Gamma values used on your systems?
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end-to-end gamma = [camera gamma]*[display gamma]
Camera gamma has a 0.45 exponent but is simplified to 0.51(correction thanks to Andrewfee see his post below)
The highlights are effectively gamma 0.5, going from highlights to shadows the camera goes from 0.5 to 1.0 gamma, and at the same time the camera gain factor slowly increases from 1 to 4.5.
Reference monitors use during mastering use gamma 2.2 (PAL uses 2.35). But consumers are assumed to be using crt gamma 2.5 (PAL is mastered to look acceptable 2.2 to 2.5). Color might look best at 2.2 (PAL 2.35), but should look ok at 2.5, using gamma higher than 2.5 may result in problems with color on some material.
Perception of contrast is effected by the viewing condition surround effect so different gamma is usually recommended for different viewing conditions.
Gamma of 2.5 for dim surround conditions, dim is defined as being between 0% and 20% of the luminance of white in the image).
Gamma of 2 for bright surround conditions
Gamma of 3 for dark surround conditions
Video gamma is used in tv, dvd, blu-ray, etc... including for films. High gamma = more contrast in lighter part of image, less contrast in darker part. Low gamma = more contrast in darker part of image, less contrast in brighter part. The transition point between raised and lowered contrast is in the middle intensitys, not hidden in near black. Always above middle 18% grey (perceived as middle 50% brightness). The average image brightness will also be lower with higher gamma. So it comes down to personal choice visibility of shadow detail and a brighter image vs more image depth in bright scenes.
Also video has increased color saturation over film, because expected to be displayed on bright crt. Gamma effects color saturation and hue as well. As gamma is increased, dark colors at the bottom end of the gamma curve get dimmer, while brighter colors at the top end of the gamma curve get brighter, so a mix of colors with each at different points in the gamma curve, shift in ratio/proption to each other, the color mix gets more saturated since the lowest out of the rgb colors determines how much white - desaturation is present, and the hue shifts towards the color highest in the mix.
Film gamma is used only in commercial cinemas, not consumer versions like dvd or blu-ray, it uses a lazy s-curve. The s-curve transition point is darker, and gets darker the less gamma is increased, well below middle grey, 11% grey at most. The middle point gamma is typically 3.0. So for film higher gamma = more contrast, lower gamma = lower contrast. Sadly dvds, blu-rays are remastered for video altering their gamma and color so may not look acceptable displayed using film gamma that would otherwise be better for home cinema.
Camera gamma has a 0.45 exponent but is simplified to 0.51(correction thanks to Andrewfee see his post below)
The highlights are effectively gamma 0.5, going from highlights to shadows the camera goes from 0.5 to 1.0 gamma, and at the same time the camera gain factor slowly increases from 1 to 4.5.
Reference monitors use during mastering use gamma 2.2 (PAL uses 2.35). But consumers are assumed to be using crt gamma 2.5 (PAL is mastered to look acceptable 2.2 to 2.5). Color might look best at 2.2 (PAL 2.35), but should look ok at 2.5, using gamma higher than 2.5 may result in problems with color on some material.
Perception of contrast is effected by the viewing condition surround effect so different gamma is usually recommended for different viewing conditions.
Gamma of 2.5 for dim surround conditions, dim is defined as being between 0% and 20% of the luminance of white in the image).
Gamma of 2 for bright surround conditions
Gamma of 3 for dark surround conditions
Video gamma is used in tv, dvd, blu-ray, etc... including for films. High gamma = more contrast in lighter part of image, less contrast in darker part. Low gamma = more contrast in darker part of image, less contrast in brighter part. The transition point between raised and lowered contrast is in the middle intensitys, not hidden in near black. Always above middle 18% grey (perceived as middle 50% brightness). The average image brightness will also be lower with higher gamma. So it comes down to personal choice visibility of shadow detail and a brighter image vs more image depth in bright scenes.
Also video has increased color saturation over film, because expected to be displayed on bright crt. Gamma effects color saturation and hue as well. As gamma is increased, dark colors at the bottom end of the gamma curve get dimmer, while brighter colors at the top end of the gamma curve get brighter, so a mix of colors with each at different points in the gamma curve, shift in ratio/proption to each other, the color mix gets more saturated since the lowest out of the rgb colors determines how much white - desaturation is present, and the hue shifts towards the color highest in the mix.
