One colour per photosite
A real 32×24 crop straddling the border between a colour chart's blue patch and its green one. The lab filters it the way a Bayer sensor does — one channel per pixel — then reconstructs the missing two from the neighbours and differences the result against what it started from.
Try this
Step to the error view. The flat interiors are almost perfect and the one-pixel boundary between the patches is where it all goes wrong, which is why colour fringing shows up on edges and never in the middle of things.
Where this lab comes from
Sensing Colour: The Bayer Mosaic, and What Interpolation CostsLesson 5 of Image Sensing. A silicon photosite is colourblind, so a mosaic of filters gives each one a single colour — a quarter red, a quarter blue, half green. Two thirds of every colour image is therefore interpolated, and measured against photosites that actually exist, that guess costs 4.7 DN on a flat patch and 129.9 DN at an edge: twenty-eight times worse where it shows.
More in the image itself
- Hitting the colour a meter measured — Drag the gains and watch ΔE against 22 metered patches.
- Sixteen by twelve real pixels — Hover a pixel, read its index and its three numbers.
- Sampling, and the pattern you get instead — Sample a wave too coarsely and a different wave comes back.