highly saturated color, with an average saturation-corrected hue error of 5.61 "delta-C" units, and average saturation of 114.7%. Again, mouse over the links below the illustration above to compare results with competing models.

This image shows how the Nikon D300 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 very good hue accuracy, as well as a contrast curve that results in moderate overexposure of some of the highest-saturation swatches.

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 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 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 Canon EOS-1Ds Mark II, which produced remarkably fine-grained image noise, even at very high ISOs.

Here, we can see why ISO 100 is treated as a "LO" extension of the normal ISO range for the D300, as low frequency color noise levels are actually higher than at ISO 200. Below is the plot for ISO 200.

The D300's noise performance at low ISO (100 & 200) is pretty similar to much of its competition, and the differences between it and the earlier D200 in this range are relatively minor. It is interesting to note though, that the high-frequency end of the noise spectrum tapers off to a higher level than that of the D200 (a noise power of perhaps 0.35, vs about 0.21 in the earlier camera). This points to Nikon having shaped the noise spectrum to favor higher frequencies more than previously. The red-channel noise is considerably higher at low frequencies than the other channels, but we've seen this recently in the Canon 40D as well. That said, the overall noise levels here are so low that these fine details of noise spectra really amount to hair-splitting.

Here's the same set of noise data at ISO 3,200. It's hard to tell because of the change in scale, but the Noise Spectrum graph looks to be shifted a bit more toward the left-hand, lower-frequency side than it was at ISO 200, further coarsening the "grain" of the image noise patterns, but it's still a fairly gentle slope. Noise-reduction is also doing a good job of keep chroma noise down, as we can see from the R, G and B lines of the chart, although lower frequency components are more pronounced.

It's interesting to look closely at the D300's shots and see what those very low-frequency bumps in the red and blue noise spectra correspond to. We frequently look at the Still Life target when judging subtle image noise, looking between the Fiddler's Elbow beer and Mas Portell olive oil bottles. In the D300's ISO 3,200 shot, there's surprisingly little chroma noise there, but slight "undulations" in the color channels can be seen. (Try boosting the color saturation in Photoshop, to make the chroma noise more apparent.) It turns out that the (very slight) red and blue blotches seem to span areas about 20 pixels wide. Their amplitude is so low and the change in coloration so slight that they're all but invisible. All in all, a very nice job of "noise shaping."

Comparing just the luminance portion of this curve (the black line) with that from the D200 shows much more high-frequency content in the D300's image, as its curve is much flatter, and it bottoms out at a much higher level on the high-frequency side of the graph. This is borne out by examination of the D300's high-ISO images, which show finer "grain" in the noise than did the D200. (Overall, Nikon's claim that the D300's ISO noise is a full stop lower than that of the D200 seems well-supported by our data and test images: The D300's shots at ISO 3,200 look a lot like the D200's at 1,600. - Although the D300 does a better job of retaining subtle detail at ISO 3,200 than the D200 did at 1,600.)

Here's the same set of noise data at ISO 6,400. Very similar to ISO 3,200, but with slightly more area under the lower frequency portion of the graph.

This chart compares the Nikon D300'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. For example, take a look at the results for the Nikon D200. While the magnitude of its image noise is lower than essentially all of its competition, the dominance of low spatial frequencies gives it a coarser and therefore much more visible grain. In the case of the Nikon D300, the magnitude of the image noise starts out the same as most of the APS-C sized sensor competition at ISO 100, then increases at a faster rate until ISO 800, where fairly aggressive noise reduction kicks in, then remains lower between ISO800 and 3200. At ISO 6400, it increases above the Sony A700, the only other camera in this group with an ISO 6400 setting. (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.) Where the D300 excels though, is in keeping its noise energy at higher spatial frequencies (producing a finer "grain" structure), and in managing to hold onto surprising amounts of subtle subject detail at very high ISOs.

Nikon D300 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 D300 with a nominally-exposed density step target (Stouffer 4110), and the D300's contrast setting at its default position.

These are excellent numbers for a current-model DSLR, well in the upper range of cameras we've tested. The tone curve shows excellent gradation in highlights, but the shadow end trails off more abruptly. This can be seen when closely inspecting shots captured by the D300, where detail is held very nicely in strong highlights, but somewhat less so in the deepest shadows.

Processing the D300's RAW (NEF) files through Adobe Camera Raw (ACR) version 4.3.1 improved dynamic range by almost a full stop. Results were similar with both ACR's automatic settings and when fiddling with the sliders manually. (Do note though, that the level of manipulation done to achieve the results above will result in severe color artifacts on color images: This level of dynamic range is really only achievable on monochrome images.)

Dynamic Range, the bottom line:

The net result was that the D300 came in ahead of most other current DSLR models, although the margin from some of its closest competition (the Canon EOS-40D) was negligibly small. We were able to eke out considerably greater dynamic range via Adobe Camera Raw, but as always, it must be pointed out that the manipulations performed to achieve that are really only applicable to monochrome subjects: If you pull back that much data from RAW files, you'll inevitably end up getting color artifacts due to saturated sensor channels.

To get some perspective, here's a summary of the Nikon D300'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 d-SLRs, 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. I was surprised to see the analytical results place the Olympus EVOLT as highly as they did, given that our sense of that camera's images was that they were in fact noisier than those of many other d-SLRs that we looked at. 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 D300 and D40) at a disadvantage, as their lowest or base ISO setting is 200, as compared to the ISO 100 settings available on most other models.

Nikon D300 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 1,356 line widths per picture height in the horizontal direction (corresponding to the vertically-oriented edge), and 1,394 lines along the vertical axis (corresponding to the horizontally-oriented edge), for a combined average of 1,375 LW/PH. Correcting to a "standardized" sharpening with a one-pixel radius increased both vertical and horizontal resolution rather significantly, resulting in an average of 2,450 LW/PH.

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 there is in fact very little in-camera sharpening applied (no noticeable bump at the top ends of the black curves), which explains why D300 JPEGs look a little soft at the default sharpening setting. This is good news though, for post-processing, as it means there are no artifacts to obscure fine detail or interfere with your sharpening methodology of choice.