DCamProf - a new camera profiling tool

[torger]

I realize that I actually have November 2014 CC24 chart myself, that is the new one. I have measured it myself for my own calibration but I only have a Colormunki so I don't feel fully confident of the quality to distribute it with DCamProf.

If someone has a November 2014 (or newer) CC24 and have a good pro level gear spectral measurement of it and can share I'd love to have it for inclusion.

[howardm]

v0.10.3 available for Mac OSX

[Frederic_H]

Another comparison with the C1 daylight profile : same WB, same curve (approximated), built from a CC24 target, patches measured and averaged with an i1 pro1.

Having the scene still in mind, here's what I can say

- P1 blues are too cyan, whereas dcamprof are too magenta. No real surprise here, my CC24 purple-blue and dark purple-blue are among the 3 worst for hue DE. Still, no big deal.
- P1 blues are too light, DCP ones are more realistic (I prefer/am used to the lighter ones though)
- P1 greens are too yellow, and perhaps a bit too saturated. DCP maybe lacks some.
- DCP saturated yellows (leaves) are closer to the true hue, P1 yellows are too green/lacks red. However they look a bit too saturated (not sure, hard to tell).
- the green-yellow-orange range clearly has better separation with dcamprof

The differences are actually very minimal, once the neutral operator rendering is stable enough I'll probably switch to dcamprof and design custom profile variants for my everyday use.

 

[torger]

Nice example, good demonstration of typical differences.

P1's cyan skies is a result of their warm look which is pretty global, ie there's more yellow in most of their colors.

I'm a little concerned by the sky color not being correct, it does indeed look a bit too magenta. I have noticed that differences that look pretty tiny on the CC24 can translate to very visible hue differences in the sky for example. There's some more experimentation for me to do on the colorimetric accuracy part. It seems to me that those color errors can be pretty "random", that is too magenta when generated for your camera, but better on some other. That's not nice, I'd like the look to be same on all cameras. I'm not sure yet if it is feasible to make good (in this case meaning almost perfect) matching between cameras or we have to accept that on some cameras sky may slant to magenta on some other to cyan. You can always manually tune it of course (I'd look into target adjustment feature first to get your base profile hue pushed more to cyan), but I'd ideally like that you would not have to.

It also seems like the difference in appearance between a D50-designed and a D65-designed profile may be much larger than I've thought. Again doesn't look like much on a CC24 but in a real scene you see pretty obvious differences.

The saturation level is much a matter of taste. I've tried to match appearances but chroma is hard to match, unlike hue and certainly lightness there's a quite wide span that looks sort of matching, and it probably varies a bit from day to day what I find to be the exact right level. I have recently looked at saturation levels though and find the current one pretty good, but if they are anything they would be a tiny bit too saturated, at least in the normal range. It's very easy to adjust to taste though.

I'll probably experiment some with making a "lighter blue look" config through look operators, but I probably won't push blue any lighter than it is today in the default rendering. It's already a fair bit lighter than realistic for technical reasons and I want as little subjective elements as possible in the base profile. Light blues are as common as the warm tone in bundled profiles though so I can't disregard from the desire to have them.

[Frederic_H]

The magenta sky may also be the result of the CC24 patches measurements. My i1 pro rev A is said not to be super accurate measuring high densities.

Around mid november I'll shoot different charts in better conditions and with lights closer to D50 (CC24, CCSG, IT8, CMP DT4, ...), both with the A7rII and the IQ. Should let us compare the blue behaviour on devices with different sensitivities.

[Tim Lookingbill]

The magenta sky may also be the result of the CC24 patches measurements. My i1 pro rev A is said not to be super accurate measuring high densities.

Around mid november I'll shoot different charts in better conditions and with lights closer to D50 (CC24, CCSG, IT8, CMP DT4, ...), both with the A7rII and the IQ. Should let us compare the blue behaviour on devices with different sensitivities.

That magenta sky might also be a result of the angle of light in the actual scene to your lens. I get changing sky hues shooting in similarly lit scenes depending on whether the sun is at my back, on the side or at an angle and at different times of day. I think lens coating might be adding to this as well.

[Frederic_H]

The effect is consistent, whether it's a hazy polluted summer sky or a clean spring/autumn one. The entire blue range is affected by the tint shift, from shadows to skies, where it's the most obvious.

[torger]

Skies do vary naturally from cyan to magenta depending on sun position and atmospheric conditions. LCC shots (if used here?) can also cause a slight white balance shift, but the comparison with P1 (with the same LCC) says it all I think, plus that Frederic has been very precise about color in all previous posts, so I trust his judgment.

Of what I've seen so far this does not occur in all DCamProf profiles though so the problem is probably in the base colorimetric profile. There seems to be some issues with getting blue hues right in some cases and I have not figured out all the reason for that.

[Iliah]

> I don't have a spectral reference file for the color checker passport, so you have to use only the CC24 part of it, and then you use ColorChecker.cht.

Might be worth it to mention that the paper is different between CC24 and CCP24, CCP24 being closer to semi-gloss. Spectral responses are different, as they are different between CC24 and CCSG 24-patch portion.

From profiling standpoint, there is no additional benefit from using the other portion of CCP, the one that contains white balance adjustment patches. Using it may also make shooting more difficult.

[Iliah]

I realize that I actually have November 2014 CC24 chart myself, that is the new one. I have measured it myself for my own calibration but I only have a Colormunki so I don't feel fully confident of the quality to distribute it with DCamProf.

If someone has a November 2014 (or newer) CC24 and have a good pro level gear spectral measurement of it and can share I'd love to have it for inclusion.

