Can CUT and DRV settings have an effect on gamma? I've scoured the board using search and have read mixed messages.

I read kal's Dummies guide and it says that adjusting cut and drive across the board is the same as adjusting brightness and contrast. However, somewhere else on the forum someone said you could effectively change gamma that way.

I'd basically agree with what Kal said, though certainly you'd want to check and perhaps tweak gamma afterwards. Gamma will have a much more significant effect on cut/drive settings(per priimary) or brightness/contrast (global) than the other way around. Still, there is some interaction there and obvioulsy a wrongly set brightness/contrast control will yield you variation in the effective gamma, particularly if brightness is set too high, or contrast significantly too low, youll end up with a lower effective gamma.

But if you are attempting to affect changes to the gamma response, using cuts/drives or the brightness/contrast controls is going to be pretty futile since it won't really affect that unless you set them grossly incorrectly. There's really only one correct position for those controls, so...

I read kal's Dummies guide and it says that adjusting cut and drive across the board is the same as adjusting brightness and contrast. However, somewhere else on the forum someone said you could effectively change gamma that way.

tsanga,

In my experience, moving contrast and brightness will affect gamma to a certain extent. The Gamma graph can be thought of simply as the brightness response between 0% and 100% amplitude. So, when you change brightness/black level, it alters the lower end brightness response mostly (how much it also affects the higher end depends on the display) so this will have an affect on your gamma curve especially at the low end. Typically when your lower brightness, you'll see gamma increase at the low end - in some sense, the entire response shifts right to left with a greater shift the closer you get to 0%. As for the Contrast control, it's pretty much the same thing with things shifting left to right as you increase the control and vice versa if you lower it. So, this will usually have the effect of raising gamma at the high end if your gamma is sloping downward (e.g. 2.1 at 85% but 1.8 at 95%). In addition to the gamma graph changing, moving your brightness/contrast will also affect your grayscale response. On my Samsung LCD set, I can see this affect perfectly as I lower/raise the Contrast control. I have a blue bump at 60% with Contrast at 85 or so. If I leave everything else alone and bump the control up to 98, the blue bump moves to 50% and changes shape slightly.

With all that said, I would agree with Chris that you don't want to alter your Brightness control in an attempt to move your gamma curve. You want to set Brightness using a black bars test pattern. Of course, with that said, if you understand how things work and are willing to sacrifice shadow details at the lowest end (1%) because you want a better brightness response at say 5% - 30% then it is a compromise you have to make - but it is important to know what the compromise is and what you're sacrificing. As for Contrast, since setting Contrast can be a bit more subjective (assuming that you're not clipping whites or causing color shifts at the high end of the grayscale), it may be preferable to lower it a bit if that gives a decent improvement to the gamma response. You will sacrifice some on/off contrast in exchange for a more natural looking contrast across most of the range.

I also would not try and influence gamma by using your cut/drive/grayscale controls - I would only change those in order to get the right RGB mix in order to get as close to D65 as you can.

hope this helps,


--tom

Thanks, guys. That's the way I thought it worked, but this post (http://www.avsforum.com/avs-vb/showthread.php?p=13406360#post13406360) confused me briefly.

Thanks, guys. That's the way I thought it worked, but this post (http://www.avsforum.com/avs-vb/showthread.php?p=13406360#post13406360) confused me briefly.

tsanga,

The all cuts/all drives settings on some displays are probably going to act very similar to adjusting the brightness and contrast controls. It really depends on how things are implemented/engineered for that particular display. My feeling after reading a lot of stuff here and calibrating my own displays is that it's best not to tinker too much with the individual RGB grayscale controls in order to alter gamma - mainly because you'll throw off your D65 tracking across the scale in exchange for perhaps a slight improvement in gamma. This may also be true for the all cuts/gains controls. If your set has these, it would probably be best to just experiment. Leave everything else the same and change the all cuts and re-measure. See what changed - did the grayscale response change, what happened to gamma and black level, etc.? Once you know how it behaves you can then make a decision if the control is useful or not for your calibration needs.

hope this helps,


--tom

Yeah, I actually don't know what Mr.D means by that.