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| How-to: Better blacks on your LCD http://www.wsgf.org/phpBB3/viewtopic.php?f=63&t=13789 |
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| Author: | Ryom [ 21 Oct 2006, 10:28 ] |
| Post subject: | How-to: Better blacks on your LCD |
95% or better of all widescreen monitors people are using on this forum are LCD's. Many use their monitors for watching movies as well as playing games. A notable shortcoming of LCD's is their difficulty in producing a true black. Oftentimes a significant amount of light bleeds through the panel, when this occurs you get black clipping as the lower tones are obscured by the light leakage. Black clipping doesn't necessarily look bad, and it may even be aesthetically pleasing to some (and it helps hide compression artifacts). However, you WILL LOSE detail in the blacks, and depending on how much light is leaking past your panel, you could be losing much more of your shadow detail then you realize. Place your panel in a pitch black room, set it to display an RGB 0,0,0 color at fullscreen (nothing but black displayed anywhere on the screen) Let your eyes adjust and take note of how much light the panel casting off. If you can see significant illumination then you are probably clipping blacks. My Westinghouse LVM-37w3 37" monitor is a particularly poor performer with regards to black levels and the amount of light generated when displaying black in a dark room is sadly impressive. I noticed that I was having difficulty discerning details in certain media I play... Batman Begins was entirely TOO dark, the menu screen of KOTOR2 where the black robed figures stands amidst shadowy fog was turned into a mass of blackness. You must create a custom gamma curve to account for this behavior of LCDs if details are important to you. To do this properly you should figure out how much light is leaking past your panel. To find out what settings I should use I did this: I taped a 4x6 matte black sheet of paper onto the bezel of my monitor so it stuck off the side (and wouldn't be illuminated by the panel) and I got my camera out (disable your flash!) and dimmed the room and took a shot, where the image was exposed so that the black paper was just above full black... RGB 5,5,5 roughly. I brought this into photoshop and selected only the black paper, and used the average filter to sample all the values in the selection and create a single average value. I selected the curves tool and reduced the black point until the paper was RGB 0,0,0. I then selected just the screen itself, averaged it to find out what it was creating black as, and read the RGB values in the information panel (they were 26,26,26.) This means that any values sent to the display under RGB 26,26,26 would begin to wash out and become fully clipped eventually as the values decreased. With this knowledge we can account for this with a custom gamma curve in our video driver control panel. Now, the Gamma curve is by default set thusly: Black is 0.00, Mid-Grey is 0.50, and Full White is 1.00 which creates a straight line. We must raise the black point so that RGB 0,0,0 is sent to the display at RGB 26,26,26. We divide the curves max value of 1 by the 256 levels of gray we have with RGB to give us a value of 0.00390625 and we multiply this by our RGB value of 26 to give us the corresponding curves value... 0.1015625 which is what we need to set out black point gamma to (I rounded it to .1) To edit the gamma curve in the latest nvidia drivers do this: Right click on your desktop and select properties, go to the settings tab of the display properties box, then then click the advanced button in the lower right. Select the Tab that has your GFX card model listed on it (the one with the nvidia logo) and in the flyout list select Color Correction. You will know see a diagonal line bisecting a 10x10 grid. This is your gamma curve, to edit it you need to select Advanced Mode from the Color Profile drop down list directly below the grid. This allow you to edit (and add or remove) points on the grid. Click on the middle point, and drag it off the screen, this will remove it so that our curve doesn't curve when we alter the black point... we want it to stay straight. Then click the lowest point in the bottom left, this is your black point. To the immediate right of the grid are two text boxes marked In and Out. In should be 0.00, and you will edit Out to be 0.10 which will raise the black point to RGB 26,26,26. Hit the Save As... button and name your profile something you'll remember (Monitor name Calibration for example: Westy LVM-37w3 Calibration) and then hit apply. Your black point should now be set appropriately. Open up a small (only covering a small part of your monitor, doesn't need to be fullscreen) grayscale ramp on your display (a gradient that goes from RGB 0 to RGB 255) and then get into your monitors brightness, contrast, and backlight settings. Reduce the backlight to a comfortable viewing level. Raising contrast will lower your white point (the higher the value, the more whites will be clipped), lowering the brightness setting with raise your black point (the lower the values, the more black will be clipped) Raise the contrast until your whites are clipping (the white eats up more of the ramp) then lower it until