Film gamma is used only in commercial cinemas, not consumer versions like dvd or blu-ray, it uses a lazy s-curve. The s-curve transition point is darker, and gets darker the less gamma is increased, well below middle grey, 11% grey at most. The middle point gamma is typically 3.0. So for film higher gamma = more contrast, lower gamma = lower contrast. Sadly dvds, blu-rays are remastered for video altering their gamma and color so may not look acceptable displayed using film gamma that would otherwise be better for home cinema.
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20,735 Posts
I tweaked my CRTs down to about 2.3. With higher ANSI CR capabilities, and enough on/off CR, I prefer 2.3-2.5ish. Many people are under the wrong impression that 2.2 is the standard gamma, when it is not. I think anywhere between 2.2-2.5 is appropriate, depending on viewing conditions, display, and user preference.
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1,236 Posts
I prefer to tweak my gamma to be lower at the low brightness range and progressing to higher gamma at higher brightness levels. I use 2.0-2.1 at the low end gradually transitioning to 2.4-2.5 at the higher brightness levels. I use a Lumagen RadianceXE to shape the gamma curve.
FWIW practically 100% (DVD/Blu ray) of motion picture releases are NOT engineered with the standard ITU-R 709 pre-emphasis.
The only thing in the post production chain that is Rec 709 is the video monitor the colorist was referencing. Until recently this was an industry standard Sony or Ikegami direct view CRT. This monitor (~$25K) was designed by the manufacturer to have a ruler flat 2.20 (OETF) transfer function all the way down to 1% of reference white "when calibrated".
The only thing in the post production chain that is Rec 709 is the video monitor the colorist was referencing. Until recently this was an industry standard Sony or Ikegami direct view CRT. This monitor (~$25K) was designed by the manufacturer to have a ruler flat 2.20 (OETF) transfer function all the way down to 1% of reference white "when calibrated".
andrewfee
"If you're simplifying it, camera gamma is 1/0.51, not 1/0.45"
Ok thanks, how do you figure out what is simplifies to. I have seen it refered to before as being simplified to 0.5, but do not understand how you get the simplified figure, I guess it is what ever plots closest to it on a graph.
Craigo87 & Mark_A_W
With your end-to-end gamma figures, are you counting camera/source gamma as 0.45 or 0.51 ?
Citation4444
"I prefer to tweak my gamma to be lower at the low brightness range and progressing to higher gamma at higher brightness levels"
I too prefer a tweaked gamma curve. I have a dlp projector so guess I should not really be posting here, using a sony dvd recorder I currently end up with a odd shape, about gamma 1.5 at 0-20, gamma 2.8 at 20-40, gamma 2.5 at 40-60, gamma 3.1 at 60-80, gamma 2.1 at 80-100. So a lumpy s-curve, still it looks better than a normal 2.2 gamma curve which is the highest gamma curve the projector can manage on its own.
tbrunet
"FWIW practically 100% (DVD/Blu ray) of motion picture releases are NOT engineered with the standard ITU-R 709 pre-emphasis."
You lost me, are you saying only the color is altered when it is remastered. No change to gamma pre-emphasis from the cinema lazy s-curve gamma?
"If you're simplifying it, camera gamma is 1/0.51, not 1/0.45"
Ok thanks, how do you figure out what is simplifies to. I have seen it refered to before as being simplified to 0.5, but do not understand how you get the simplified figure, I guess it is what ever plots closest to it on a graph.
Craigo87 & Mark_A_W
With your end-to-end gamma figures, are you counting camera/source gamma as 0.45 or 0.51 ?
Citation4444
"I prefer to tweak my gamma to be lower at the low brightness range and progressing to higher gamma at higher brightness levels"
I too prefer a tweaked gamma curve. I have a dlp projector so guess I should not really be posting here, using a sony dvd recorder I currently end up with a odd shape, about gamma 1.5 at 0-20, gamma 2.8 at 20-40, gamma 2.5 at 40-60, gamma 3.1 at 60-80, gamma 2.1 at 80-100. So a lumpy s-curve, still it looks better than a normal 2.2 gamma curve which is the highest gamma curve the projector can manage on its own.
tbrunet
"FWIW practically 100% (DVD/Blu ray) of motion picture releases are NOT engineered with the standard ITU-R 709 pre-emphasis."
You lost me, are you saying only the color is altered when it is remastered. No change to gamma pre-emphasis from the cinema lazy s-curve gamma?
The pre-emphasis is aka "gamma correction". No two colorist use the same emphasis.
