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What’s your display gamma
Hi there Resolve community
Wondering what gamma value people are using on their sdi grading displays(LCD or plasma) out of the blackmagic video cards when grading HD rec 709 ; 2.2,
2.4, 2.6 ?Thanks
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12 Replies
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Rec-709 by definition gamma is 2.2
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I’d like to know this too.
From Alexis Hurkman’s Color Correction Handbook:
2.5 This is the gamma for both SD and HD video displays as defined by the Rec. 709 standard. 2.5 is the gamma standard you should adhere to when you select a display for color correction work.
2.2 This is the default gamma setting used by all versions of Windows and Mac OS X starting with version 10.6 “Snow Leopard” and above
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From Cédric Lejeune
(Colourist group at LinkedIn, thread “Gamma Curve Setting for our critical colour evaluation monitor”)
“It mostly depends on the viewing environment. General recommendations are 2.0 in non controlled daylight lighting, 2.2 in dim light and 2.5 in dark room. In a telecine room (…) 2.3-2.4, in a brighter room where there is light from the outside 2.2. And between 25 and 35 fL depending on the lighting and the technology, more like 20 for a dark room if it’s a monitor, 16 fL (14 with LUT) for projection”.
Hope this helps.
Cheers,
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>>Rec-709 by definition gamma is 2.2
That is not the case. Rec709 defines a specification for capture and transfer (it is basically scene referred), not for display. To quote Charles Poynton:
Rec. 709 is written as if it specifies the capture and transfer characteristics of HDTV encoding – that is, as if it were scene-referred. However, in practice it is output (display) referred with the convention of a 2.4-power function display [2.35 power function in EBU recommendations]. (Rec. 709 and sRGB share the same primary chromaticities and white point chromaticity; however, sRGB is explicitly output (display) referred with an average gamma of 2.2.)
It should be added that sRGB is based on the Rec709 primaries and white point, but not display gamma as Rec709 is not a display referred specification. sRGB is intended for display of computer graphics, not video.
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Great information
Thanks everyone
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Since my book (the Color Correction Handbook) is quoted, allow me to make a slight correction, and to elaborate on Mike Most’s reply. At the time I wrote that, I was going by information regarding the inverse gamma encoded by Rec 709 compliant cameras, and so the display gamma I derived was 2.5. It was difficult to find a quoted gamma standard for Rec 709, so this is what I went with. Unfortunately for me, in light of new information it appears I was off by .1 in that section.
It has since been brought to my attention via Charles Poynton’s own open letter to the industry that there, in fact, has never been a formal display gamma standard for Rec 709, as gamma was an implicit characteristic of CRT displays that was simply “built-in.” The actual gamma employed by CRT displays is quoted by Poynton as falling between 2.3 and 2.4.
In his open letter, Poynton advocates for a published display gamma for digital broadcast displays (which by themselves have no implicit gamma) of between 2.35 and 2.4 (he seems to be hoping that SMPTE will pick one), and peak white of 80-120 cd/m(squared).
Lastly, the display gamma for projected digital cinema is 2.6 (with peak white of 48 cd/m(squared)), but that assumes a completely dark viewing environment. My understanding is that higher display gamma represents scenes better in darker environments, whereas lower display gamma represents scenes better in brighter environments (which explains sRGB’s gamma standard of 2.2 for lit office/computer environments).
With that rationale, 2.4 falls in the middle for a muted “evening living room” environment. This all reinforces the importance of a carefully controlled viewing environment, where your display settings match the characteristics of the display surround, for doing color-critical work. Personally, I hope Poynton is successful and that a single gamma standard is published, as this is a confusing topic that engenders a lot of disagreement and doubt.
http://www.alexisvanhurkman.com | http://www.correctionforcolor.com
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Charles has been advocating a defined gamma for some time now. I too wish that the industry would pay attention and come up with some sort of standard, but as Charles himself admitted to me, it’s a difficult situation now because of the different monitoring technologies being used and the vastly different monitoring environments being encountered. Digital cinema kind of has it easy, because by definition it’s always being viewed in a dark room, as you said. The defined gamma of 2.6 makes perfect sense in that environment, but it’s a much more difficult situation when we’re talking about a medium that’s viewed on everything from projection to LCD’s to plasmas to iPads.
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This thread reminds me a scene, where no less, than 3 engineers from FilmLight showed up for the Baselight installation in my facility. It took them no less, than 2 hours just to agree on the Rec-709 gamma, while setting up a display with Truelight. Inevitably, any simple question, like what gamma should be used, was answered by a long dissertation about some obscure color theories, while never answering the question at hand. The only way to get any work done was to separate them. Same here, everyone has an opinion…
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Did you separate them or got the work done ?
A slice of color…
DaVinci 8.0.1 OSX 10.7
MacPro 5.1 2×2,4 24GB
RAID0 8TB eSata 6TB
GTX 470 / GT 120
Extreme 3D+ WAVE -
In so many words, I did ask the two engineers to leave:-)
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