Gamma-adjusting-chip?

[Rockard]

.. to output the rgb signals into some sort of chip with a pot, that then outputs a modified signal? Is it possible? Does such stuff exists as hardware somewhere?

Thanks
/Rickard

[Aidan]

Yes, it's possible, but it would require a bunch of circuitry to do it. You could do it with a ADC/ROM/DAC on each channel fairly easily. If you wanted multiple gamma curves, then you could set up several tables on the ROM.

Basically, the way such a device works is that it converts the analog value into the digital domain (IE, into 8 bits). That value is then passed to the ROM as a memory address, and the ROM outputs the value stored in that address (Table lookup). The output from the ROM is then passed onto the DAC which converts the new value into analog form.

As each table would only store 256 values, there are a few tricks you can pull with memory addressing to build multiple tables and be able to select between them. An 32K ROM chip could store 128 tables easily.

Obviously you'd need three times this, one for each channel.

As for a single chip that does it, there are video pre-amps like CXA2153S and TDA4780 that handle gamma correction onchip, but it won't be as simple as connecting a pot up. You'd need to load the gamma tables onto the chips digitally at start up.

[Vertigo]

May not be entirely what you're looking for but the general practice with things like Super Guns and such like are that you have your 3 R, G and B outputs and they have pots on them to control the output strength of each, which essentially controls how bright or dim the signals are.
While this isn't exactly gamma correction, it still goes some way to boosting a dim signal or dampening overly-strong colour signals such as those outputted by CPS2 and System11 boards. Wouldn't want to make my telly go pop now, would I?

[Rockard]

Thank you very much, Aidan and Vertigo!

Vertigo: What you described here, I have already tested. But it didn't work as expected, but thank you very much anyway.

Aidan: Can you possibly write up a little diagram? Any software needed? Chip programming involved?

I am not really that good with electronics and programming, as I only understand how things work in theory. I do have basic programming and soldering skills, but not enough to build this myself. But with some more info I can cooperate with my brother and build it.

What I need it for? Well, it is my RGB-modified-NES that I think would have a more accurate A/V-looking palette with some gammaadjusting. =)

Thanks for any help!

/Rickard

[Moosmann]

What I need it for? Well, it is my RGB-modified-NES that I think would have a more accurate A/V-looking palette with some gammaadjusting. =)

Oh no, the RPG NES
@ Rockard: I send you some photos this weekend sunday.

Bye Markus

[Rockard]

Agh! Leave me and my beloved rpg-nes alone!

(looking forward to the pictures.. yummy..)