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Human perception - aliasing?

Started by Butter Mar 10, 2003 at 12:41 PM 3 replies 1k views
Original Post
Butter
Butter
I am drawing a sphere textured to look like the earth. The texture is two tone (blue for water and tan for land). Above the earth I am drawing an orange line. The lines appear to be orange when the tan land is behind it, but it appears to be pink when there is blue water behind it. The line also appears thinner when the blue water is behind it. I would like the line to appear to be the same color everywhere! I''m thinking that this is due to aliasing - kind of dithering the background color with the line color. ???? Any ideas on how to fix this? I don''t want to increase the width of the line (although that would probably help). I''m not using any anti-aliasing - would this help? Any help appreciated, butter
Yann L
Yann L
Aliasing is the effect where your line is not smooth, but pixelated, due to the finite resolution of the screen. It makes your line look blocky, but it does not change the colour.

Dithering could do that, but on what kind of 3D hardware are you running ? No hardware running in 24bit colour will show that effect, and even on dithered 16bit cards (old Voodoo''s), the colour change was never really noticeable (besides in gradients, and when blending, of course).

To be sure that it''s no a technical problem, just take two screenshots, load them in Photoshop, zoom in, and compare the colours. If they are the same, you''re basically left with two possibilities:

It could be a problem with the RGB guns of your screen not being focussed like they should (if you have a CRT, doesn''t apply to flatscreen displays). Test on a different screen to check.

Second (and highly probable) possibility, is that you are actually experiencing the effect of colour bleeding - in your eye/brain. It''s a both a biological and psychological effect. The human eye has limited colour resolution, if two very nearby colours have high contrast (the very different signals generated by the nearby retina cells can interfere). And the ''processing'' your brain performs on the image can also lead to that kind of problem (optical illusion). The only solution is to increase the line width, or to reduce the colour contrast.
Butter
Butter
Thanks Yann L. I have changed the colors on the earth and this has eliminated the color-bleeding problem that I was seeing. Hopefully I won''t have to many more problems like this, as I have many more artifacts to display - all must be represented with a different color.

arsenius - Sorry, can''t post any screen shots as this could possibly lead to termination of my employment!

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