Backlight and Contrast(Picture) Setting - AVS Forum
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post #1 of 16 Old 02-24-2012, 12:39 PM - Thread Starter
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I looked through the forum to try to find a general consensus on setting these values, but just want to make sure I am understanding how to set these values. I have two LCD TV's that do not clip whites regardless of the contrast setting. During my recent calibration of these TV's, I decided to leave the backlight setting at 5 (the midpoint) and use the contrast setting to bring the fL of the displays down to 45 fL's (for viewing in a mid-ambiant light room). Looking at the finished results, I am quite happy, but am wondering whether there is a better way.

Have I lost depth of contrast, due to bringing the contrast controls down to 77 on one TV and 85 on the other TV (they were both factory set at 95)?

I now know that lowering the backlight can make the blacks looks better, so should I keep the contrast high and use the backlight to reduce the fL's to my recommended setting.

Again, if my display clipped whites, this would be easier to determine, but since it doesn't I am having problems determining the correct method.
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post #2 of 16 Old 02-24-2012, 12:52 PM
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From everything I have read, set contrast as high as possible without clipping, distortion or discoloration. If you can go to 100% than that is what you set it to. Then use BL to adjust your light output. If the set is still to bright and causing eye strain with BL all the way down, lower the contrast, but that is probably not going to be the case. Also make sure the dynamic contrast/Blacklevel etc are turned off.
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post #3 of 16 Old 02-24-2012, 01:00 PM
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Again, if my display clipped whites, this would be easier to determine

Yeah, one of my LCD's enjoys this problem.

What I found was that I needed to go to the AVS HD709 Color Clipping pattern, and it's there that you can see the problems caused by too high a contrast.

You have to ensure that the three primary colors shown do not clip before digital 235.

I was able to set my contrast to maximum (as you've mentioned), and all looked swell on the contrast pattern, but one of the primary colors was clipping when I examined the Color clipping pattern. I dialed the contrast down until it didn't clip, then I set my BackLight adjustment to my desired luminance with a meter.

Also double check the Color Steps pattern when done your calibration to be sure all six colors aren't clipped.

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post #4 of 16 Old 02-24-2012, 01:36 PM
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Quote:
Originally Posted by bruce View Post

You have to ensure that the three primary colors shown do not clip before digital 235.

You should try to have them not clip at all, all the way to 255.

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post #5 of 16 Old 02-24-2012, 01:39 PM
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Quote:
Originally Posted by rocketlaw View Post

Have I lost depth of contrast, due to bringing the contrast controls down to 77 on one TV and 85 on the other TV (they were both factory set at 95)?

Yes you have, you should maximize contrast, and use backlight to turn down the brightness.

A benefit of using backlight is it will reduce your black level as well so you'll get blacker blacks, you'll maintain your contrast ratio, you'll have more bit depth.

Using the contrast controls lowers contrast ratio and bitdepth.

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post #6 of 16 Old 02-24-2012, 01:45 PM
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Quote:
Originally Posted by sotti View Post

Yes you have, you should maximize contrast, and use backlight to turn down the brightness.

A benefit of using backlight is it will reduce your black level as well so you'll get blacker blacks, you'll maintain your contrast ratio, you'll have more bit depth.

Using the contrast controls lowers contrast ratio and bitdepth.

What do you mean by bit depth? Do you mean smoother gradations and less potential for banding artifacts or is there more to it than that?
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post #7 of 16 Old 02-24-2012, 02:07 PM
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Quote:
Originally Posted by bruce View Post

Yeah, one of my LCD's enjoys this problem.

What I found was that I needed to go to the AVS HD709 Color Clipping pattern, and it's there that you can see the problems caused by too high a contrast.

You have to ensure that the three primary colors shown do not clip before digital 235.

I was able to set my contrast to maximum (as you've mentioned), and all looked swell on the contrast pattern, but one of the primary colors was clipping when I examined the Color clipping pattern. I dialed the contrast down until it didn't clip, then I set my BackLight adjustment to my desired luminance with a meter.

Also double check the Color Steps pattern when done your calibration to be sure all six colors aren't clipped.

bruce

Thanks, that was probably the simplest explanation I have read so far. I also had my contrast set quite high (around 93 on a 42LK450). It seemed ok in white clipping, but in color clipping, it clipped both red and blue. I then dropped it to 86 and no colors clip. Of course, this is a work in progress so it might change again.
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post #8 of 16 Old 02-24-2012, 02:07 PM - Thread Starter
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Thanks guys, makes sense to me.

One other quick question:

I use an HTPC exclusively on all my TV's. Since I use the Intel onboard graphics, there is a bug which prevents me from sending full 0-255 video levels to the display. It defaults to limited 16-235. Since I cannot see the levels BTB and WTW, is the best method to adjust brightness and contrast to make changes until you see the bars start to pull away from level 16 or level 235 and then just stop and change the level back one click.
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post #9 of 16 Old 02-24-2012, 02:19 PM
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Quote:
Originally Posted by colin.p View Post

Thanks, that was probably the simplest explanation I have read so far. I also had my contrast set quite high (around 93 on a 42LK450). It seemed ok in white clipping, but in color clipping, it clipped both red and blue. I then dropped it to 86 and no colors clip. Of course, this is a work in progress so it might change again.

