Artifact when using CRT-Aperture mask

RetroArch Additions Shaders
#1

Does anyone know why this happens when I set the mask strength higher than 50%?

mask at 50%:

%20(W)%20%5B!%5D-190804-122706
Super Mario Bros. (W) [!]-190804-122706.png1536×1120 105 KB

mask at 100%:

%20(W)%20%5B!%5D-190804-122716
Super Mario Bros. (W) [!]-190804-122716.png1536×1120 86 KB

EDIT: I’m wondering if the mask is actually doing something weird with the LCD’s subpixels when set higher than 50%. When I zoom the second image to max size, I see weird horizontal bars extending across the entire screen, beyond the actual image… The bars are most prominent at the top, middle and bottom of the Super Mario Bros. logo. Also, if I defocus my eyes and look at the second image fully-zoomed in, I can almost see the screen refreshing, almost like CRT flicker. Weird! I’m using a 1080p TN LCD.

#2

Nothing looks abnormal from here. You mention a 1080p display but the screenshot is 1120px tall, so I’d expect non-integer scaling artifacts, especially with that bright-pixel-black-pixel mask pattern. (Disregard if you’re certain you’re getting 1:1 pixel display.) If you’re seeing something inconsistent with that… well, can you get a photo of the monitor’s output?

And yeah, flickering effects with tight contrasty patterns on TN panels… not uncommon at all, sounds like https://en.wikipedia.org/wiki/Frame_rate_control

#4

It’s at 5x integer scale, so the problem isn’t related to scaling; the excess pixels just get cropped off.

Here’s a photo taken with my cell phone:

IMG_0485
IMG_0485.JPG2851×2138 3.24 MB

Those bars aren’t visible if the mask is set to 50% or less. Something about it being higher than 50% does something weird to the LCD’s pixels.

#5

ah, yeah, that’s definitely not visible in the screenshots, so something about your LCD not liking the pattern.

1 Like
#6

This is an LCD pixel inversion artifact. All LCDs suffer from this, but in different ways (for example one monitor might produce severe artifacts on one image, like in your case, but another monitor might be OK but then produce such artifacts on a different image.)

More details: http://www.techmind.org/lcd/index.html#inversion

The image you posted produces the same results on my monitor (I use a 1440p IPS monitor) but only if I zoom it out in my browser, and only one specific zoom level. TN panels are the most affected by these artifacts.

3 Likes
#7

I have this same exact problem on the Samsung Smart TV in my Den. I was never able to correct it unless I adjusted my sharpness settings on the TV which made the image ugly.

#8

Very interesting, I think I may have seen this on my old tablet when doing some brief testing with RA.