Friday, March 29, 2013

THE SIGMA DP MERRILS AND THEIR COLORS: THE TRUTH REVEALED!

As this blog's readers might already know, last November I decided to get the Sigma DP1 Merrill & Sigma DP2 Merrill, curious to see if and how these new high-level compacts would fit in my camera bag. After using them for a week in Venice, I liked them so much that I decided to keep them: I reviewed them HERE and compared them HERE with my Sony Nex-7 (which unfortunately got sold as a result), and started waiting eagerly for the newly announced Sigma DP3 Merrill. Finally, yesterday I got the DP3M in my hands completing what is (so far at least) the Sigma DP Merrill lineup: 3 cameras covering focal lengths of 28mm, 45mm and 75mm FOV and all featuring the same APS sized, 45 Mp Foveon sensor (equal to about 30 Mp for Bayer sensors).

The DP Merrill lineup: from left to right, the DP2 Merrill (45mm), DP3 Merrill (75mm) and DP1 Merrill (28mm)

Since the release of the Sigma DP3 Merrill, the Internet has been full of contradicting reports about whether the DP3 Merrill handled colour differently - or more specifically, better - than its older brothers. Some said the DP3M's colours were very different in a better way from those generated by the DP1M / DP2M, others said there weren't any differences: no hard proof was provided, however, substantiating either claim. For sure, Sigma didn't announce any changes in camera hardware or any differences in firmware that could justify such different results, but we all know how manufacturers do change minor things for the most different reasons in a product lifetime without informing the public.

When I finally got the DP3 Merrill in my hands, I was very curious to see with my own eyes and decide by myself where things stood, leaving once and for all all the Internet noise and all these more or less substantiated claims behind. So, before even taking the camera out for a spin in the real world, I decided to try and put this issue to rest doing a quick controlled test in house.

So what's the verdict? Are there any differences in output and colour handling between the DP3 Merrill and its DP1M & DP2M brothers? More, are these differences (if any) due to hardware changes, firmware tweaking or are just due to users' different post-processing? Find out after the jump!

A couple of words about the test and its methodology first, keeping in mind that my purpose here was to compare the colours of the three DP Merrill cameras, not creating the most perfect test conditions possible: what is important is that all three cameras were examined under the exact same conditions, rather than what these conditions were.

Comparing different cameras' colour response can be tricky, due to the many variables involved; in order to remove as many of these variables as possible, I shot 3 series of pictures of my unexciting subject, a X-Rite colour chart, under flash light and using three different WB settings. I used Auto WB in the first set to see what the cameras' own ideas of colours were; I used Flash WB in the second set to see how the cameras' preset WB worked; finally, for the last set I did a spot WB in Sigma Photo Pro 5.5.1 to check the cameras' colour response using Custom WB.

I used the same exposure in manual mode for all photographs and all cameras, 1/125 @ f8 at ISO 100 so that what little daylight there was in my studio would not influence the exposure; all cameras have been updated to the latest firmware available; cameras were placed on a tripod so I could be out of the flash's way during exposures; flash was fixed on a stand slightly up and camera right, and its position didn't change between shots; cameras and tripods, on the other hand, were moved closed to and further from the target chart to compensate for the different focal lengths so that the chart would show the same magnification in each image series, to prevent having different expands of white wall between the three cameras from influencing WB / colour response; finally, images have not been cropped.

I shot RAW in AdobeRGB colour space, processed the files in Sigma Photo Pro 5.5.1 applying the exact same settings for each file: contrast +1, exposure +0.5, colour set to neutral, all other setting to zero; I then exported the files as 16bit TIFF; opened them in Photoshop CS6; added a 10, 1.2, 250 level correction to each; spot-measured the colour squares using a 31px checker to have a large enough sampling area; wrote the results as RGB values in each checker and saved the images as 8bit sRGB JPGs.

For brevity, I'll leave the interpretation of each RGB value set to you, and keep to a general analysis of the results as far as the differences in exposure and colour rendering go.

First, let's look at the Auto WB series, so we can see how differently the three cameras "see" the colours if left all by themselves under a pretty standard and "easy" light such as flash light.




EXPOSURE
It is interesting to see these three cameras showing such different sensitivity to light; exposure, light, image area captured and everything else being equal. From lower to higher sensitivity, first comes the DP1M, then the DP2M and finally the DP3M as the most sensitive to light of all. The different lens designs with the consequent different angles of incidence of light on the sensors are very likely responsible for these differences in exposure. Generally, the longer and / or the more tele-centric the lenses are, the more efficient they are at collecting light: we see that happening here when progressing from 19mm to 30mm ad finally to 50mm lenses on equal sensors.

