Olympus E-510 Imatest Results

Olympus E510 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 Olympus E510:

The Olympus E510 showed good color accuracy, and a more accurate saturation level than we're accustomed to finding in consumer cameras. Hue accuracy was very good to excellent, with most of the hue shift occurring in the cyans and sky blues. Average saturation was 106.4% (oversaturated by 6.4%, mostly in the reds, a bit in some blues, and with some undersaturation in strong greens. Average "delta-E" color error was 4.8 after correction for saturation, more accurate than most cameras we test. All in all, a very good color response for an SLR, just a little off the best we've seen, although some consumers may find its more accurate saturation a little disappointing, when compared to the oversaturated color that's more typical of the genre.

This image shows how the Olympus E510 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 slight overexposure of some of the darker 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 latest version 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.) Bottom line, the Olympus E510's noise levels are low at low ISO, with a frequency spectrum that has more energy on the higher frequency (right-hand) side of the curve than do many cameras. In comparing these graphs with those from other 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. The E510's noise spectrum does a good job of keeping plenty of the noise energy at high frequencies, its low-ISO image noise is more fine-grained as a result.

Here's the same set of noise data at ISO 1,600. Here, the Noise Spectrum graph is shifted quite a bit toward the left-hand, lower-frequency side than it was at ISO 100 (note how the whole graph is piled up on the left side of the plot), coarsening the "grain" of the image noise patterns quite a bit. In the E510 though, while the frequency distribution of the noise shifts strongly to the lower range, the overall noise amplitude remains quite low, lower than that of most of the competition. (Interestingly, the E510's luminance noise levels are slightly higher than those of its sibling the E410, and its noise spectrum is slightly more shifted toward lower frequencies, producing slightly more blotchy noise patterns.) The overall effect is actually quite pleasing: ISO 1600 images are somewhat soft overall, but the grain structure for the most part manages to not appear blotchy, and a fair bit of finer subject detail is left in the images. A good job, and improvement on the earlier E500, despite the E510's higher pixel count.

This chart compares the Olympus E510'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. In the case of the Olympus E510, the magnitude of the image noise is quite low at ISO 1,600, and its images were somewhat soft, but the character of the remaining noise was fairly tight and uniform. Rather than ending up with blotchy-looking high-ISO shots with lots of lost detail in areas of subtle contrast, Olympus has traded in favor of a softer focus look overall, but with good detail retention and a fairly tight noise pattern. The blue channel is rather mottled looking, but the camera does a good job of concealing that in the full-color images. Nicely done.

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 Olympus E510 with a nominally-exposed density step target (Stouffer 4110), and the E510's contrast setting at its default position.

These are rather disappointing numbers for a current-model DSLR, but Imatest at least had a better time interpreting the data. That said though, it's apparent that image noise is the culprit in producing such drastically low dynamic range figures at the highest quality levels. On a positive note though, the E510 has more of an S-shaped tone curve though, so doesn't plug the shadow values quite as badly as does its sibling the E410. While the E510 does hold more detail in the shadows than does the E410 though, the difference is slight.

Processing the E510's RAW (ORF) files through Adobe Camera Raw (ACR) version 4.1, we had somewhat confounding results. ACR 4.1's automatic settings increased the visual dynamic range a little, but produced a very flat tone curve, with no depth to the shadows. (Basically the same behavior we encountered with the E410's RAW files.) With a little manual tweaking, we obtained much better results, and Imatest recognized more density steps, but the net results were still weak when compared to competing cameras. While weaker than other cameras though, the E510's manually-tweaked dynamic range results were a good 0.4 EV (that is, almost half an f-stop) better than those of the E410, at least when using the High and Medium-High quality thresholds for allowable noise. The results of the manual tweaking are reflected in the table below.

Dynamic Range, the bottom line:

The net result was that the E510 performed rather poorly when compared against most current DSLR models, with a full f-stop or more less dynamic range than anything currently on the market. If you're willing to work from its RAW files directly though, it will still lag the field, but not as badly.

To get some perspective, here's a summary of the Olympus E510'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 D40) at a disadvantage, as their lowest ISO setting is 200, as compared to the ISO 100 settings available on most other models.

Regardless of the positions of the other cameras though, the Olympus E510 does appear to offer rather poor dynamic range, the one notably negative mark against what is otherwise a good-performing consumer SLR. Matters improve somewhat if you take the time to process its RAW files manually, but the results are still far from stellar.

As I always say though, at the end of the day I think you have to take the figures here with a grain of salt, and look at actual images with your own eyes to see what you make of each camera's tonal range and noise levels. We'll continue performing these dynamic range tests on the digital SLRs that we review, but (just as with the laboratory resolution target results), we suggest that you not rely on them exclusively for making your purchase decisions.

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 1,473 line widths per picture height in the horizontal direction (corresponding to the vertically-oriented edge), and 1,411 lines along the vertical axis (corresponding to the horizontally-oriented edge), both on the low side. Correcting to a "standardized" sharpening with a one-pixel radius increased both vertical and horizontal resolution significantly, resulting in an average of 2,019 LW/PH, a bit below the best we've seen 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 there's only a slight in-camera sharpening applied (the slight bump at the top ends of the black curves), that the standard sharpening operator increases further. (Imatest complained that we were clipping the shadows a bit here (which would actually tend to improve the apparent edge sharpness somewhat), but that's just a consequence of the E510's high contrast. We couldn't eliminate the shadow clipping without losing the highlights.) Relative to the E410, it appears that the E510 applies very slightly less in-camera sharpening at its default setting, which should help its images take post-capture sharpening in Photoshop a bit better.