Display calibration

splatterpop · 2008-04-20, 14:03

Hi all,

I would like to share the experiences that i had while setting up my video configuration . I often felt that the image quality was not like I thought it could be, giving me a dull image impression. After I did the procedure which is described here, I ended up with a very crisp, cinema-like picture and a smile on my face, which I would like to share with you.

The general setup
I use a Samsung 400DX monitor, connected to a ATI RS600 based computer (ASRock 4core 1333 fullhd), either via DVI-to-DVI or DVI-to-HDMI. Also, the latest ATI catalyst drivers are installed, with CCC running in the background. A Toshiba 32WL58 TV set was used in previous setups, some of the results refer to this type of monitor.

Calibration goals
Here's what I wanted to achieve.
+ black should be as black as possible.
+ white should be as bright as possible.
+ grey values should be maintained as closely as possible, especially at very low and very high brightness levels.
+ color calibration will not be covered here.
+ Only freely available resources should be used, so everybody can perform and validate the same steps at no cost, improve and give feedback.

Connection considerations
In my experience, a great difrerence is made by the way the monitor is connected to the computer.

Right away, a HDMI connection seemed to deliver a very contrasted, maybe over-contrasted picture with lots of black in it, while DVI delivered less contrast and color. Also, the two offered different sets of image controls on the monitor. For example, the HDMI input offers a color saturation control, while DVI does not. That might depend on the monitor too.

Also, HDMI never let me use the native panel resolution. I always needed to tweak the image. I am not into HDMI enough as to point out a reason for this, but it occured to me on both monitors. The 400DX's native resolution of 1366x768 is available only when using DVI. The 32WL58's native resulution, which is supposed to be 1366x768, did not give a good enough picture, I had to settle for 720p. In both cases, the image edges were cut off for some reason, so the desktop had to be resized to fit the panel, further reducing image resolution. I ended up with somthing like 1088x684 for the 32WL58 and 1824x1016 for the 400DX.

As you see, despite all the drawbacks, I settled for HDMI in both cases. The 32WL58 alternatively only offers analog VGA, giving an image quality that was unimpressive. The 400DX does offer DVI, but lacks the capability for black point adjustment - both brightness and contrast controls seem to modify the white point. I don't know wheter this is a bug or not, but that ruled out DVI instantly on that device, although I could have gotten the native resolution without undersampling.

Monitor calibration
So now lets get into the procedure. The ambient light should be low during screen adjustment. We will be going through the signal chain from back to front, starting with the monitor. These three controls will be needed:

+ black point (brightness control)
+ white point (contrast control)
+ gamma adjustment (adjustment of grey tones)

Some monitors offer a gamma control, mine doesn't. So I used ATI's gamma adjustment in CCC.

First, let's adjust the black point. To me, this is a most important value, as it highly determines the perceived image contrast. Set your Windows desktop to solid black and hide the task bar, then use the brightness control on your monitor to find the threshold where the image starts to turn dark grey (45 out of 100 on the 400DX). Set a value just below the threshold, and try to keep the image as "black" as possible. Watch the screen from a close distance while you do this.

Next, adjust the white point. Most LCDs do this by setting the backlight intensity, so set this value as high as possible. The 400DX can be very bright, so I used 70 out of 100.

Finally, adjust the grays by setting the gamma value. This is a highly subjective task, some people may prefer higher contrasts than others. Also, in CCC there are different settings for "desktop", which applies for windowed display, and "3d", which applies for fullscreen video and VMR9 exclusive mode. Be sure to set the two equally.

I found this resource to be helpful:

via Testprint

Here you will find all sorts of test prints. First, use "Einser" and display it full screen.

+ Use the desktop gamma control to make as many of the white-on-black numbers appear as possible. Don't go too high, say above 1.6, or the image display might become unnatural. I found 1.4 to be best, but that might differ. Watch the screen from a close distance while you do this, or the black-on-white numbers might overshine the very dim white-on-blacks. At least the number "3" should become barely visible. As a last resort, you might consider increasing the black point by a few notches. When you are done, set the 3d gamma value to the same value.

+ Only if necessary, adjust the white point again so that as many of the black-on-white numbers become visible. A "2" is good, a "1" is perfect.

