Color fringing in B/W images
Phil Pilgrim (PhiPi)
Posts: 23,514
When the Propeller is outputting grayscale video data, medium to large transitions in luminance can cause color fringing at the rising or falling edge. I believe this comes from luminance-to-chrominance crosstalk in the video monitor that results from the sharp transition's high-frequency components. What I'm wondering is whether there's a way to eliminate the fringing without killing the color altogether (short of going to S-video). Simple capacitive filtering doesn't work. At the point where enough capacitance has been added to reduce the fringing, there's too much horizontal blurring. Are there any simple remedies I'm overlooking?
-Phil
-Phil
Comments
I guess display cannot tell if the transition is a change in luminance or a change in chominace until it stays at that level for a little while (longer than the colorburst freq I guess).
I haven't played with the video generation code yet, does it only have four colors ? The posts I remember seeing only had black,white, orange, and blue (ala Apple).
Bean.
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1. A color palette consisting of four colors, each selected from 96 HSB combinations, plus 6 gray levels and a sync level, expressed as four bytes packed into a long.
2. A vector of 16, 2-bit indices or 32, 1-bit indices into the color palette, depending on the video mode, and expressed as a packed long.
The available colors are, for the most part, lightly saturated with five luminance levels. Sixteen of the the 96 colors are fully-saturated and 180 degrees out of phase with their more subtly-colored brethren. In each case, the colors cover the hue gamut in equal intervals of 22.5 degrees. Conspicuously absent, though, is a pure yellow. This is just a consequence of the way the chroma phases are partitioned and the fact that "yellow", as we know it, occupies such a narrow range of the visible spectrum.
In the Graphics object, the screen is divided into a 16 x 12 array of tiles, each tile having 16 x 16 pixels. Each tile has an associated color palette of four colors, chosen from the 102 colors available. Each pixel in a tile can be one of the tile's four colors.
-Phil