2004.01.14 19:02 "Re: [Tiff] COLORMAP and byte padding", by Andy Cave

Hi Marti.

What "significant errors"? Please show us. As far as I know there are no significant errors - as I said in my previous post, 0 to 255 -> 0, 256 to 511 -> 1, etc... gives an even spread reduction. How else would one want to map these numbers? For example what do you think 127 should map to, or 128, or 255, 256, or 511,512, etc...?

Your calculation is:

(rgb * 65281) = (rgb * (65536 - 255)) = rgb * 65536 - rgb * 255.

If I understand this correctly, all it does is map 0 to 128 -> 0, 129 to 385 -> 1, etc... which gives a non-even spread (where the end 'bands' are half all the other bands). Why would anyone prefer this (slower method)?

_andy.