+ See whether you get a natural looking image display by checking the "Testprint" image. Readjust the gamma if necessary.

Keep in mind, the results depend highly on the quality of your display. In the best case, the white point will not need any adjustment.

Decoder adjustment
At this point, you have set up your monitor to display the RGB desktop color space correctly. Still, if you watch a video or TV, you see black appear as gray. Why is that?

The RGB values, ranging from 0 to 255 for each color, start off at a value of 16, ranging up to 235, which seems to be an industry standard. So in RGB color space, the representation of black should be (0,0,0), but it actually is delivered as (16,16,16), which means dark gray in our own color space. The way around this is to transform the video color space into our now calibrated RGB desktop color space.

+ NVIDIA Forceware / MPV decoder (TV, DVD)
++ adjust the brightness to about minus 16 notches.
++ adjust the contrast to about 16 notches plus.
++ best check with a letterboxed TV program. The black image portions should appear jet black.

+ ffdshow (Video)
++ activate the "levels" control. Set the lower threshold to 15 and use "full range".
++ consider lowering the upper ("white") threshold to 236.
++ activate the histogram function to validate the settings.

Cheers,
splatterpop

BobMysterios · 2008-04-22, 05:14

Thanks for the testpic, using it and the realization that my saturation was way too high, and I finally have the picture quality I've been looking for.

Thanks a lot.

pbb · 2008-08-07, 17:52

Regarding adjusting the levels using ffdshow; isn't it better to use the UseBT601CSC registry hack? Or did you not know about this?

splatterpop · 2008-08-07, 18:40

No, I did not. Thanks, I will check it out. I believe it is ATI specific?

I did some digging and found some related links. Very interesting because the posterization problem is discussed too. I am curious to know if the tweaks will work on my X1250...

AVS Forum - View Single Post - ATI Radeon HD 2X00 (2400,2600,2900) series owners thread
AVS Forum - View Single Post - ATI Radeon HD 2X00 (2400,2600,2900) series owners thread

Thanks again dude, great hint.

pbb · 2008-08-07, 18:52

Yes, ATI specific. I don't know the details, and haven't tried it out myself yet, but this should output video < 720px with 0..255 range. (720px and higher already outputs in 0..255 range. I believe it's called BT601 and BT607 colorspaces.)

Also, using ffdshow disabled HW acceleration, though that does not seem to be a problem when only playing SD content. (Like SD TV signals and DVDs.)

Haven't tried much yet, I first wanted to check out if anybody knows of downsides to applying that registry hack...

damaster · 2008-09-11, 13:10

For all those playing high definition content, you should definitely grab a copy of Digital Video Essentials: HD Basics and calibrate your TV/monitor using the test patterns and instructions on that disc. It is available in both BluRay and HD-DVD formats.

If you don't have an HD-DVD or BluRay drive, then you can always grab the AVS calibration disc files (mount the ISO image) from AVS HD 709 - Blu-ray & HD DVD Calibration Disks - AVS Forum.

If you're using an ATI card outputting to a TV that expects video levels (16-235), then you should make the following changes to your set up:
- Make sure you have the UseBT601CSC registry hack for SD content. See ATI HD Registry Tweaks for more details.
- Set your brightness/contrast in ATI Catalyst Control Center -> Color (not the one under Avivo Video settings) to +31/73 respectively. This will output everything at 16-235 levels instead of 0-255. Under the Avivo Video settings -> Basic make sure the "Use application settings" checkbox is enabled.
- If you're using PowerDVD Ultra for BluRays or HD-DVDs, then the brightness/contrast settings in Catalyst Control Center don't have an effect and PowerDVD Ultra will still output HD content at 0-255 PC levels. To get PowerDVD Ultra to output HD content at 16-235 (video levels) you actually have to adjust the brightness/contrast in PowerDVD itself. While playing a BluRay or HD-DVD, right-click and select Configuration, and then go to the Video tab, hit Advanced, and go to the Color tab and set brightness to +19 and contrast to -5. Now if you calibrate using the DVE: HD Basics or the AVS disc in PowerDVD Ultra, your display's brightness/contrast settings will be consistent across all videos you play (even the ones in MediaPortal).