The sample variation between charts from different batches is sometimes very significant. The best strategy I know for those who do not have accurate measurements of the charts they use is to use the averaged results, like those reported on http://www.babelcolor.com/main_level/ColorChecker.htm or by Robin Myers in his library http://www.rmimaging.com/spectral_library/library_index.html

Goes without saying, if you can afford PatchTool or SpectraShop - get them.

[AlterEgo]

Goes without saying

a question = will you use XRGA or non XRGA measurements ? may be it is just an irrelevant difference vs the magnitude of the other errors/tolerances in the process, but still...

[Iliah]

a question = will you use XRGA or non XRGA measurements ? may be it is just an irrelevant difference vs the magnitude of the other errors/tolerances in the process, but still...

The question you are asking amounts to who's calibration standard is better, Gretag's or X-Rite's. My answer is Gretag's, and thus no XRGA if I can avoid it. Details: XRGA uses different weighting (for reds, mostly). Thus spectral data can be converted from one standard to another. dE worst case 1.4. The slightest differences in aperture and measuring geometry have more effect than the difference between Gretag and X-Rite. Gretag geometry is generally more accurate, with better conformance to 45/0. In some ways one can view XRGA as an attempt to correct for systematic geometry error.

PS: Please have a look at Tom Lianza's account on the matter http://www.color.org/events/frankfurt/Lianza_ICCFrankfurt2013instrument_compare.pdf
Few things about Mr. Lianza here: http://patents.justia.com/inventor/thomas-a-lianza

[torger]

What of D65 and D50 is the better calibration illuminant for an all-around "daylight" profile?

Adobe uses StdA and D65 in their dual-illuminant profiles.

D50 is a whole lot easier to simulate with artificial light than D65 and is thus more practical. D50 is also the reference white in the connection space of both ICCs and DCPs. D50 is also a typical print viewing standard and closer to flash light.

But is D65 still preferable if you can have it? I don't really know.

Most cameras seems to be tuned to D50, moreso than D65. With D65 a we have this blue subtraction that gets pretty strong. The difference in color reproduction between a D50 and D65 profile seems to be pretty small, at least in SSF simulations. I recently had quite a large difference in a target shooting scenario but I think that was measurement error. I haven't really had the opportunity to compare myself with own shots.

With the difference in look between D65/D50 being as small as it seems, I tend to think that maybe D50 is what we should recommend when making a general purpose profile, even a dual illuminant one, StdA + D50 instead of StdA + D65.

Anyone that has any feedback/ideas on this?

[AlterEgo]

PS: Please have a look at Tom Lianza's account on the matter http://www.color.org/events/frankfurt/Lianza_ICCFrankfurt2013instrument_compare.pdf

his presentation does not clearly say that GmB was more precise than X-Rite, but then he was X-Rite employee at the time of that presentation (even he was GmB employee before that).

[Iliah]

his presentation does not clearly say that GmB was more precise than X-Rite

His presentation says enough on the matter of the relevance, especially given his position with X-Rite at the time. The reason I linked to Mr. Lianza presentation is to give a perspective different from my own.

As to who is more precise, that was not what I was saying - I used the word "better", because of the agreement between the instruments. Generally, repeatability, long-term stability, and inter-instrument agreement are all more important than "precision". I'm off this topic

[Iliah]

In photography we use D55 and 3200K (ISO Studio Tungsten).

For "interpolation" one wants two points as far apart as possible. D65 was chosen because D75 is nearly impossible to simulate accurately while D65 is not so problematic using xenon flash; while 3200 was too "close" and impractical given the popularity of incandescent bulbs.

[AlterEgo]

His presentation says enough on the matter of the relevance, especially given his position with X-Rite at the time. The reason I linked to Mr. Lianza presentation is to give a perspective different from my own.

As to who is more precise, that was not what I was saying - I used the word "better", because of the agreement between the instruments. Generally, repeatability, long-term stability, and inter-instrument agreement are all more important than "precision". I'm off this topic

WAIT, WAIT ! you said = "Gretag geometry is generally more accurate, with better conformance to 45/0", which a regular person can interpret as "more precise", is it not ?

as for "repeatability, long-term stability, and inter-instrument agreement are all more important than "precision"" - for example somebody has one instrument and that person is facing a choice - use XRGA or non XRGA data - something has to be closer to some magical NIST grade everything instrument... it is not about corporate issues with 2 lines of "legacy" instruments producing the data that now that both lines under one roof needs to be in some agreement within small dEwhatever and so XRGA adjustments were a solution (and X-Rite being a surviving company it seems natural /selfish/ that more adjustments were to GmB than to own X-Rite instuments)...

[Iliah]

> somebody has one instrument and that person is facing a choice - use XRGA or non XRGA data

It is not a real choice. It does not matter which standard you use.

[AlterEgo]

> somebody has one instrument and that person is facing a choice - use XRGA or non XRGA data

It is not a real choice. It does not matter which standard you use.

that's difficult to digest for the guts when the adjustments are quit big for non X-Rite legacy instruments (and allegedly consistent across the instruments of the same model)

[AlterEgo]

In photography we use D55 and 3200K (ISO Studio Tungsten).

For "interpolation" one wants two points as far apart as possible. D65 was chosen because D75 is nearly impossible to simulate accurately while D65 is not so problematic using xenon flash; while 3200 was too "close" and impractical given the popularity of incandescent bulbs.

with CMF/SSF data then it is logical to create for ACR/LR a dual illuminant DCP/DNG profile with "A" (or even lower) and D75 (or even further up), as you do not really illuminate any real target with any actual light, no ?