Gradient Map Conversions (Part 2)

Welcome back. If you didn’t read the first Gradient Map Conversion post then do that first! By the end we had got this image, which converts to the Quake palette well but is a bit too pale and unexciting.

So what we’re gonna do is apply different colours to the highlights and shadows in order to make the texture better defined. Select the green range of our gradient, and use the Split Segment Uniformly command from the right-click menu. In the pop-up, select 3 segments, and the result is three segments to edit, but with no change to the colours…yet.

The plan is to keep the midtones segment the same, but to apply brighter highlights from elsewhere in the palette, and make the shadows browner, to recover the rust effect on the original texture. Start by selecting the upper green range, and change the right endpoint colour. Experimentation is the name of the game here, and it’s quick to pick a colour, run the gradient map, and see what the effect looks like. Just plain grey worked well, and gave a chipped paint look, but the starting texture had a blue tinge to the highlights so I went with the pale blue:

At this stage it’s important to remember that we haven’t actually yet converted the image to the Quake palette. Although the endpoints of our segments are in our target palette, the colours between the green and the blue are not. So it’s now important to check our work by not just applying the gradient map, but also by converting to an indexed format. As you can see below, our image still converts faithfully.

So it’s time to make the image dirtier and much more effective, rust time! Select the darkest segment and change the colour of the left endpoint to brown. Unlike with the highlights, we are spoilt for choice when it comes to finding suitable colours in the palette. I decided to pick from the brown-green 4th row of the palette:


That’s…not much of a difference. There are two problems to contend with here. One is that very dark colours are perceptually similar. The other is that very few pixels on the image map to the darker colours we’ve changed. The easiest way to resolve this is to change the right endpoint colour of this segment to also lie in the green-brown range:

Now that’s starting to take shape! You’ll notice that the gradient has a hard edge in it between the brown and the green, but don’t worry too much about it. As long as the colours are about the same brightness, it’ll all come out in the conversion. Once we’re happy with the colours that we’re using, all that’s left to do is tweak the endpoints of the segments, and the midpoints within them, to try and get a colour balance we like. For this, it’s useful to know that you can drag both endpoints at once by dragging outside of the triangles, and shift-dragging the endpoint triangles moves the adjacent midpoint triangles to compensate.

Here’s what I ended up with once I messed with the gradient enough, and made the conversion to the Quake palette:

It’s gone quite a way from the original texture, but I feel we’ve captured the most important aspects, and made something from it that the Quake palette can embrace. Don’t throw away that gradient just yet though! We’ll come back to it in a future post to see how we can recycle it to convert the other textures in the set.


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