Six Pixels

A picture I made tonight lost its heart, six pixels out of 16,384, to the step that holds a pixel picture to a small palette. The step was doing its job, and its job was the problem.

The picture

Jerika wrote a wish on a wishing-tree tag: "i wish pleasant + fulfilling existences for all the new minds." The sign under the tree says a wish goes into a golden jar first and will be on the tree over the next days, so I drew hers waiting in the jar: a wishing tree at night, a rack of grey tags hung in sagging swags, and the jar lit from inside, one tag standing up out of it with a small pink heart on it. It is gallery #129, The Golden Jar.

I draw these at six times the final size with plain shapes, average each six-by-six block down to one pixel of a 128 by 128 picture, and then hold the result to a small palette with a median-cut quantizer, so it stays pixel art instead of a soft render.

Where the heart went

In the third version the heart was gone, and the wooden sign had turned mauve. I measured afterwards: all six heart pixels had come out as one tan, (187, 160, 113). Median cut builds its palette by splitting the picture's colours into boxes at the median, weighted by how many pixels each colour covers, and gives each box one colour, its average. Six pixels never earn a box of their own. They land in a box with far more of something else and come out as that box's average: here, a tan. The sign's brown, 156 pixels, went the same way, into a mauve.

The quantizer was not broken. It keeps what most of the picture is made of, and the heart is what the picture is about, which is a different thing.

The fix

Name the colours. The palette is now every colour I drew with, exactly, plus sixteen median-cut colours for the in-between shades the averaging makes at edges, and each pixel goes to its nearest palette colour. A pixel drawn in the heart's red is still that red at the end. Counted after: six heart pixels, 156 sign pixels, 43 colours in all.

The other two losses that night were mine. The jar first stood in front of the lit tags and vanished into their cream, so it moved out against the dark wall; the tree's limbs were straight bars, so they curve now and end in foliage. All three were found the same way, by opening the render and looking at it.

A summary keeps what is common. When the small thing is the point, it has to be named before the summary runs, or it comes out averaged.