March 2016 - colorsync-users

gamma bewilderment wrt/ Argyll’s documentation
by Uli Zappe 07 Apr '16

07 Apr '16

Hi, I’ve stumbled about the following passages in Argyll’s documentation for dispcal (http://www.argyllcms.com/doc/dispcal.html) > -g gamma Set the target response curve gamma. This is normally an exponential curve (output = input ^gamma), and defaults to 2.4 on MSWindows and Macintosh OS X 10.6 or latter and Linux/Unix (which is typical of a CRT type displays real response), and 1.8 on a Macintosh (prior to OS X 10.6). > [...] > Also note that many color spaces are encoded with, and labelled as having a gamma of approximately 2.2 (ie. sRGB, REC 709, SMPTE 240M, Macintosh OS X 10.6), but are actually intended to be displayed on a display with a typical CRT gamma of 2.4viewed in a darkened environment. This is because this 2.2 gamma is a source gamma encoding in bright viewing conditions such as a television studio, while typical display viewing conditions are quite dark by comparison, and a contrast expansion of (approx.) gamma 1.1 is desirable to make the images look as intended. There are 3 things here which I don’t understand: 1. Where do some of the default gamma values come from? In the Mac OS X 10.6 release notes (https://developer.apple.com/library/mac/releasenotes/MacOSX/WhatsNewInOSX/A…) Apple clearly stated that the gamma is now 2.2 (not 2.4, as the Argyll doc says): > Historically, the default gamma correction for Mac OS has been a value of 1.8 (a useful value for print professionals). In recent years, television, video, and web standards have all settled on a default gamma of 2.2. In OS X v10.6, the Mac moves to this common standard Later, Apple has repeatedly confirmed this. It is true that when Apple talks about gamma 2.2, they actually mean the sRGB TRC. You can verify this by looking at the OS X supplied, so-called "Generic Gray Gamma 2.2 Profile" (/System/Library/ColorSync/Profiles/Generic Gray Gamma 2.2 Profile.icc) which Apple introduced with Mac OS X 10.6 and which actually sports an sRGB TRC. But while it is true that the gamma curve *part* of an sRGB TRC is 2.4, you certainly cannot say that the sRGB TRC as a whole is “gamma 2.4". It’s either "sRGB" or (simplified) "gamma 2.2" (gamma 2.239, to be exact). That is all the more confusing since the Argyll documentation correctly reports the pre-10.6 gamma value as being 1.8, in accordance with Apple. In the same vein, the simplified gamma TRCs of REC 709 and SMPTE 240M are 1.961 and 1.932, respectively, and certainly not gamma 2.2, as the Argyll documentation says. These might be trivial documentation errors, but they gain importance with my 2 additional (following) problems. 2. Why does the documentation assume that a color appearance adjustment (= contrast expansion of gamma 1.1) is desirable by default? Video production is a very specific case, and it’s not clear from the documentation whether the "bright viewing conditions such as a television studio" refer to the recording or the editing environment. If the former, this is certainly a gross generalization, since the recording environment can be anything from a sunny beach to a dark and stormy night. If the latter, I very much doubt that a typical TV editing environment is *brighter* than the typical office environment in which a computer is typically used. But even more importantly, with a few specific exceptions, the task of color management is to preserve the colors as set by the artistic intent of the editor in the *output referred* color space, not the actual colors of the source image, anyway. So the colors of the recording environment do not really matter. Additionally, as I already wrote, video is a very specific case for color management on a computer. By far the most typical case will be that the colors of some illustration or image should be preserved on their way from the editor to the consumer. There may be all kinds of editing and viewing environments, but I fail to see how in a statistically significant way the typical viewing environment will be darker than the typical editing environment. Therefore, I don’t understand how a color appearance adjustment can be assumed to be desirable by default. 3. Why should the user care about the TRC at all in a color managed environment? This is the point that baffles me most. The whole point of color management is reliable reproduction of colors *independent of* the specific underlying technical parameters in hardware and software. This means that in a color managed environment, choosing a different gamma value for a display calibration should ideally have no visible impact *at all*, since (assuming a corresponding monitor profile) the CMM is supposed to compensate for different TRCs of source and destination. (I assume ideal hardware and software here and disregard real-world technical limitations such as hardware specs and limited bit depth, as they are not the point in this context). So if I calibrate my display to gamma 1.8 or gamma 2.4 should be completely irrelevant for the visual results I get as a user, as long as all my applications and the GUI of the operating system are color managed. On an ICC color managed computer, this means that a) using a higher gamma could not even achieve the desired contrast expansion described in point 2) above and that b) there should be no reason to recommend any specific gamma value to the user at all (whereas Argyll’s documentation makes a lot of specific recommendations). In contrast, as I understand it, the only ICC color management compatible way to achieve a color appearance adjustment (= contrast expansion, as far as the suggestions in the Argyll doc are concerned) is to build a color appearance adjusted monitor profile. Does anyone share my confusion, or can dispel it? Bye Uli _________________________________________________________________________ Uli Zappe, Christian-Morgenstern-Straße 16, D-65201 Wiesbaden, Germany http://www.ritual.org Fon: +49-700-ULIZAPPE Fax: +49-700-ZAPPEFAX _________________________________________________________________________

