The PAL luma mystery

On a NES PAL sytem, stylized horizontal gradient lines of the same brightness will blend into each other and create a richer colour presence, whether intended or unintended.

If two colours above/below each other are of opposite phase and equal brightness, the resulting colour should be gray.

However, i encountered a display quirk the other day – instead of a gray line, i got a black and white ripple. It seems as if *something* is causing the luma channel to oscillate between high and low.

comparison

before/after resolving the problematic effect

After a little experimentation, it turned out that this may be trigged or avoided depending on whether the change of colour is on an even or odd scanline.

I haven’t ruled out hardware deviance just yet, but simply nudging the border upwards solved the problematic effect.

PAL gamers will experience more colours in the sky for the ending scene of Project Blue. It wasn’t intended at first, but i think it looks quite nice.

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