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  Previous versions of Tariq Gibran's message #11902419 « Sony A7R sensor gets high scores from DxOMark »


Tariq Gibran
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Re: Sony A7R sensor gets high scores from DxOMark

zhangyue wrote:
Tariq Gibran wrote:
zhangyue wrote:
sebboh wrote:
Tariq Gibran wrote:
So, if we take the RX1 (84/81) and RX1r (79/75) example I cited, your conclusion is that these two cameras are using a completely different CFA which is why they differ? I suspect there is more to it, perhaps including the AA filter as well as software tuning. Anyway, I bet the A7 with it\'s AA filter will likely have a better measurement. Incidentally, the Leica M 240 only scores 75/71 but I really don\'t hear folks talking about how bad Leica color is. I suspect the delta has to be pretty large to really matter. Per DxO:
\"In practice, the SMI for DSLRs ranges between 75 and 85, and is not very discriminating.\" Given the somewhat arbitrary nature of these scores you mentioned (and theSuede previously also mentioned), I don\'t think these scores really mean that much in practice.

i actually i hear a lot of people whining about the colors on the m240 compared to the m9. though i think maybe the m9 scores even worse?

No, in this DXO spec, actually M9 is indeed better, but not much I believe. This score won\'t tell us everything, since there is always pleasing color depend on our sensitivity but it is a good indication I will use from now on for any camera I purchase.

The difference between the M9 and M 240 measurement is a completely insignificant 1 point. Even 5-10 points is probably insignificant going by the measurement alone. I\'m going to accept what DxO says in that this measurement is not very discriminating. If it was really meaningful, they would use it in their scores...and perhaps no one would buy medium format digital backs since most are also not tops in this measurement yet do have really great color in my experience (as indicated by their Portrait Score)

The DxO score that really matters with regard to color is the Portrait/ Color Depth score. It\'s described by DxO as:

\"Portrait photography: Color Depth

Flash studio photography involves a controlled and usually maximal amount of light. Even when shooting with hand-held cameras, studio photographers rarely move from the lowest ISO setting. What matters most when shooting products or portraits is to aim for the richest color rendition.

The best image quality metric that correlates with color depth is color sensitivity. Color sensitivity indicates to what degree of subtlety color nuances can be distinguished from one another, often meaning a hit or a miss on a pantone palette. Maximum color sensitivity reports, in bits, the number of colors that the sensor is able to distinguish.

The higher the color sensitivity, the more color nuances that can be distinguished. As with dynamic range, color sensitivity is greatest when ISO speed is minimal, and falls rapidly with rising ISO settings. DxO Labs has focused on measuring only maximum color sensitivity.

A color sensitivity of 22bits is excellent, and differences below 1 bit are barely noticeable.\"

At the risk drive this off topic again, we had a discuss before on this topic. I believe MF put priority on skin tone rendering rather than absolutely color accuracy.

Most people assume that profile in software can do wonder to compensate CFA discrepancy to human eyes, which is true general speaking. but unfortunately it is not the case always.

especially at difficult or low light. Actually even with good light, I can never achieve the same green from 6D as M9. At certain case, the PP can go extreme to get target color. it is very hard to keep decent color at the same time keep decent tonality, contrast. My knowledge on this topic is quite limited, basically profile(software) can\'t truly compensate CFA (hardware) implementation. Joakim(thesuede) has given many interesting contribution on this topic.

Basically, it is more important than it looks or DXO claims like, at least for some people.

Yes, Joakim/ theSuede has addressed this color accuracy/ color response/ DxO metemerism number previously. I looked it up and I believe his conclusion on the meaningfulness of this DxO number jives with what I thought he had said. That is, it might be close to meaningless. I have highlighted the relevant text.

\"Color accuracy on the other hand, is more about matching camera color to human vision color. Here DxO uses metameric indexes as in ISO standard 17321. This uses ONLY linear math to try and match camera raw\'s to human vision. It is a measurement of how well you can fit the CFA filters to the human eye response, without resorting to spot color corrections.

But spot color corrections are part of almost any camera more advanced than a cell-phone module nowadays, so the SMI should be taken with a big lump of salt. It doesn\'t tell that much about the camera, and it certainly does not tell if the errors produced are good-natured (easy to correct with spot color corrections) or pure metameric failures that are impossible to correct.

A camera with an SMI of 80 can be WORSE than a camera with an SMI of 75, if the errors are in sensitive colors and if they are incorrigible.
But a camera with SMI80 will almost certainly be a lot better than the camera with SMI60.\"


Oct 31, 2013 at 09:58 PM

  Previous versions of Tariq Gibran's message #11902419 « Sony A7R sensor gets high scores from DxOMark »