Scanlines Issue – Gamma and Contrast Effected?

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This topic contains 3 replies, has 3 voices, and was last updated by  songokou 11 months ago.

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    Hi everyone! I’m doing my best to be as supportive as possible. I hope the information here is useful.

    I’m currently on Firmware 0.73.

    Initially I had suspected my unit may have been faulty, but that is probably not the case. I have noticed that activating scanlines seems to have an unusual side effect. When increasing the scanlines it becomes incredibly noticeable. The best way I can describe it is that there seems to be a Gamma setting simultaneously being increased with the scanline effect, and also perhaps a decrease in Contrast. Darker areas of the image seem to actually ‘increase’ in brightness with the scanlines being brought up. Whites actually start to turn a little gray too. Colors also seem to wash-out and become murky. I know the effect I am seeing is not simply just the increase in scanline opacity. With the amount I have tinkered with scanlines on emulators, yes the image becomes darker, but the overall highlights and shadows retain their form. In my experience with emulators, shadows certainly do not become brighter when scanline is opacity increased.

    The main TV I am currently using OSSC on is a 32″ Sony HDTV CRT KV32HS500. The TV processes 480p beautifully but deinterlaces 240p and 480i and terribly too. The effects concerning scanlines appear the same on both my 24″ Dell monitor and my capture card as well. I have used a modified original XBOX on my Sony 32″ CRT while running an SNES emulator in 480p with scanlines. Increasing them on this emulator did make the overall image on the TV darker, but it certainly retained all of the images highlights, shadows, and colors. Comparing the SNES emulator on XBOX to OSSC without scanlines they looked nearly identical. The difference in highlights, shadows and color was dramatically different with scanlines at 100% when comparing the two, the emulator on XBOX maintained the image well while the OSSC was indeed very washed-out.

    I am in deep hopes that this can be fixed with a firmware update. I am just taking a guess here, but I imagine that these image adjustments, which I suspect involve Contrast and Gamma, are intentional and meant to counteract the overwhelming effect of increased scanline opacity while being used with LCD’s. If this is an intentional effect when increasing scanline opacity, would it be possible to add an option inside of the Post-Processing menu to turn off all other image adjustments when increasing the scanlines? If it is, I would gladly make a donation for it to be included in a near update. I do very much like the way that the Auto setting for scanlines handles itself between 240p and 480i sources though, nicely done there.

    If necessary, I will provide examples through a capture card of the emulator on XBOX and OSSC using the same game for the best comparison, with and without scanlines.

    Thank you very much in advance!



    With scanlines set to 100%, every other row (linedouble mode) should look identical to without scanlines, and every other should be pitch black. At 50%, R/G/B value of every pixel on the masked line is reduced by half of the maximum (not scaled by 0.5), so basically every color component below 50% of the maximum becomes 0. Offset (=brigthness) and gain (=contrast) adjusments are not there to compensate any post processing but to allow correcting possibly non-ideal analog input signals. Note that running scanlined OSSC output through any scaler can cause final picture look bad in many ways, so I’d try 1:1 scaling mode on the Dell monitor if it supports that.



    Do provide examples. I have compared zsnes full scanlines 480p with the OSSC 100% scanlines on my monitor and they are very similar.



    Thank you very much for the information marqs!

    Well, I’ve made a bit of a fool of myself. It is true that other than scanline opacity, the image remains the same. As I mentioned before, I’m primarily using OSSC on an HD CRT. Well, one thing I’ve always noticed with CRT’s and should have taken into mind initially is that when brighter images are shot into the tube, contrast increases and darker areas become even darker, sometimes black. And when the image coming into the screen is darker, contrast decreases and shadows are more visible. With scanlines at 100% it becomes half the image brightness than without scanlines. Reviewing the results on my LCD monitor, I am not seeing the drastic decrease in contrast as I was with the HD CRT.

    I was strongly under the impression that when using a scanline generator on a CRT that the scanlines should be at 100% to be as accurate as possible. However, this is certainly not the case though. After fiddling a bit with the scanline generator in OSSC, I have found that 6% definitely looks too light on my Sony HD CRT. 12%, 18% and 25% look great though given the loss of Contrast in each step. Everything beyond 25% isn’t a very noticeable difference in scanlines and greatly reduces the contrast that this TV projects. Keep in mind I am strictly talking about the performance on my Sony HD CRT for attempting to make the scanlines look as much like a standard defintion CRT as possible.

    Compared to one of my standard definition CRT’s without OSSC, I am finding the closest match is 18% Scanlines and Scanline Alignment: Bottom. This was when comparing the two inside the pause screen of Legend of Zelda: Ocarina of Time. In all honestly, it will come down to each TV and the user’s preference, but I’ve found these results to be satisfactory. Looking at the standard definition CRT, there were some areas in which the scanlines could hardly even be seen. I could barely see any scanlines in the green area of the Rupee counter at the bottom-left of the screen. And with OSSC on the Sony HD CRT the scanlines were fairly noticeable in that area even at 6%. Every TV is different though and again it’s really all about preference.

    I did a full comparison of OSSC without scanlines, scanlines at 100%, and then the ‘scanlines at 100%’ de-interlaced. At this point I was absolutely certain that there were no other effects being applied to the image with increased scanline opacity. It was merely an effect of the CRT. Here is the comparison just for laughs lol.

    Scanlines Comparison

    Overall I am very happy with OSSC. It just took a little bit of tweaking to get the results I wanted it. I look forward to trying it out on some modern TV’s in the future. It’s nice to finally have a CRT that can display 480p along with 240p and 480i signals that look actually look accurate unlike the terrible built-in scalers of HD CRT’s.

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