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RE: : gamma bewilderment: A history lesson
by Roger Breton 01 Apr '16

01 Apr '16

That's a harsh judgement, Edmund. I'd rather have the ICC than nothing. / Roger -----Original Message----- From: colorsync-users-bounces+graxx=videotron.ca(a)lists.apple.com [mailto:colorsync-users-bounces+graxx=videotron.ca@lists.apple.com] On Behalf Of edmund ronald Sent: 31 mars 2016 12:52 To: THOMAS A LIANZA <tomlianza(a)tomlianza.com> Cc: 'colorsync-users?lists. apple. com' List <colorsync-users(a)lists.apple.com> Subject: Re: : gamma bewilderment: A history lesson ICC: a sclerotic organisation obsessed by scanned imagery converted to print and controlled viewing conditions in a world where images are mostly viewed on random screens.

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Affinity Photo, calibration PA271(2) with SpectroView II
by Millers' Photography L.L.C. 31 Mar '16

31 Mar '16

Regarding v2 and v4, when profiling the PA271(2), I don’t find a choice in SpectraView II. If the choice is there, in preferences, please tell me where. I do see the choice in i1Profiler.. I don’t use i1Profiler to profile my NEC's Kind Regards David Miller, Pharm. D.

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Approximate (or exact) relationship between illuminant color temperatures?
by Ben Goren 31 Mar '16

31 Mar '16

So, I have a photographic project in mind that involves a bit of remapping between illuminants, where the relationship between two illuminants is going to be more important, I think, than the actual illuminants themselves. Specifically, I'm thinking of using a pair of strobes, one in a softbox and another hard and directional to simultaneously simulate the overhead sky and the Sun. Gelling the softbox is likely to be impractical, so the thought is to leave it at its ~6500 native temperature and heavily gel the "Sun" correspondingly. I'd white balance the final image using the same sort of approach one would for a scene in direct Sunlight with shadows -- either neutral for the primary subject, or something that leaves the subject warmish and the shadows bluish, or some other variation along those lines. The actual temperature targeted would be much visually warmer / thermally cooler than outdoors, but I'm hoping that it'd still look as if it were shot outdoors. My obvious question: how red should the "Sun" get gelled to, and how do I know that without trial and error? (I'm expecting trial and error, of course, but I want to understand what's going on.) The sky is often north of 15,000 K, and horizon sunlight can be below 5,000 K. The most naive of math would suggest that, to pair with my 6500 K "sky" I need a "Sun" with a color temperature thousands of degrees below absolute zero -- obviously absurd and obviously nowhere near the correct approach. I'm guessing instead I'd want to compare distances on the Planckian locus and figure out x, y coordinates to target. Is that reasonable? And, yes, of course -- I realize that I'm seriously oversimplifying all sorts of things and that there probably isn't an actual answer. The SPD of the strobes isn't a good match for D series illuminants, for an obvious starter. Instead, I'm hoping for some sort of "close enough" approximation. If there happens to be an actual answer, fantastic, and it'd be a good exercise for me to work through the math. But some sort of a pointer to a general vague heuristic would be welcome, too. (And, yes, I can think of some other alternatives, such as covering the ceiling with an appropriate bluish color and bouncing a strobe off of it. Other alternate suggestions are fine and welcome, but the geometry of the studio setup is likely to work least miserably with a softbox and a directional light, and only the directional light is relatively easily gelled.) Thanks, b&

