Nikon D300S Imatest Results

Nikon D300S 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 D300S:

The Nikon D300S showed excellent color accuracy, as well as fairly accurate saturation levels. Hue accuracy was exceptionally good, with small hue shifts occurring in the reds, oranges and some greens and purples. The larger shifts in aqua and cyan are very common among the cameras we test; we think they're an effort to produce sky colors that look better on monitors and in print. Average "delta-C" color error was only 4.6 after correction for saturation, which is excellent. (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 110.6% (10.6% oversaturated), a bit more vibrant than some semi-pro SLRs, but still very good. Mouse over the links below the illustration above to compare results with competing models.

Like most other cameras, the Nikon D300S delivers more highly saturated colors when using the Adobe RGB color space (which provides a much wider gamut, or range of colors than can be expressed in sRGB). Average saturation was 117.1%, which is higher than the sRGB results, but saturation is about all that changed: Average saturation-corrected hue error was 4.88 "delta-C" units, slightly less accurate than the sRGB result, but still very 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 Nikon D300S 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 what the ideal color would look like if the brightness were adjusted to match the camera's tone curve, while the small rectangle shows the numerically correct color with no adjustment. This image shows the very good hue accuracy of the D300S, as well as a the commonly-employed trick of overexposing some of the highest-saturation swatches, to give an impression of "brighter" color, without actually oversaturating.

The bottom row of the chart shows exaggerated white balance errors, revealing that the camera produced a slightly cool color balance when using Custom white balance, with a WhiBal card as the reference. White balance is actually pretty close for midtone through highlight values (note that the examples above deliberately exaggerate the white balance error). It's somewhat worse in the shadows, but is also less visually apparent there.

There's a lot in this particular graph, a lot more than we have room to go into here.

In comparing these graphs with those from competing cameras, we've found that the Noise Spectrum graph at lower right is the most important in terms of how the noise appears visually and how much effect a given amount of noise has on the image. 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 total amount of noise is also obviously relevant, so we do look at the graphs in the lower left and upper right, but the noise spectrum has the most impact on how visually objectionable noise will appear.

ISO 100 is treated as a "LO" extension of the normal ISO range for the D300S, and that perhaps shows up here in that there's a lot of low-frequency energy in the red and blue channels. Overall noise levels (the upper right and lower left plots) are slightly lower than at ISO 200, though, as one would expect. Below is the plot for ISO 200.

Here's the same set of noise data at ISO 200, the D300S' native ISO. The differences between it and the earlier D300 are relatively minor. The D300S does a pretty good job at keeping luminance noise (indicated by the black line) at higher frequencies, resulting in a very fine noise "grain" at low ISOs. Like many cameras these days, the red and blue channels have significantly higher noise levels at lower frequencies. 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 still quite low.

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 and 200. 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 D300S' ISO 3,200 images. The red and blue channels' noise spectrum follows that of the luminance and green channels much more closely, a result of the default high ISO noise reduction applied, but is still higher at very low frequencies. This can be seen in high ISO images as large but subtle blotches of chroma noise, spread across multiple pixels. Overall, though, the D300S does a better job at holding a tight grain pattern than most competitors.

Total noise levels at ISO 3,200 are best described as "competitive," with the D300S performing in the same ballpark as the Canon T1i, 50D or 7D, but somewhat better than the Pentax K-7. It does better than the Canons from midtones down through the lighter shadows, but the Canons edge it in the very darkest shadow areas.

Here's the same set of noise data at ISO 6,400. The Noise Spectrum graph has shifted even further to the left, and the D300S' default noise reduction has further reduced the chroma noise to more closely follow luminance noise. Notice also 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.)

This chart compares the Nikon D300S' 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 Nikon D300S' luminance noise magnitude follows that of its predecessor, the D300, extremely closely (the values are almost identical), while remaining lower than most of the competition for all ISOs except 6,400, where it exceeds that of the Sony A700. It's interesting to note that D300S' noise magnitude is lower at ISO 800 than at ISO 400, the result of fairly aggressive default high ISO noise reduction kicking in at that point. (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 Nikon D300S offers 4 levels of high ISO noise-reduction to choose from.)


 

Nikon D300S 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 Nikon D300S with a nominally-exposed density step target (Stouffer 4110), and the D300S' contrast and other exposure-related settings at their default values.

Here, we can see that the tone curve shows excellent gradation in the highlights, but the shadow end trails off very abruptly. This can be seen when closely inspecting shots captured by the D300S, where detail is held very nicely in strong highlights, but somewhat less so in the deepest shadows. Total dynamic range reported is 9.02 f-stops while dynamic range at the highest quality level is 7.49 f-stops. The D300S does a good enough job of controlling noise in the shadows that the image quality never drops below the Medium-High level before the camera runs out of dynamic range altogether. Its dynamic range at the Medium-High and lower quality levels is thus the same as its total dynamic range of 9.02 stops. The D300's score at highest quality is very similar to those other current top-end sub-frame SLRs. Its range at the Medium-High quality level is better than most, while its total (maximum) dynamic range is noticeably lower.

Note that this test was done with Active D-Lighting disabled by default, and we didn't test the other Active D-Lighting settings as we found it made little difference to the Imatest scores. In fact, such schemes often lower the score at the highest quality level because the brightness boost in shadow areas also increase the noise.

Processing the Nikon D300S' RAW (.NEF) files through Adobe Camera Raw (ACR) version 5.5 increased dynamic range by 1.4 f-stops at the highest quality level (8.89 f-stops), compared to the in-camera JPEG (7.49 f-stops), while total dynamic range reported increased by about 2.5 f-stops from 9.02 to 11.5. These results were obtained by using ACR's automatic settings; then manually tweaking from there, so slightly better results may be possible. 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.

Dynamic Range, the bottom line:

The net result was that the Nikon D300S' JPEGs scored about average in Imatest's dynamic range analysis when compared against other current APS-C sensor models. Nikon D300S RAW files converted with ACR did much better, scoring in the top 10 cameras we've tested to date.

To get some perspective, here's a summary of the Nikon D300S' 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.):

Comparing the Nikon D300S to the rest of the field, its dynamic range in camera-produced JPEGs is about in line with competing models. Adobe Camera Raw managed to boost the DR pretty 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.

Nikon D300S 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 1,519 line widths per picture height in the horizontal direction (corresponding to the vertically-oriented edge), and 1,576 lines along the vertical axis (corresponding to the horizontally-oriented edge), for a combined average of 1,547 LW/PH. Correcting to a "standardized" sharpening with a one-pixel radius changed the resolution score by quite a bit, for an average of 2,346 LW/PH. The corrected numbers are quite good for a 12-megapixel APS-C SLR, and very similar to the results we got for the Nikon D300 (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 a very conservative amount of in-camera sharpening is applied in the horizontal direction (undersharpened by 23%), while in the vertical direction, Imatest reports undersharpening of 21.9%. This is why standardized sharpening improved the D300S' MTF 50 numbers by so much. The conservative in-camera sharpening means that camera-produced JPEGs will take unsharp masking in Photoshop or other image-editing software better than most.

These are very good results. Still, (as is almost always the case), you'll extract the most detail from the Nikon D300S' images by careful processing of its NEF RAW files.