And if you want to get really adventurous, then buy yourself an EyeOne Colorimeter and calibrate like a pro, including adjusting your grayscale. See here for more details on that: GREYSCALE & COLOUR CALIBRATION FOR DUMMIES

My recommendation is NOT to use ffdshow since it completely disables hardware acceleration. My recommendation is to use MPC Video Decoder to leverage hardware acceleration and get the best possible picture quality. See my post here for more details on that: A decoder for the new track could not be found. track type: SRT/UTF8

pbb · 2008-09-12, 13:18

Thanks for the guides, splatterpop and damaster! I've started putting this stuff in the wiki: GeneralUserGuides/DisplayCalibration - MediaPortal Wiki Documentation

splatterpop · 2008-09-12, 20:43

I'd like to add a couple of things:

I noticed great picture improvements for DVD and TV when i switched to the ffdshow raw video decoder. I didn't dig into this much further, and maybe somebody could comment on this in greater detail. But it seems to me that by doing this, ffdshow does not try to decode the video stream, instead the MPEG2 decoder is invoked. Still all of ffdshow's filters stay active and you get the same color space transformation.

Somehow a color space transformation seems to be built into HDMI (which does make sense in a way). I noticed that when switching from a DVI to a HDMI connection, the image becomes considerably darker and more contrasty, which means that the black and white points differ. This makes sense as long you use video sources together with HDMI which use the output level range from 16 to 236. Yet this makes no sense for desktop applications like picture viewers, browsers etc. In my opinion, in a media center setting each source must be calibrated to the desktop color space.

2008-04-20, 14:03	#1 (permalink)
splatterpop Portal Member Join Date: Dec 2007 Posts: 50 Thanks: 1 Thanked 2 Times in 2 Posts Country: My System	Display calibration Hi all, I would like to share the experiences that i had while setting up my video configuration . I often felt that the image quality was not like I thought it could be, giving me a dull image impression. After I did the procedure which is described here, I ended up with a very crisp, cinema-like picture and a smile on my face, which I would like to share with you. The general setup I use a Samsung 400DX monitor, connected to a ATI RS600 based computer (ASRock 4core 1333 fullhd), either via DVI-to-DVI or DVI-to-HDMI. Also, the latest ATI catalyst drivers are installed, with CCC running in the background. A Toshiba 32WL58 TV set was used in previous setups, some of the results refer to this type of monitor. Calibration goals Here's what I wanted to achieve. + black should be as black as possible. + white should be as bright as possible. + grey values should be maintained as closely as possible, especially at very low and very high brightness levels. + color calibration will not be covered here. + Only freely available resources should be used, so everybody can perform and validate the same steps at no cost, improve and give feedback. Connection considerations In my experience, a great difrerence is made by the way the monitor is connected to the computer. Right away, a HDMI connection seemed to deliver a very contrasted, maybe over-contrasted picture with lots of black in it, while DVI delivered less contrast and color. Also, the two offered different sets of image controls on the monitor. For example, the HDMI input offers a color saturation control, while DVI does not. That might depend on the monitor too. Also, HDMI never let me use the native panel resolution. I always needed to tweak the image. I am not into HDMI enough as to point out a reason for this, but it occured to me on both monitors. The 400DX's native resolution of 1366x768 is available only when using DVI. The 32WL58's native resulution, which is supposed to be 1366x768, did not give a good enough picture, I had to settle for 720p. In both cases, the image edges were cut off for some reason, so the desktop had to be resized to fit the panel, further reducing image resolution. I ended up with somthing