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: gamma bewilderment: A history lesson
by THOMAS A LIANZA 31 Mar '16

31 Mar '16

Hi guys, I have been reading the various p*ssing contests on this list and being one of the older guys on this list who was actually there at the start of color management, and one of the strongest critics of the ICC in the beginning I thought that I would throw out some historical notes here. When I started Sequel Imaging in 1989, color management was just beginning. When I heard that Microsoft was planning to establish an RGB standard with Gamma 1.0, I got on an airplane and went for a meeting at Galactic Headquarters to point out just how embarrassing that decision would be to the company. I explained at the time there would probably two emerging color encoding schemes one with an assumed gamma of 1.8 and another with an assumed gamma of 2.2. As far as the Apple gamma 1.8 distinction, it wasn’t as stupid as many have assumed it to be. During the early period of Apple’s formation, Apple developed a lot of print and capture hardware that seamlessly worked with their platforms. All of this equipment was used at high background luminance’s and the evaluation of print to screen was made at insanely high view conditions. From a perceptual viewpoint, not a whole lot of research had been done at time, but Hunt and Stevens’ work was pretty well understood. Visual comparisons between monitor and print looked pretty good, although the color laser printer would alter a lot of that work, but the gamma 1.8 assumption worked pretty good for a long time. When Apple started making color output hardware, it was clear that there would have to be someway to calibrate the various color devices. That caused the development of ColorSync 1.0, which I can say, as an early adopter, worked well for the color reproduction products of the time viewed in uncontrolled environments at high luminance. Push forward to 1993 and we see the formation of the ICC with 8 founding members, all very large companies. HP and Microsoft were included in the mix, but I think they saw that the complexity that was being proposed would never work in the mainstream and we have, in 1996, the release of the sRGB specification. It is really important to understand that the sRGB specification is essentially an encoding specification with some peripheral documentation about the assumed viewing conditions. The sRGB spec fundamentally made color interoperable between different manufacturers and it was widely adopted very soon after introduction. In 1996, two very distinct paths of image reproduction emerged: one for consumer use(sRGB) and one for commercial use(ICC v2/v4). Between 1994 and 2001, the ICC released no fewer than 5 revisions to the specification, while the sRGB spec remained virtually unchanged, except for language changes as it moved towards ISO. As a small business owner, I was appalled at changes and the need to revise the software. Version 4.0 of the spec would finally be released as an ISO specification in 2010 roughly 17 years later. When I became Chairman of the ICC, I suggested that we move Version 4.0 into ISO (to minimize revisions) and move on to an advanced platform that could accommodate very high end activities using a full spectral workflow. This was not backward compatible with V4/V2, but it would accommodate a V4 profile in the CMM. I also directed that we provide an Open Source Reference CMM implementation to eliminate the interoperability issues of the V4 CMM’s . The latest work at the ICC has very little to do with the issues that this group focusses(obsesses) over. Now one final point about gamma and sRGB. If you take the time to actually measure the transfer function of a modern digital camera in sRGB mode, you will find that the working gamma is about 1.1-1.4 X higher than the sRGB encoding gamma. This is because the average viewer is taking the image in a high luminance environment and viewing in a low luminance environment. The print vendors tend to back this out in the print driver when working in sRGB mode. That is why a consumer level sRGB workflow actually works. In an ICC environment, a couple of things need to happen in the profile. If you take a typical sRGB camera image and print it through a simple sRGB profile and then out to the printer, it will look dark and contrasty. This has led the ICC to build a number of appearance profiles for sRGB, but I am not aware of where that work stands. The point is this: within the sRGB world, working gamma is not necessarily equal to the encoding gamma and the working gamma at different points in the process is not constant. The complexity of the ICC specification along with the multitude of revisions have lead to interoperability issues. Regards, Tom Lianza