SMPTE industry standard ITU-R Rec 709 gamma is rarely used in capturing (film or digital video) the image nor is it adhered to in the production phase.
Gamma itself is subjective.
The pre-emphasis is aka "gamma correction". No two colorist use the same emphasis.
SMPTE industry standard ITU-R Rec 709 gamma is rarely used in capturing (film or digital video) the image nor is it adhered to in the production phase.
Gamma itself is subjective.
That doesn't match up to what the EBU and ARIB say. The EBU's measurements have shown that a CRT's native' gamma is 2.35. (not 2.5 or 2.2 as some people believe)
The ARIB's measurements of Sony/Ikegami monitors showed that the gamma value is dependant on black level (0.1cd/m² ≈2.2, 0.01cd/m² ≈2.4) and that they no not follow a power curve all the way down to black:
From ARIB TR-B28 v1.1 , page 95 in the PDF.
It's mentioned in a few EBU technical documents, but yes it's basically what plots closest to it on a graph.
The problem is that the Rec.709 curve (camera gamma) includes an exponent of 0.45.
For whatever reason, many people simplify this by ignoring the rest of the function and use 1/0.45, when the actual equivalent simplified curve is 1/0.51.
That doesn't match up to what the EBU and ARIB say. The EBU's measurements have shown that a CRT's native' gamma is 2.35. (not 2.5 or 2.2 as some people believe)
The ARIB's measurements of Sony/Ikegami monitors showed that the gamma value is dependant on black level (0.1cd/m² ≈2.2, 0.01cd/m² ≈2.4) and that they no not follow a power curve all the way down to black:
From ARIB TR-B28 v1.1 , page 95 in the PDF.
It's mentioned in a few EBU technical documents, but yes it's basically what plots closest to it on a graph.
The problem is that the Rec.709 curve (camera gamma) includes an exponent of 0.45.
For whatever reason, many people simplify this by ignoring the rest of the function and use 1/0.45, when the actual equivalent simplified curve is 1/0.51.
Great an industry "professional" including the manufacturer (Ikegami and Sony) in this case don't know how to design nor measure a display?? The info below is based on comprehensive laboratory measurements and analysis using the advanced DisplayMate Multimedia Editions together with a Spectroradiometer. The articles are written by DisplayMate Technologies President, Dr. Raymond Soneira.
http://www.displaymate.com/ShootOut_Part_2.htm
"Television, DVD, Web and computer based photographic content are generally color balanced on professional CRT studio monitors that are electronically adjusted to have a standard Gamma of 2.20, so you’ll get the most accurate images if your display also has this value."
"The Gamma for the Sony CRT agrees perfectly with the 2.20 standard value. (CRT monitors from Ikegami, another major brand of professional studio monitors, also have a Gamma of 2.20 according to their Director of Engineering.)"
Great an industry "professional" including the manufacturer (Ikegami and Sony) in this case don't know how to design nor measure a display?? The info below is based on comprehensive laboratory measurements and analysis using the advanced DisplayMate Multimedia Editions together with a Spectroradiometer. The articles are written by DisplayMate Technologies President, Dr. Raymond Soneira.
http://www.displaymate.com/ShootOut_Part_2.htm
"Television, DVD, Web and computer based photographic content are generally color balanced on professional CRT studio monitors that are electronically adjusted to have a standard Gamma of 2.20, so you’ll get the most accurate images if your display also has this value."
"The Gamma for the Sony CRT agrees perfectly with the 2.20 standard value. (CRT monitors from Ikegami, another major brand of professional studio monitors, also have a Gamma of 2.20 according to their Director of Engineering.)"
andrewfee
Thanks for the reply. I live and learn.
I believe a crt native gamma, depends on which crts you take to be typical and how you measure them. The gamma in the center of the curve or the overall average gamma, the gamma for the green phosphor or the average of all the phosphors, etc. USA says 2.2 or 2.5, and used to say PAL was 2.8 (I have no idea how the got that figure), Europe says 2.35 (and uses a different green phosphor which might have an effect or not, I have no idea) So the native gamma of crt seems to depend on which expert you ask.
tbrunet
Thanks for the reply. So do you use 2.2 as being reference, true to what the colorist saw on the professional CRT studio monitor. Or adjust gamma to suit your viewing conditions. Would you change your gamma for material mastered in Europe to 2.35.
I assume if they are doing a good job the colorist be they in USA or Europe check the image robustness, so the image should look ok at 2.2 to 2.5 gamma.
I am not a purist so go for what I prefer the look of. But have never seen a reference quality display, so do not know what I am missing.