like 1088x684 for the 32WL58 and 1824x1016 for the 400DX. As you see, despite all the drawbacks, I settled for HDMI in both cases. The 32WL58 alternatively only offers analog VGA, giving an image quality that was unimpressive. The 400DX does offer DVI, but lacks the capability for black point adjustment - both brightness and contrast controls seem to modify the white point. I don't know wheter this is a bug or not, but that ruled out DVI instantly on that device, although I could have gotten the native resolution without undersampling. Monitor calibration So now lets get into the procedure. The ambient light should be low during screen adjustment. We will be going through the signal chain from back to front, starting with the monitor. These three controls will be needed: + black point (brightness control) + white point (contrast control) + gamma adjustment (adjustment of grey tones) Some monitors offer a gamma control, mine doesn't. So I used ATI's gamma adjustment in CCC. First, let's adjust the black point. To me, this is a most important value, as it highly determines the perceived image contrast. Set your Windows desktop to solid black and hide the task bar, then use the brightness control on your monitor to find the threshold where the image starts to turn dark grey (45 out of 100 on the 400DX). Set a value just below the threshold, and try to keep the image as "black" as possible. Watch the screen from a close distance while you do this. Next, adjust the white point. Most LCDs do this by setting the backlight intensity, so set this value as high as possible. The 400DX can be very bright, so I used 70 out of 100. Finally, adjust the grays by setting the gamma value. This is a highly subjective task, some people may prefer higher contrasts than others. Also, in CCC there are different settings for "desktop", which applies for windowed display, and "3d", which applies for fullscreen video and VMR9 exclusive mode. Be sure to set the two equally. I found this resource to be helpful: via Testprint Here you will find all sorts of test prints. First, use "Einser" and display it full screen. + Use the desktop gamma control to make as many of the white-on-black numbers appear as possible. Don't go too high, say above 1.6, or the image display might become unnatural. I found 1.4 to be best, but that might differ. Watch the screen from a close distance while you do this, or the black-on-white numbers might overshine the very dim white-on-blacks. At least the number "3" should become barely visible. As a last resort, you might consider increasing the black point by a few notches. When you are done, set the 3d gamma value to the same value. + Only if necessary, adjust the white point again so that as many of the black-on-white numbers become visible. A "2" is good, a "1" is perfect. + See whether you get a natural looking image display by checking the "Testprint" image. Readjust the gamma if necessary. Keep in mind, the results depend highly on the quality of your display. In the best case, the white point will not need any adjustment. Decoder adjustment At this point, you have set up your monitor to display the RGB desktop color space correctly. Still, if you watch a video or TV, you see black appear as gray. Why is that? The RGB values, ranging from 0 to 255 for each color, start off at a value of 16, ranging up to 235, which seems to be an industry standard. So in RGB color space, the representation of black should be (0,0,0), but it actually is delivered as (16,16,16), which means dark gray in our own color space. The way around this is to transform the video color space into our now calibrated RGB desktop color space. + NVIDIA Forceware / MPV decoder (TV, DVD) ++ adjust the brightness to about minus 16 notches. ++ adjust the contrast to about 16 notches plus. ++ best check with a letterboxed TV program. The black image portions should appear jet black. + ffdshow (Video) ++ activate the "levels" control. Set the lower threshold to 15 and use "full range". ++ consider lowering the upper ("white") threshold to 236. ++ activate the histogram function to validate the settings. Cheers, splatterpop

