Originally Posted by pandy71
Or in other words - there is no good picture converter supporting "dynamic" color changes - compared to ST Amiga can use Copper and CPU so results should be superior, with modern color quantization algorithms this should push Amiga to very high quality conversion IMHO.
My converter could do this. There's two approach to quantize an image to a copperlisted ILBM.
One is to quantize the image per N line pieces. This would result in a [(height / N) * no_colours] coloured image, which can be even more than 256, for example a 200 pixel tall picture quantized to 32 colours per 16 line would result in a 400 coloured picture. However, this can result in a slightly "striped" image, as the colours can differ in each N line tall stripe.
Second is to specify the limit of colours (N), then begin to count colours from the top left corner. Whenever in a line, this colour limit is surpassed by X number of colours, then a copperlist entry would be made, with X palette entries changed to the new colours. This method would produce a result identical to the original image, however this method assumes, that the relevant lines don't contain more colours than N-X, which is highly unlikely to happen in a picture, which have very much colours. The picture can be quantized first (for example to 256 colours), but then the other method can result in higher colour numbers. But this method will still won't produce stripes.
However, any method requires a copperlist chunk in the ILBM and a viewer, which can use it. Is this special chunk defined in any ILBM standard? I know about PCHG, but is that used in viewers?