This topic is now archived and is closed to further replies.


Display warping with pixel grids.

Recommended Posts

Heya -- I was adding a graphical layer to the background of a simple game I was programming.. It consisted of a gridwork of pixels, that alternated between black and white.. ie. like a chessboard, where each black and white square is the size of one pixel. For some reason the image was warping when it was displayed, like an oil+water effect.. there was slight colour distortion that came through in onion-skin like ripples. Just out of curiosity.. does anyone know what could be causing this -- the refraction of the light coming through the monitor glass perhaps ? - Scutt.

Share this post

Link to post
Share on other sites
it is an optical illision. It is the way the human brain works in "decoding" optical senses - ie what you see.

Lots of images do this, some are spirals, some are a bunch of squares, horizontal lines looking bulgy in the middle.
The colours are from the way the light waves reach the eye.

Ofcourse there is another option when using computers - you are using a tube, not a TFT, so your screen is actually bulging outwards. The colour is because you are using a tube and it isn''t aligned properly.
If it is digital you may be able to adjust it with the controls - otherwise you need to adjust the trim pots in the back of the case. If you have no idea how to do this DO NOT try it. Go and get a shop to do it.

Beer - the love catalyst
good ol'' homepage

Share this post

Link to post
Share on other sites
argh! not!

its no optical illusion, and its not any LCD effect.
its a CRT effect and comes from the "mask" of the CRT.

there are 3 rays fired that "scan" the display line-by-line (hence the word scanline ).
to "guide" these rays to their corresponding spots of red, green and blue phosphor, a "mask" (sheet of very thin perforated metal) is inserted just before the "screen".
the holes in this mask make sure

// this is "source" just to get me spaces and fixed-font ;)

*------------- "red" ray
| *-------- "green" ray
| |
| | *--- "blue" ray
| | |
\ | /
\ | /
\ | / ---> the 3 rays are moving in this
\ | / direction, this is just a "moment capture"
##### ######### ### - this is the "mask"
B G R B G R - these are the "phosphor spots"
(current) (next )
(pixel ) (pixel) etc.

since the "switching from one pixel-color to the next" that the graphics-card does is in no way synchronized with the occurance of the holes in the mask, and usually 1.3 or so holes cover one "pixel" from the gfx-card AND the "convergence" is not perfect on any CRT AND the R, G and B spots dont move "out of sight" for the triple-ray-beam, this effect is visible.

thats all.
buy a better CRT, one from EIZO maybe, or push resolution down to 640x480 and the effect will disappear.

--- foobar
We push more polygons before breakfast than most people do in a day

Share this post

Link to post
Share on other sites