2008-08-07, 18:40	#4 (permalink)
splatterpop Portal Member Join Date: Dec 2007 Posts: 50 Thanks: 1 Thanked 2 Times in 2 Posts Country: My System	No, I did not. Thanks, I will check it out. I believe it is ATI specific? I did some digging and found some related links. Very interesting because the posterization problem is discussed too. I am curious to know if the tweaks will work on my X1250... AVS Forum - View Single Post - ATI Radeon HD 2X00 (2400,2600,2900) series owners thread AVS Forum - View Single Post - ATI Radeon HD 2X00 (2400,2600,2900) series owners thread Thanks again dude, great hint. Last edited by splatterpop; 2008-08-07 at 18:50. Reason: Automerged Doublepost

2008-09-11, 13:10	#6 (permalink)
damaster Portal Member Join Date: Nov 2007 Posts: 169 Thanks: 2 Thanked 8 Times in 7 Posts Country: My System	For all those playing high definition content, you should definitely grab a copy of Digital Video Essentials: HD Basics and calibrate your TV/monitor using the test patterns and instructions on that disc. It is available in both BluRay and HD-DVD formats. If you don't have an HD-DVD or BluRay drive, then you can always grab the AVS calibration disc files (mount the ISO image) from AVS HD 709 - Blu-ray & HD DVD Calibration Disks - AVS Forum. If you're using an ATI card outputting to a TV that expects video levels (16-235), then you should make the following changes to your set up: - Make sure you have the UseBT601CSC registry hack for SD content. See ATI HD Registry Tweaks for more details. - Set your brightness/contrast in ATI Catalyst Control Center -> Color (not the one under Avivo Video settings) to +31/73 respectively. This will output everything at 16-235 levels instead of 0-255. Under the Avivo Video settings -> Basic make sure the "Use application settings" checkbox is enabled. - If you're using PowerDVD Ultra for BluRays or HD-DVDs, then the brightness/contrast settings in Catalyst Control Center don't have an effect and PowerDVD Ultra will still output HD content at 0-255 PC levels. To get PowerDVD Ultra to output HD content at 16-235 (video levels) you actually have to adjust the brightness/contrast in PowerDVD itself. While playing a BluRay or HD-DVD, right-click and select Configuration, and then go to the Video tab, hit Advanced, and go to the Color tab and set brightness to +19 and contrast to -5. Now if you calibrate using the DVE: HD Basics or the AVS disc in PowerDVD Ultra, your display's brightness/contrast settings will be consistent across all videos you play (even the ones in MediaPortal). And if you want to get really adventurous, then buy yourself an EyeOne Colorimeter and calibrate like a pro, including adjusting your grayscale. See here for more details on that: GREYSCALE & COLOUR CALIBRATION FOR DUMMIES My recommendation is NOT to use ffdshow since it completely disables hardware acceleration. My recommendation is to use MPC Video Decoder to leverage hardware acceleration and get the best possible picture quality. See my post here for more details on that: A decoder for the new track could not be found. track type: SRT/UTF8 Last edited by damaster; 2008-09-11 at 13:13.

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2008-04-22, 05:14	#2 (permalink)
BobMysterios Portal Member Join Date: Dec 2007 Posts: 34 Thanks: 0 Thanked 2 Times in 2 Posts	Thanks for the testpic, using it and the realization that my saturation was way too high, and I finally have the picture quality I've been looking for. Thanks a lot.

2008-08-07, 17:52	#3 (permalink)
pbb Docs Team Join Date: Oct 2006 Location: Trondheim Age: 36 Posts: 297 Thanks: 5 Thanked 20 Times in 9 Posts Country: My System	Regarding adjusting the levels using ffdshow; isn't it better to use the UseBT601CSC registry hack? Or did you not know about this?

2008-08-07, 18:52	#5 (permalink)
pbb Docs Team Join Date: Oct 2006 Location: Trondheim Age: 36 Posts: 297 Thanks: 5 Thanked 20 Times in 9 Posts Country: My System	Yes, ATI specific. I don't know the details, and haven't tried it out myself yet, but this should output video < 720px with 0..255 range. (720px and higher already outputs in 0..255 range. I believe it's called BT601 and BT607 colorspaces.) Also, using ffdshow disabled HW acceleration, though that does not seem to be a problem when only playing SD content. (Like SD TV signals and DVDs.) Haven't tried much yet, I first wanted to check out if anybody knows of downsides to applying that registry hack...

2008-09-12, 13:18	#7 (permalink)
pbb Docs Team Join Date: Oct 2006 Location: Trondheim Age: 36 Posts: 297 Thanks: 5 Thanked 20 Times in 9 Posts Country: My System	Thanks for the guides, splatterpop and damaster! I've started putting this stuff in the wiki: GeneralUserGuides/DisplayCalibration - MediaPortal Wiki Documentation

2008-09-12, 20:43	#8 (permalink)
splatterpop Portal Member Join Date: Dec 2007 Posts: 50 Thanks: 1 Thanked 2 Times in 2 Posts Country: My System	I'd like to add a couple of things: I noticed great picture improvements for DVD and TV when i switched to the ffdshow raw video decoder. I didn't dig into this much further, and maybe somebody could comment on this in greater detail. But it seems to me that by doing this, ffdshow does not try to decode the video stream, instead the MPEG2 decoder is invoked. Still all of ffdshow's filters stay active and you get the same color space transformation. Somehow a color space transformation seems to be built into HDMI (which does make sense in a way). I noticed that when switching from a DVI to a HDMI connection, the image becomes considerably darker and more contrasty, which means that the black and white points differ. This makes sense as long you use video sources together with HDMI which use the output level range from 16 to 236. Yet this makes no sense for desktop applications like picture viewers, browsers etc. In my opinion, in a media center setting each source must be calibrated to the desktop color space.