Thanks for the reply. I live and learn.
I believe a crt native gamma, depends on which crts you take to be typical and how you measure them. The gamma in the center of the curve or the overall average gamma, the gamma for the green phosphor or the average of all the phosphors, etc. USA says 2.2 or 2.5, and used to say PAL was 2.8 (I have no idea how the got that figure), Europe says 2.35 (and uses a different green phosphor which might have an effect or not, I have no idea) So the native gamma of crt seems to depend on which expert you ask.
tbrunet
Thanks for the reply. So do you use 2.2 as being reference, true to what the colorist saw on the professional CRT studio monitor. Or adjust gamma to suit your viewing conditions. Would you change your gamma for material mastered in Europe to 2.35.
I assume if they are doing a good job the colorist be they in USA or Europe check the image robustness, so the image should look ok at 2.2 to 2.5 gamma.
I am not a purist so go for what I prefer the look of. But have never seen a reference quality display, so do not know what I am missing.
If I'm reading this correctly, the CRT was set to almost 200cd/m² with black above 0.7cd/m² in that test?
Even if it was 200 and 0.7, that's not even 300:1 contrast!
I can get a flat 2.20 with my old CRT monitor here as well if I don't care what peak white or my black level is.
I believe SMPTE requires monitors to be set to ≈100cd/m² (30fL) and the EBU specifies 80cd/m² for video white (100cd/m² for peak white) with a minimum of 1000:1 CR for grade 1 broadcast monitors.
If I'm reading this correctly, the CRT was set to almost 200cd/m² with black above 0.7cd/m² in that test?
Even if it was 200 and 0.7, that's not even 300:1 contrast!
I can get a flat 2.20 with my old CRT monitor here as well if I don't care what peak white or my black level is.
I believe SMPTE requires monitors to be set to ≈100cd/m² (30fL) and the EBU specifies 80cd/m² for video white (100cd/m² for peak white) with a minimum of 1000:1 CR for grade 1 broadcast monitors.
here's an old thread on Gamma, lots of good info here.
http://www.avsforum.com/avs-vb/showthread.php?t=836259
Nashou
http://www.avsforum.com/avs-vb/showthread.php?t=836259
Nashou
The same paradigm exists for audio. If the industry does not have a "reference" then tweaks made in the production phase will not be reproduced in a predictable manner. Audio EQ or Video tonal emphasis is correlated to the real time feedback the operator is getting from his/her monitors.
Change the reference and the operator makes different adjustments.
For me at home, factory presets and calibration are fine. The manufacturer is using a profile (OETF) that compliments there design. Whether it's 1.9, 2, 2.2, 2.5 ect. is irrelevant..once calibrated the average measured gamma is what it is.
Change the reference and the operator makes different adjustments.
For me at home, factory presets and calibration are fine. The manufacturer is using a profile (OETF) that compliments there design. Whether it's 1.9, 2, 2.2, 2.5 ect. is irrelevant..once calibrated the average measured gamma is what it is.
The .7 cd/m2 was for 10% video level. If you look at part 1 you will see that the measurements for that CRT as setup were 176 cd/m2 for white and .01 cd/m2 for video black (although the .01 would be down at the limits of the lght meter).
Also, from looking at the graph and calculating some things it looks like the gamma was more like 2.3 gamma down low and 2.2 up higher (like above 30% video level).
You are right about that CRT not being setup as they would be for mastering. I ask Dr. Soneira about that in email and he said that each of the monitors was first calibrated for optimum peak luminance and gray-scale at D65. So, it wouldn't have been as setup for mastering because mastering doesn't call for 176 cd/m2. I don't know how setting up the white for mastering would have affected the measurements as far as gamma.
--Darin
The .7 cd/m2 was for 10% video level. If you look at part 1 you will see that the measurements for that CRT as setup were 176 cd/m2 for white and .01 cd/m2 for video black (although the .01 would be down at the limits of the lght meter).
Also, from looking at the graph and calculating some things it looks like the gamma was more like 2.3 gamma down low and 2.2 up higher (like above 30% video level).
You are right about that CRT not being setup as they would be for mastering. I ask Dr. Soneira about that in email and he said that each of the monitors was first calibrated for optimum peak luminance and gray-scale at D65. So, it wouldn't have been as setup for mastering because mastering doesn't call for 176 cd/m2. I don't know how setting up the white for mastering would have affected the measurements as far as gamma.
--Darin
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