COLOUR RENDERING
First of all, note how all three cameras get the blues when left in Auto WB; all images show a pronounced cyan cast. That aside, taking into account the small variations in exposure the RGB values output of the Sigma DP1M & DP2M are pretty much identical. On the other hand, the DP3M renders colours very differently in Auto WB, even accounting for the differences in exposure. Check the red / pink checkers, the brown, the cyan (above the black one) and the yellow / orange ones, and you will see that the balance between R, G & B is very different. In short, I'd say more R, G and less B in the red / pink and yellow / orange tones; more G in the cyan above the black; more R in the brown top left. All other colours, greys included, are pretty much the same between the three cameras.

Let's move next to the Flash WB set.




EXPOSURE
Here as well you can easily see the differences in exposure between the three cameras, with the DP3M being the most generous of all three Merrill brothers.

COLOUR RENDERING
While all three cameras still get the blues under Flash WB, definitely the DP3 Merrill behaves much better than the DP1M / DP2M here. Check the grey checkers to see how R, G & B are more balanced and actually pretty close to being neutral, weren't for a slightly weak red channel. Compared to Auto WB, under Flash WB the DP3M displays more R and less B all over the spectrum, not just for certain colours as in the previous sample set; its rendering is overall more balanced and closer to reality.

Let's now see what happens with Custom WB, using the third grey spot from the left for all the images in the set below.




EXPOSURE
The usual pattern is repeated here, with the DP3M producing brighter images than its brothers.

COLOUR RENDERING
First of all, as you can see spot WB works very well and all the greys in all images are, well, neutral grey as expected. That said, taking exposure differences into account we can spot some very minor differences not only between the DP1M / DP2M versus the DP3M, but between the DP1M and the DP2M as well. Look at the red, yellow and orange squares in the DP1M vs DP2M images and you'll notice that the DP2M outputs less B in these colours than the DP1M; look at the same squares in the DP3M vs DP2M, and you'll notice that the DP3M outputs less G than the DP2M with the result of having "redder" reds and pinks than the DP2M.

Let's now try and bring this little experiment to a conclusion.

Using Auto WB or preset WB, the DP1M / DP2M behave similarly between them, while the DP3M behaves in a quite different way (while I only tested Flash WB preset under controlled conditions, casual use of the Merrills today leads me to assume this to be a general behaviour for all presets).
Using Spot WB in Sigma Photo Pro, the DP2M and the DP3M behave very closely to each other showing only some little differences in the reds and pinks: the DP3M outputs less G in them and therefore make them look "redder" to me. All other colours are very much exactly the same. The DP1M, on the other hand, has a slightly different colour rendition, showing a little more B in the red, yellow and orange checkers.

While this test was designed to show the differences between the three Merrill cameras rather than as a test of their absolute colour accuracy, I quickly confronted the values resulting from my tests above with those provided by X-Rite as a reference Colorimetric Values for their family of targets. As evident to anyone, Auto WB is way off even under such a pretty standard light as flash; Flash WB preset is getting closer to the chart reference values with the DP3M, but is off by quite a bit with the DP1M & DP2M. Custom WB is of course the closest of all, and it would be interesting to perform a controlled test in the future to see what the DP1M, DP2M and DP3 Merrill colour behaviour is in absolute terms.

As well, even if this is not exactly colour-related, I'd like to point out once more the metering differences existing between these cameras; the DP1M has the most conservative meter of the three, the DP2M sits in the middle and the DP3M has the most generous of all. While people owning one Merrill camera only or using only one camera at a time need not to be bothered by this, it can becomes very frustrating for people shooting more than one camera side by side at the same time: these users need to remember this and compensate accordingly, because just reporting one camera's exposure to the next would result in either underexposure or overexposure, but never in consistent exposures between cameras.

To sum things up, it is clear to me that Sigma changed the colour output of the DP3 Merrill noticeably when using IN CAMERA WB and WB presets. When using CUSTOM WB in Sigma Photo Pro 5.5.1, on the other hand, the output of the three Merrills is much closer to one other: so much so that most users wouldn't notice any differences at all, and that whatever differences there are can be fixed easily enough in post-processing if one so wish.

Do I prefer the DP3 Merrill output when using Auto WB or WB Presets? Yes indeed, definitely so; I hope Sigma will bring these changes to the DP1M and DP2M as well via FW updates.

Do I think that the DP1 & DP2 Merrill are unusable for serious work, or do I think that only with the DP3 Merrill Sigma finally gave us a camera than can be used professionally with ease? No, not at all. Using Custom WB, as any serious photographer would do for critical work, all three cameras produce perfectly usable colours in my opinion, eventually using some small tweaks when needed.

OK, this is about it for today, I will post my user review of the Sigma DP3 Merrill as soon as  it's ready. In the meantime, thank you for reading so far, and stay tuned for more...

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