To be black or not to be black? color question

[Aloan]

(very noobie question alert)

So I have a curiosity question that I guess only in here will I find the answer!

 

Is the black color necessary on the Atari 2600? if there is no color then isn't the screen black in itself without the need for color?

 

I have read somewhere that when the tv beam is off (no code entered), it does not produce a color (why that is obvious) so why is there a black color (on its NTSC palette), if black is not even writing a color (or turning on a color)?

Edited October 24, 2015 by Aloan

[Kiwi]

Stay Frosty 2 or Space Rock option screen comes to mind and Spiceware had an explaination about that. If you tune your TV screen in a certain way, you could see gray colors instead of black. It basically transparent color. I assume if you had attached another graphic stuff to the unit, you could see through that while black would block the picture.

 

It could be like this Laserdisc player coorperating with the MSX graphic chip, which color 0 is transparent while it does have color black which is color 1.

https://youtu.be/1l1BK53mFvw?t=16m9s

Edited October 24, 2015 by Kiwi

[+SpiceWare]

If you turn off the video signal you'll get a black that's darker than black. You can see the difference on screens with the brightness and/or contrast set too high.

You can see that in The Story of Stay Frosty 2, Part 13 at the end of the section titled Menu Graphics.

[Thomas Jentzsch]

Sometimes you display black objects over a colored background. There you need black.

 

And it is more easier to have all colors available (incl. black). Else you would need special cases for displaying black.

[Jess Ragan]

I thought this was going in an entirely different direction, honestly...

[ZylonBane]

And what, my fellow Romans, would anyone possibly need this savage "zero" for? Numbers are for counting things, not nothings! If I have none of a thing, then I would not be counting it in the first place. Foolishness!

[Aloan]

I understand now, thank you all for responding! I thought that just turning off the beam would save some memory! (which I guess does! but you will have a fake black color aka dark grey as shown in Stay Frosty 2)

Edited October 28, 2015 by Aloan

[SeaGtGruff]

You also need a black color, rather than just the blanking, because you can't turn blanking on and off fast enough to draw pixels with it. It takes a minimum of 3 CPU cycles to turn blanking on or off-- it could take longer if you need to load the A, X, or Y register first-- and each CPU cycle is 3 color clocks wide, so the smallest "pixel" you can draw this way (by turning blanking on, then immediately turning it back off) is 9 color clocks wide.

 

There's also a limitation on where you can position these "pixels," because they can start only on every third color clock, since shifting the machine code by 1 CPU cycle corresponds to shifting the "blanking pixel" by 3 color clocks.

 

Additionally, if you "draw" a background with the blanking this way, you can't move anything across it-- e.g., a spaceship flying through space-- because the raster beams can't draw the spaceship if they're turned off.

 

And finally, if you "draw" anything with the blanking, you have to figure that into the timing and sequencing of everything that's going on in your scan line loop, because you can't just set some graphics register to a desired shape and color during the horizontal blanking and let the TIA automatically draw from that graphics register at the appropriate place in the scan line.

 

So you can definitely "draw" with the blanking if you want to, but there are severe limitations.