Talk:Gamma correction

.55

FTA: A notable exception, until the release of Mac OS X 10.6 (Snow Leopard) in September 2009, were Macintosh computers, which encoded with a gamma of 0.55 and decoded with a gamma of 1.8.

This sentence makes it seem like the Mac just happened to use .55 accidentally, but I don't think that's historically accurate. I'm pretty sure the Mac's gamma was set to match print process, given the DTP focus of early Macs. And when you look at modern colour appearance models, their effective power factor seems close to .55 under standard conditions. 77.61.180.106 (talk) 05:43, 26 July 2023 (UTC)

gamma test image rendering on high density displays

how do we apply an "image-rendering: pixelated;" style/css to the image used for test gamma? Eesn (talk) 22:43, 25 November 2022 (UTC)

rainuré

Je suis KONE Kolot, responsable de l’entreprise 2KB spécialiser dans d'entretien ménager à Québec. Il faut dire que j’ai moi-même travaillé dans ce secteur d’activité comme étant préposé à l’entretien ménager depuis plus de 3 ans. Et vu le besoin croissant de la demande, j’ai donc décidé de lancer mon entreprise qui a aujourd’huit non seulement un ans d’existence amis aussi avec beaucoup de réalisation à son actif. 38.87.11.25 (talk) 12:00, 26 July 2023 (UTC)

1.0 gamma is just linear gamma, XYZ can use linear gamma

It is thus supported in browsers. Also stop quoting me from my gitlab comments! I never said 1.0 (in ICC profile, BTW, not gAMA) is common or even relates to PNG or JPEG. It was J2K format, unrelated. Valery Zapolodov (talk) 17:18, 26 July 2023 (UTC)

1.0 is THE WRONG VALUE when stored in any typical .png file. Stop trying to say it is correct. Also stop deleting the fact that there is no gamma value that means "put the 8 bit data unchanged into the display buffer" which is what virtually all users of 8-bit files want. Spitzak (talk) 18:15, 26 July 2023 (UTC)

Wrong. Here is PNG from dpx scan (https://forum.videohelp.com/attachments/43324-1507526652/dpx-sequence.zip), it has gAMA 1.0 and opens correctly in Chrome and Firefox. https://photos.google.com/share/AF1QipPGmNiAPrmZCZkqJUx0_NghSyyhKkBuZfCr6hVDWGkb9a5AajdfKe0-abglHoKVEA?key=ZmJlb2NQeURycEZTcFNOSnA0QjMxQzZ1NjVmVXd3 Valery Zapolodov (talk) 18:30, 26 July 2023 (UTC)

By far the biggest problem was programs writing 1.0 when the data WAS NOT 1.0 GAMMA! It does not matter if actual gamma 1.0 data displays correctly. There was an awful lot of people who thought "gamma" was the division of the actual gamma value by the display gamma value, thus 1.0. I dealt with this quite a lot and know this for a fact, and basically this meant "ignore any gamma near 1.0". It is possible that png files with this wrong gamma are disappearing nowadays so browsers don't have to do it. Also I have no idea if that image is being shown correctly, looks really dark to me (which is what would happen if "real" gamma 1.0 data is displayed without color correction on a sRGB display). Spitzak (talk) 18:41, 26 July 2023 (UTC)

No one does that. No one writes that. The ICC profile was corrupted. I edited my comments on gitlab. Valery Zapolodov (talk) 18:45, 26 July 2023 (UTC)

I edited my comment further https://gitlab.gnome.org/GNOME/gimp/-/issues/5363#note_1008599 added "Please do not use that as a cite on WIKIPEDIA!" Valery Zapolodov (talk) 18:50, 26 July 2023 (UTC)

There is such a gamma value. It is the value that must equal the transfer of display. E.g. sRGB if display is sRGB, 2.2 if display is 2.2... 1.8 if 1.8. Valery Zapolodov (talk) 18:44, 26 July 2023 (UTC)

As well as I know it, in reflection and transparency photography, the combined gamma from original scene to final visual product has to be somewhat greater than 1.0, to look right to us. Maybe up to about 1.5. I believe this is also true for electronic displays, from television CRTs up through computer LCD monitors. The human visual system is not linear, and so the system needs to correct for that. Gah4 (talk) 04:32, 21 April 2024 (UTC)

Browsers support PNG's gAMA chunk

Indeed, try to open this image in Chrome and Firefox even on android, it will show the pear, not apple https://gitlab.gnome.org/GNOME/gimp/uploads/e764b2029957401b9f99d46e3e1c6203/VhGrd.png Valery Zapolodov (talk) 18:58, 26 July 2023 (UTC)