you see a smooth transition from gray to pure white. Then lower your brightness until black starts clipping (the black eats up more of the ramp) and then raise it until you have a smooth transition from gray to deep black. Your display is now reasonably calibrated to display its maximum contrast. Find a scene in a video or picture that has lots of shadow detail and pause it, and then in your control panel select between the standard curve and the calibrated curve you saved in the drop down. If your panel had mediocre black levels, you should see the shadow details much more clearly now. If you don't you messed up somewhere or your display has very good black levels already :) Please also be aware that any compression artifacts in your compressed media that were hidden/clipped before will becomes much more visible when your display is calibrated and has a high baseline luminance (poor black levels). This new setting will probably look a bit dingy for gaming and such because this will have reduced contrast a bit, so you'll probably want to create a second curve that boosts the contrast and have it assigned to your custom game profiles (also in your driver panel) See the attached screenshots for reference. Alternately, if your panel has a gaming mode button, you can simply set new values that increase contrast for gaming and toggle it when needed. Click the link for a screenshot of the nvidia gamma controls. The important bits are highlighted in green. Click the link for a screenshot of the nvidia application specific profile controls. The important bits are highlighted in green. Click the link for a screenshot of my desktop while I was calibrating Note that the screenshot may look a bit off for you because it has been specifically calibrated for my display. This section added 6/28/07: (ALL CAPS words or phrases in this post are for areas of special emphasis, not yelling. The bolded lines are the ones that directly answer the previous poster's question) The position of the BLACK REFERENCE OBJECT (matte black construction paper in my case) doesn't matter, just so long as both the matte black object and the screen are in the photo. The purpose of taking a picture at an exposure where the paper IS NOT captured at RGB 0,0,0 is so that we know where our unclipped black point will be by defining it in our image editor. If you try to capture the black reference object at RGB 0,0,0 how do you know that you aren't clipping blacks thereby giving you a false reading? In order to do that, you'll have to raise or lower the exposure time on your camera by using the MANUAL shooting mode. Set your F-Stop/Aperture to the maximum wide open setting (the lowest number available) and then adjust exposure time until you get the black reference object above RGB 0,0,0. This is trial and error unless you have a light meter. The picture HAS to be taken in as much darkness as possible so that we can remove ambient light reflection on the panel from the equation, because that can also cause false readings. If you have no idea what I've just said, you'll probably need to check your camera manual and read a few photography tutorials online, or consult a friend familiar with photography basics. The reason for all this fooling around is so that we can bring that photo into our image editor (I'll use photoshop for my example, but the GIMP or paint.net or paint shop pro will all work just fine) and adjust the LEVELS, CURVES, or BRIGHTNESS/CONTRAST of the picture until the averaged reading of the black reference object is 0,0,0. To get an averaged reading, either use the sampling tool set to 5x5 sampling or select just the black reference object with the selection tools and then BLUR->AVERAGE or BLUR->GAUSSIAN to a large amount and then take a reading with the sampling tool. Once we have our black point set, we then take an averaged reading of the screen in the same manner as above. The sampled value is the amount of light leaking through evenly the entire panel (BACKLIGHT BLEED) that causes the entire panel to be slightly illuminated when what we ideally want (but can't have due to current technological limitations of LCDs) is absolutely no illumination at all. In the measurement for my Westinghouse LVM-37w3, I found that the minimum panel luminance was 10% (RGB 25,25,25), and IF the panel manufacturer DID NOT ACCOUNT FOR THIS bleed with a built in compensation curve (or overcompensated with the internal curve thereby causing black crush which can be compensated for by moving the black point in our video display options in the opposite direction that we would move it for uncompensated blacks), then that means our lowest black values will be WASHED OUT by the BACKLIGHT BLEED making our deepest black tones muddy and lacking in contrast. To get around this, we plug our minimum panel luminance number into a custom output curve for our video display card. Basically, this means that we are remapping black to start at RGB 25,25,25 (or whatever your measurement was) instead of RGB 0,0,0 so that the black tones are represented properly by our panel. This sacrifices overall contrast to improve the contrast of the blacks (a notorious weak point of LCDs) and grayscale tracking. Sacrificing a bit of our overall contrast is not as bad as it sounds. The blacks benefit FAR more than the hit to our