color alignment issue

[Joey Z]

I have an atari 400 w/ a GTIA (not sure if this matters) and when I plot a single white pixel on the screen in BASIC, (hue 0, luminance 14) the pixels red color is sometime offset to the left making the pixel green or the blue to the right making it purple. when I put two pixels next to each other, one pixel becomes white while the other still looks wrong. Does anyone think the composite video modification would solve this?

 

The attached picture is of a "white" pixel in the middle of the screen in GRAPHICS mode 8. it is hard to see but the blue is separated out to the right

Edited February 12, 2011 by Joey Z

[Rybags]

GTIA - it does matter.

 

Single pixels in hires give artifacting, it was used in some games for more colour.

 

Should be normal on an NTSC system, PAL gets "kinda" artifacting but it looks crap.

 

CTIA and GTIA give different results for artifacting, general opinion seems to be that CTIA looked better, but GTIA is by far the more common and useful chip to have (although CTIA chips would fetch good bucks on the open market).

 

To try it out, try drawing vertical lines single-pixel wide with one blank inbetween. Do it on even and odd pixel boundaries.

 

 

Composite video will still give artifacting - using S-Video is the way to get rid of it.

Edited February 12, 2011 by Rybags

[+Stephen]

I have an atari 400 w/ a GTIA (not sure if this matters) and when I plot a single white pixel on the screen in BASIC, (hue 0, luminance 14) the pixels red color is sometime offset to the left making the pixel green or the blue to the right making it purple. when I put two pixels next to each other, one pixel becomes white while the other still looks wrong. Does anyone think the composite video modification would solve this?

 

The attached picture is of a "white" pixel in the middle of the screen in GRAPHICS mode 8. it is hard to see but the blue is separated out to the right

This is why the standard font was designed the way it was - it will always have vertical bars of 2 pixels width to avoid this problem.

[Joey Z]

these are pictures of the even and odd vertical lines as well as the program that showed me the problem in the first place. it is a forier series analysis demonstration my dad wrote on an IBM PC XT 25 years ago that I ported to atari basic.

 

so adding s-video would solve this you said?

Edited February 12, 2011 by Joey Z

[Rybags]

Run S-video, or just turn the colour/saturation down on your TV.

 

S-Video will improve your picture quality a great deal, so it's worth the effort anyway.

[+bob1200xl]

Nice Fourier program... will you post it?

 

Bob

 

 

 

these are pictures of the even and odd vertical lines as well as the program that showed me the problem in the first place. it is a forier series analysis demonstration my dad wrote on an IBM PC XT 25 years ago that I ported to atari basic.

 

so adding s-video would solve this you said?

[MEtalGuy66]

That's all completely normal. In fact some games rely on this to generate colors..

 

Composite video will not "fix" this.. S-video will..

[Joey Z]

if anyone is still interested the forier program is listed below:

 

10 GRAPHICS 24
20 SETCOLOR 1,0,14
30 SETCOLOR 2,0,0
40 DEG
50 COLOR 1
60 FOR A=0 TO 319
70 Z=0
80 FOR F=1 TO 17 STEP 2
90 W=(1/F)*SIN(F*(360/319)*A)
100 Y=INT(192-(95.5*(W+1)))
110 Z=Z+W
120 PLOT A,Y
130 NEXT F
140 O=INT(191-(95.5*(Z+1)))
150 PLOT A,O
160 NEXT A
170 GOTO 170

 

My dad made this when he was in college and it was originally written by him for an IBM PC XT with EGA graphics I think. this one is based off of a port I did for my calculator actually. the original used the WINDOW command which would let you use the screen like graph paper but my calculator did not have this and neither does ataribasic. since I made the calculator port first, all I had to do was change some of the values that were screen specific (mainly resolution related) and it worked. my dad also had the program draw the square waves that the added wave would become but i have not got around to that. you can add a STEP .5 to line 60 to make it twice as accurate and twice as slow.

Edited February 18, 2011 by Joey Z

[Joey Z]

if it doesn't work please tell me. it is probably just a typo.