I will add a good test with gAMA chunks. http://www.libpng.org/pub/png/colorcube/colorcube-pngs-gamma16.html Valery Zapolodov (talk) 22:21, 26 July 2023 (UTC)

Can someone find a recent summary of the current state of browser handling of gamma (or color profiles) in PNG images and HTML/CSS colors? Last time I tried running a bunch of tests on a few machines and asked browser vendors to fix their spec-noncompliant HTML/CSS color rendering was c. 2006, and my vague impression is that they still may be spec-noncompliant to this day, but I haven't tried testing any time recently. (Apple's solution about that time was to just start making their display hardware quite close to sRGB, so that if they did no color management for HTML/CSS colors they would still render roughly correctly as long as nobody used a third party display or changed the operating system display settings). It would be nice to have a clear source to cite instead of just going on the gut feeling of Wikipedians. –jacobolus (t) 04:44, 27 July 2023 (UTC)

Chrome already supports HDR (last test in https://www.wide-gamut.com/test) in AVIF and WCG in CSS since 2023 (https://css-tricks.com/the-expanding-gamut-of-color-on-the-web/ (tests) and also https://developer.chrome.com/articles/high-definition-css-color-guide/), as per CSS Color Module Level 4. Since Android 10 color managment is automatic too at least in Samsung browser. And they are already doing https://www.w3.org/TR/css-color-5/ it works perfectly on my LG C9 TV, my only monitor, and on my Galaxy S22 Ultra. Valery Zapolodov (talk) 13:38, 27 July 2023 (UTC)

There is evidence that gAMA png chunk worked in all browsers besides IE 7 as long as back in 2008. https://habr.com/ru/amp/publications/19163/ Valery Zapolodov (talk) 17:23, 27 July 2023 (UTC)

History of the Concept

I'd be interested in learning who first worked on the concept. Who named it gamma? Why gamma and not another Greek letter?

— David James, Atlanta 2600:1700:2876:78D0:6DB3:6567:68C:D699 (talk) 12:51, 20 April 2024 (UTC)

As well as I know it, and without doing any actual WP:OR, it goes back to the somewhat early days of silver halide photography. In that case, gamma corresponds to what we usually consider contrast. It is the slope of the characteristic curve, now named after Hurter and Driffield. They were working from about 1876 into the 1890's. Even more, and not so obvious, to look right to us, from original scene to a print or transparency, the gamma needs to be a little more than 1.0, maybe up to 1.4.

In addition, the beam current in a CRT is not linearly dependent on the grid-cathode voltage, but has a power law, maybe with gamma 2.5. In the vacuum tube days, it was then usual to apply an inverse gamma in the TV camera, though not quite the inverse of the CRT. That is, the camera+TV set has a combined gamma greater than 1, maybe 1.5 or so. It depends in a complicated way on the human visual system, which is not linear.

I don't know if Hurter and Driffield actually named it gamma, but it seems that they did the early work on it. Gah4 (talk) 04:28, 21 April 2024 (UTC)

Hurter and Driffield

As the article notes, gamma correction goes back to silver halide films in the 1870's and 1880's, and yet indicates that it originated with the CRT. Hurter and Driffield studied the effects on photographic films, and the characteristic curve is now commonly named after them. Gah4 (talk) 07:03, 21 April 2024 (UTC)

expansion

Reading (somewhat quickly) through both the article and all the comments in this talk page, it seems not quite mentioned enough that we don't want systems to have an overall gamma of 1. For analog photography, from light intensity into the camera, to the light reflected from a print, or viewed on a projected slide screen, what looks right to us, is a gamma somewhat higher than 1, maybe 1.3 or 1.4. Over the years, since Hurter and Driffield in the late 1800's, photographic materials were developed to look right to us. Some about photographic papers is described [03671.pdf here.] Normal contrast paper is grade 2, which can be seen on one of the graphs to have a gamma of about 2.0. Along with negatives with gamma about 0.7, the overall result is 1.4. OK, back up a little. There is some discussion in the article and talk page about gamma being, or not being, related to the human visual system: the eye. The human visual system (in the eye or brain) has a logarithmic sensitivity. We need to see with light intensity varying over about a range of 1:1000000, such that a logarithmic system is the best way. But in the end, we make them so that they look right. I suspect that the article could better explain that successive gamma transforms multiply the gamma values. As I note, a film with gamma 0.7, printed on paper with gamma 2.0 gives a result with gamma 1.4. This is a property of exponents, and so logarithms, but readers might not know that, or forget that. Note quite as early as photographic film, the right way to build television cameras and television displays, came along. It was convenient to include the gamma of CRT displays into the system, but again, the overall system gamma is about 1.3 or 1.4. That is the way we want them to look. Gah4 (talk) 09:05, 21 March 2025 (UTC)