Imitating color artifacting of Apple II text mode in GIMP text tools

[Schol-R-LEA]

I am attempting to recreate the sort of 'rainbow' color distortion found in the Apple ]['s composite color output. This is for a project where the text is supposed to resemble Apple ][ 80-column text on a color composite monitor; a similar project will also be done imitating a Commodore 64, but that doesn't present this particular challenge. The font I am planning to use is called "PR Number 3", though I am open to suggestions as to a font that more accurately mirrors the Apple ][ 80-column typeface. 

For those unfamiliar with it, due to the manner in which colors were produced on the Apple ][ in 'Hi-Res' mode, when using an NTSC television or a composite color monitor (which were essentially the same thing), creating a pure white image in most pixel alignments would create 'artifacting' resulting in green, blue, or orange hues in the white images, including text.

A more detailed explanation of this can be found on the YouTube channel "The 8-Bit Guy" (formerly "The iBook Guy", hence the outdated titling), who covers it in the video "Old-School Graphics, Part 2". I will add the video below at the bottom of the post for anyone who needs to reference it.  The video shows an example of the artifacting at 1:25, but it would probably make sense to watch the parts before it in order to understand the explanation.

So, my goal is to have a method for adding this sort of appearance, preferably automatically rather than by flattening the text layer and manually coloring the text. I would prefer to be able to edit the text with the text tool and have it applied automatically, or be able to re-apply it if that isn't feasible, while still retaining it as a text layer.

If there is an existing filter or script for this, please provide a pointer to it; otherwise, any advice on the best way to do this would be appreciated. I am willing to write a script for this myself, but I don't know how yet. An explanation for how this could be done would probably be best, as I would then be able to tweak it to my needs.

Note that I am not a graphic designer, and while I have used GIMP for a number of things over the years, I am a novice for all intents and purposes (though not particularly intensive purposes  ). However, I am an experienced programmer, and know both Python and Scheme, should the answer involve any Script-Fu coding. Please keep this in mind when answering. 

[rich2005]

I will throw this into the pot, just as a starter.

Saving grace here is the black background and fixed space typeface as Apple2 monitor. Real dificulty will be those slightly off colours.

Anyway, White text over black background
Suitably sized checker pattern on top and in Multiply mode
That would allow alterations to the text layer.

   

Bur still a good way off the required "RAINBO" effect

[Espermaschine]

Are we talking about some sort of pixel art here ?

You can work with a very small canvas size (like 20px for example), paint your image with a 1px sized brush, using the Pencil Tool to avoid antialiasing.
When ready, change the Image Mode to Indexed and use a limited number of colours (like 64 or 32 or whatever).
Then upscale the image to the desired size with Image -> Scale Image.

EDIT: i got it all wrong. Lets try this:

How about G'MIC -> Degradations -> Chromatic aberrations for a coloured haloeffect ?

This is what it looks like combined with the technique i described above.
Sans Font, 9px, upscaled.

   

[Schol-R-LEA]

(02-20-2018, 06:59 PM)Espermaschine Wrote: Are we talking about some sort of pixel art here ?

Not exactly; it is intended as a t-shirt design. The basic layout (scaled down to 400x100 px for the forum) is:

I took your advice, and took a look at the G'mic Chromatic Aberration filter, but then I noticed one that seemed even more appropriate: the CRT Sub-Pixels filter. I applied that, and got this: 

This is pretty much exactly what I wanted. Thank you, and thank Rich2005 as well; your advice really made this work.

Now I just need to figure out my tee shirt size in a women's fitted tee...

[Espermaschine]

Glad you found a solution !
Hopefully the filter transfers well when printed.

The image you posted reminded me of another tutorial by Irfan Prastiyanto, that does the same thing with a pattern.