overall contrast would suggest, because overall contrast in most current LCDs is FANTASTIC, but the BLACK PERFORMANCE is not usually so great. The side effect of this adjustment is that it improves overall gray tracking which should make your media look much better overall. If you find yourself CONSTANTLY adjusting the brightness and color to get DVD rips or games to look just right, poor gray tracking is probably to blame. Once your panel is properly set, the only reason you should be forced into adjusting it is for media that isn't affected by the compensation curve (some overlayed video acceleration) or for media that is actually not color corrected properly (this is rare). Black crush improves overall contrast but sacrifices black contrast and causes inaccurate gray tracking as a side effect, unless the manufacturer compensated for THAT side effect by creating another point on the adjustment curve, with the possible and likely side effect of THAT being false contouring. |
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| Author: | skipclarke [ 21 Oct 2006, 14:38 ] |
| Post subject: | How-to: Better blacks on your LCD |
"Many use their monitors for watching movies as well as playing games." The most ingnored facts when one is setting up an LCD, are as follows: For all PC Monitors also being used for TV or movie viewing & for all TV's used as PC Monitors You cannot setup the screen to be perfect for both. As the coding values of the information used to display games & movies - is different... Even for the values for RGB display, as well as for other levels. NOTE: Console games are coded using the values for TVs not for PC Monitors. Read the why & how-for here: Tutorial: Viewing Image Quality-PC Monitor/TV/Consoles/DVD The best you can hope to get is with the Dual Function LCD's such as the Viewsonics (& other brands) that also produce specific .ini & .icm drivers for their unit. These units are produced with the intention of them being used for Dual use - both PC & DVD. |
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| Author: | Ryom [ 22 Oct 2006, 00:54 ] |
| Post subject: | How-to: Better blacks on your LCD |
I'm not sure of the point you are attempting to add to my post doug, could you clarify? |
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| Author: | skipclarke [ 22 Oct 2006, 13:05 ] |
| Post subject: | How-to: Better blacks on your LCD |
Read the link I posted |
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| Author: | Ryom [ 22 Oct 2006, 15:32 ] |
| Post subject: | How-to: Better blacks on your LCD |
As the coding values of the information used to display games & movies - is different... If you are referring to the fact that dvd movies dynamic range are compressed to fit within around RGB 15 to 240 or so, that changes nothing with regards to calibrating your black point. The lower and higher values are still there, they are simply not used. If you've got something like FFDshow installed, you can expand the values to the full RGB range if you'd like with the Levels options by dragging in the black and white point input sliders to the appropriate values, or use your DVD player programs color options. |
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| Author: | Ryom [ 26 Oct 2006, 09:41 ] |
| Post subject: | How-to: Better blacks on your LCD |
AVS Forum link Read the link for a very detailed post I made about this kind of calibration. |
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| Author: | skipclarke [ 01 Dec 2006, 16:49 ] |
| Post subject: | How-to: Better blacks on your LCD |
I added a link to this valuable info & gave you credit in my Tools: Screen Adjustment, Pixel Checking, Dial-in & More |
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| Author: | JvT [ 26 Jun 2007, 14:23 ] |
| Post subject: | How-to: Better blacks on your LCD |
To find out what settings I should use I did this: I taped a 4x6 matte black sheet of paper onto the bezel of my monitor so it stuck off the side (and wouldn't be illuminated by the panel) and I got my camera out (disable your flash!) and took a shot, where the image was exposed so that the black paper was just above full black... RGB 5,5,5 roughly. Could you please specify this part a bit? - Do you tape this black paper to the side or top of the screen (the plastic part, not the screen itself) so that the paper doesn't cover any of the viewable screen area? - Do you take a picture with your digicam in the dark so that both the screen and the black paper is seen in the picture? - how do you "take a shot, where the image was exposed so that the paper was just above full black... RGB 5,5,5 roughly." ? If you could either point to an URL with more specific text and pictures to explain, or take some pictures of the procedure yourself, that would help alot. The rest of the tutorial I think I can manage... |
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| Author: | Ryom [ 27 Jun 2007, 04:44 ] |
| Post subject: | How-to: Better blacks on your LCD |
Added to my first post. |
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| Author: | JvT [ 27 Jun 2007, 07:35 ] |
| Post subject: | How-to: Better blacks on your LCD |
Thanks a lot for your answer to my Q's. I got a better understanding of the procedure now :) |
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