Quoting myself from earlier in the thread:

A single artist will likely rasterize the same size ellipse in different ways in different situations, based on what they're depicting and the colours they're using.

Context matters. A person's "opinion" on which pixels to fill with which colour depends on the context. Sure, if someone's just filling out a sheet full of contextless ellipses, then it's only their opinion that matters because there's no context. But the point is, most people don't do that, they do ellipses in context, and that context drives their decision.
If you pixel ellipses the same way in all contexts, you're probably making worse art than you could be.

You don't need to post a pre-zoomed version, Pixelation has a zoom tool. Click to zoom in, ctrl+click to zoom out.

I think this is a very solid start! I have mainly minor nitpicks:
- The shoulder has jaggies, and the white area below the shoulder is conspicuously missing AA.
- I like how most of the face is in shadow, but it seems like the nose shouldn't have that highlight on it, while the cheek should have more light.
- The shape of the sideburn (not sure what to call it) is jagged and feels a bit tentative, I think some smoother, swooshier curves would look better. The shading/AA on it also hug the lines, creating banding.
- The AA on the light part of the uppermost hair spike and the top of the head uses too dark a colour and just makes the outline look thick.

Don't know what API/version you're using, but OpenGL's Image Load Store is handy for this kind of thing. So long as you are operating on pixels independent of their neighbours no need for for a copy and bypass sampler nonsense, can bypass all the render-to-texture nonsense too if you use compute shaders. D3D has an equivalent too but can't remember the details that'd be RWTexture*.

Using OpenGL, and that's handy! I decided not to do the darker color shader because even with that it's more hassle than it's worth it to me xP But I'll probably find a use for that in the future when I'm more comfortable with shaders in general. Sticking to really basic stuff for now.

More OpenGL shader ???ing, in case anyone's in the mood to read about a noob struggling with the basics!
I'm playing around with applying color maps and I've just broken my brain. As far as I'm aware, OpenGL texture coordinates have their origin at the bottom left, and that's how it's worked so far. I am using this colormap for testing:

It has its origin at the top left, and the y coordinate corresponds to green (high y = high green). So, this should mean that in my shader where the origin is at the bottom, high green should mean low y, achieved with y = 1.0 - green:
vec2(pixel.b/16 + floor(pixel.r*16)/16, 1.0-pixel.g)But that makes a mess, and it seems I should be directly using green as my y coordinate:
vec2(pixel.b/16 + floor(pixel.r*16)/16, pixel.g)This gives me the desired results (hardly any visual change to the image). Am I misunderstanding something? Having a brainfart? When the green component is 0, I'd expect that second coordinate to mean the bottom of the color map, so why is it giving me the top?

Edit: Maybe it's something to do with SFML and how it handles textures? Now that I think of it, I think my previous attempts also had y = 0 at the top, it just didn't matter as much on those so I didn't notice.

I tried writing a shader today to do Photoshop-like "darker color" blending for 2D rendering, and never again. Since I can't sample the existing buffer safely, I have to make a copy between each "layer", which requires restructuring some otherwise perfectly fine code in a way that makes it worse (I have to use textures everywhere to be able to sample from them, instead of using more general render targets), and I got stuck trying to get the correct position into that copy anyway, so I just decided to make do without it.
I might still play around with shaders for other purposes, but multi-layer multipass rendering requires more caring than I can currently muster. I can do single-pass stuff, and I can do post-processing after everything is rendered. That's enough.

Zizka, the lighting on the sphere is from the upper-front-left, but the shadow is directly to the side and rectangular, which is probably why the whole thing doesn't feel right to you.