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Nice colour work from Apple
by Martin Orpen 30 Mar '16

30 Mar '16

Was flicking through a copy of UK Vogue over Easter and saw it had an 8 page ad section for the Apple Watch. Nice paper and five colours too — the butterflies in the background have been printed very subtly in tints of metallic silver. Have they done the same in the US/European fashion magazines or was this a one-off for UK Vogue? -- Martin Orpen Idea Digital Imaging Ltd

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Affinity Photo and colorsync issue, maybe
by Millers' Photography L.L.C. 30 Mar '16

30 Mar '16

I do believe this is a colorsync issue. Well, also my issue. You know, between the ears. I am using Affinity Photo. Getting to the point, when exporting as .tiff, the .tiff opened in PS CS5 does not look like what is in the Affinity Photo application. This never happens to me when using LR 6.4 and command E to finished of the size of the image file. Academically speaking, I thought the Affinity Photo application, when exported and opened in PS CS5 would to the same thing. Even in Affinity Photo print dialogue, the pdf image does not look like the image in the Affinity Photo window. I think I’ve tried every combination of settings in Affinity Photo. I just don’t know what else to do. Appreciate everyone’s advise. Cheers, David David B. Miller, Pharm. D., member Millers’ Photography dba Spinnaker Photo Imaging Center 3809 Alabama Street Bellingham, WA 98226-4585 360 739 2826 david(a)spinnakerphotoimagingcenter.com <mailto:david@spinnakerphotoimagingcenter.com>

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Re: Colorsync-users Digest, Vol 13, Issue 89
by Millers' Photography L.L.C. 29 Mar '16

29 Mar '16

Affinity Photo, serif, does not accept there is an issue! As far as serif is concerned, I am the problem. I just really do’t think so. I have spent hours on their question forum . All sorts of exercises have suggested, none of which are successful. Image is coming to you, Ben, using wetransfer.com d From: Ben Goren <ben(a)trumpetpower.com <mailto:ben@trumpetpower.com>> Subject: Re: Colorsync-users Digest, Vol 13, Issue 88 Date: March 28, 2016 at 11:55:39 AM PDT To: "'colorsync-users?lists. apple. com' List" <colorsync-users(a)lists.apple.com <mailto:colorsync-users@lists.apple.com>> On Mar 28, 2016, at 11:44 AM, Millers' Photography L.L.C. <digitalimaging(a)dnmillerphoto.com <mailto:digitalimaging@dnmillerphoto.com>> wrote: > Ben, it is ProPhoto RGB. Um. Can you upload the file somewhere that people can have a look at it...? You might also need to contact Affinity's tech support when all is said and done.... b&

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Re: Affinity Photo and colorsync issue, maybe
by Millers' Photography L.L.C. 29 Mar '16

29 Mar '16

"Indeed, it seems to me that perhaps David's image is not tagged or that there's something else causing it to get tagged with a different profile. David...have you confirmed that the both applications think that the image is in the same space…?" b& I’m not a color scientist. You folks are. In PS CS5 I put the image file in 16 bit, ProPhoto RGB, tiff. Been doing this for years. Learned from classes, books, Bruce Fraser’s book, etc. I have been warned that ProPhoto RGB is too wide a gamut for my Epson Pro 9900 and NEC PA271(2). Sometimes I use RGB TIFF 16-bit Beta RGB from RPP 64. And, sometime when in RPP 64, I use LAB TIFF 16-bit. I will have an image file, ProPhoto RGB, 16-bit tiff in a working folder. Reopen this image file in PS CS5 (or) LR 6.4 and the image file looks the same. This very same image file, not manipulated in Affinity Photo, and opened in Affinity Photo, does not look like the image file opened in the other two applications. What should I be doing? Kind Regards, David

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Re: Colorsync-users Digest, Vol 13, Issue 90
by Millers' Photography L.L.C. 28 Mar '16

28 Mar '16

https://affinity.serif.com/forum/index.php?/topic/18821-i-am-soooo-frustrat… <https://affinity.serif.com/forum/index.php?/topic/18821-i-am-soooo-frustrat…> She can read this also d

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