Quantcast ATI MMC gamma settings affect final output? - digitalFAQ Forum
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06-16-2015, 02:22 PM
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Does this screen affect final file output,or only the View settings while capturing?..I Recently noticed this while setting up, Didn't notice it in the "Capture MPEG with ATI Card" Guide.


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06-17-2015, 11:42 AM
sanlyn sanlyn is offline
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Quote:
Originally Posted by rockovids View Post
Does this screen affect final file output
Yes. It's the cap software's proc amp. Most people use it to ensure valid video levels during capture.
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06-18-2015, 05:41 AM
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Whoops! forgot to make Pic visible to viewers! Also not sure about the "GAMMA" setting, seems to affect brightness?, Plus if using AV Toolbox 8710, there are also similar (duplicated) brightness/color,etc..settings on it too,but I tend to leave the Toolbox settings as is/default..(a real pain to access anyway).ATI MMC TV Setup (568x640) (568x640).jpg



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06-18-2015, 07:38 AM
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Quote:
Originally Posted by rockovids View Post
not sure about the "GAMMA" setting, seems to affect brightness?
To give a vastly oversimplified explanation:

Gamma defines the overall brightness of an image, especially in the midtones. Graphically, in the spectrum RGB 0-255, the midle point is ~RGB 128. Raising or lowering gamma raises or lowers the middle range of the spectrum centered at RGB 128, with decreasing effect in the darkest area and decreasing effect in the brightest area.

Think of plotting all the pixel values of an image along a straight line. As a straight line, the brightness of all the pixels is about the same. If you raise gamma, the middle part of the line will curve upward. If you lower gamma, the middle of the line will curve downward. Raise gamma too high, and darks lose density while brights lose detail. Lower it too far, and darker parts will be obscured and the brightest parts will lose perceived brilliance.

Here is a techy article about gamma. Don't worry about the formulas. Just look at the images on the right-hand side. https://en.wikipedia.org/wiki/Gamma_correction. More examples here: http://www.colormatters.com/the-power-of-gamma.

Monitors also have gamma settings. An uncalibrated monitor out of the box almost always has gamma that is off-spec from the ideal, either too low or too high. Working in video or graphics with an uncorrected gamma will skew the results of the way your monitor displays an image. One effect of low gamma is colors that appear oversaturated. If too high, colors appear unsaturated (washed out). Making corrections with an uncalibrated monitor will affect the way your images display on other monitors.

Gamma is also affected somewhat by brightness and contrast controls. Brightness raises or lowers dark values. Contrast raises or lowers bright values. Each of the controls is less effective at the middle of the spectrum than at the dark or bright end, but both affect the midpoint to some extent.

Another oversimplified item: In RGB, the gamma of each color can be adjusted independently or all at the same time. In YUV, gamma affects only luma, which ultimately affects all colors at the same time. There is no independent gamma control for chroma in YUV.

There are some limited but basic LCD panel test charts at this website: http://www.lagom.nl/lcd-test/. But the best way to correctly adjust a monitor is with a monitor calibration kit such as those from X-Rite or Spyder. Doing it with test patterns is iffy and difficult. Doing it by eye is impossible.
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06-19-2015, 11:48 AM
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Thanks Sanlyn, Helps me understand this one of many complicated video subjects!..And you reminded me that I still need to calibrate these 2 Viewsonic monitors I recently purchased specifically for video work!..(Right now for personal use/capture of my own tapes..maybe for others later?).. I hope there is a way I calibrate them that will work on both my XP Capture PC (both monitors), and also my Win7 Video/Edit PC (one monitor)..but usually won't be using both PC's at same time...Right now funds are non-existent for the Xrite or Spyder...Hope I can use the lagom site for now...complete accuracy (for now) isn't as important to me, as at least knowing they are calibrated better than "out of the box"...Also I think there is/was a calibration cd file(s) available in premium Forum.
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06-20-2015, 07:30 AM
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The answer is complicated.

sanlyn probably hasn't seen what I have. His definitions of gamma is fine, though very simplified.

The "video properties" will always work. I've never seen them fail.

But the gamma settings sometimes are not recorded, and affects viewing only. However, it's supposed to affect the video recording as well. I've never found any logic behind it. All I know if that different cards, different drivers, and different versions of ATI MMC behave differently. I can usually "fix" it by uninstalling everything ATI, and trying again with different packages. Only once have I been completely unable to fix it. (And yet, when that card was installed in a new system, it worked fine again. WTF?!)

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06-20-2015, 12:52 PM
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So I can test on my system by setting gamma too high or low, so it looks terrible, then see if that transfers to captured file.
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