On my LK450, sending component (YCbCr) instead of RGB over the HDMI connection allows me to see no clipping below 235 for red, green, and blue but RGB clips things a bit near 235. It seems the blue channel is the main issue here. I have contrast maxed out at 100/100.
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post #10 of 16 Old 02-24-2012, 02:50 PM
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Since I cannot see the levels BTB and WTW, is the best method to adjust brightness and contrast to make changes until you see the bars start to pull away from level 16 or level 235 and then just stop and change the level back one click.

Yeah, I think that's the best way in that situation.

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post #11 of 16 Old 02-24-2012, 02:55 PM
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Quote:
Originally Posted by rocketlaw View Post

Thanks guys, makes sense to me.

One other quick question:

I use an HTPC exclusively on all my TV's. Since I use the Intel onboard graphics, there is a bug which prevents me from sending full 0-255 video levels to the display. It defaults to limited 16-235. Since I cannot see the levels BTB and WTW, is the best method to adjust brightness and contrast to make changes until you see the bars start to pull away from level 16 or level 235 and then just stop and change the level back one click.

If you are using your computer exclusively, then the computer should still be range 0-255, at least it thinks it is. So have it generate the ramps to 255. If you are using a calibration disc and expanding the levels to 0-255, well then what's encoded on the disc as 235, it becoming 255 on the desktop, so that would work too (and then it's getting put back on the wire as 235).

Just try to maximize the range.

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post #12 of 16 Old 02-24-2012, 02:58 PM
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Quote:
Originally Posted by PlasmaPZ80U View Post

What do you mean by bit depth? Do you mean smoother gradations and less potential for banding artifacts or is there more to it than that?

Correct.

If you are using contrast to make that correction and you have an 8bit LCD panel (it's a bit different with a 10bit panel) lets say you dropped 25% of the luminance, so you are essentially mapping 100% to 80%, so instead of 255, it's more like 200 and instead of 8 bit depth it's closer to 7.5 bits of resolution, because you gave away 50 bits of information to lower the contrast.

This only applies to LCD panels where the actual display device has 8bit steps.

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post #13 of 16 Old 02-24-2012, 03:13 PM
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Originally Posted by sotti View Post


This only applies to LCD panels where the actual display device has 8bit steps.

I believe my LG is a 10-bit panel, though I can't remember where I read that at the moment. Based on what you mentioned about bit depth, is it more critical to maximize it than passing WTW all the way up to 255?
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post #14 of 16 Old 02-24-2012, 03:22 PM
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Quote:
Originally Posted by PlasmaPZ80U View Post

On my LK450, sending component (YCbCr) instead of RGB over the HDMI connection allows me to see no clipping below 235 for red, green, and blue but RGB clips things a bit near 235. It seems the blue channel is the main issue here. I have contrast maxed out at 100/100.

I should have mentioned that I was talking about using the AVSHD 709 mp4 version through my WDTV-Live, and it is set up to use YCbCr, over HDMI. However, using the WOW disk (DVD) following the disk instructions, contrast was at 100 to show just above "ideal white". It still looked ok, but when I lowered the contrast to 94 for the WOW disk, I am now showing all the flashing "stars" above white. No observable change to colors, at least that I can see.

If and whenever I do get a BD player, I will use the AVSHD BD disk to "calibrate" again. I am curious to see how close the two versions are as well as the WOW DVD version. I kind of doubt that I will buy the WOW BD version.
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post #15 of 16 Old 02-24-2012, 03:38 PM
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Quote:
Originally Posted by colin.p View Post

I should have mentioned that I was talking about using the AVSHD 709 mp4 version through my WDTV-Live, and it is set up to use YCbCr, over HDMI. However, using the WOW disk (DVD) following the disk instructions, contrast was at 100 to show just above "ideal white". It still looked ok, but when I lowered the contrast to 94 for the WOW disk, I am now showing all the flashing "stars" above white. No observable change to colors, at least that I can see.

If and whenever I do get a BD player, I will use the AVSHD BD disk to "calibrate" again. I am curious to see how close the two versions are as well as the WOW DVD version. I kind of doubt that I will buy the WOW BD version.

I'm using the PS3 with the AVCHD version (burned to a DVD but plays like a BD) of the AVSHD709 disc.
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post #16 of 16 Old 02-24-2012, 03:38 PM
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Quote:
Originally Posted by PlasmaPZ80U View Post

I believe my LG is a 10-bit panel, though I can't remember where I read that at the moment. Based on what you mentioned about bit depth, is it more critical to maximize it than passing WTW all the way up to 255?

They are part of the same coin.

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