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Old 20 April 2015, 02:14   #21
Newbie Amiga Programmer

Join Date: Jun 2012
Location: Front of my A500+
Posts: 56
Originally Posted by Mrs Beanbag View Post
my latest thinking is, one would want greater accuracy for the bright colours than the dark ones. So maybe one could start by only analysing the colours that have at least one component of 128 or greater. Then maybe you could pull off the least-useful bright colours one at a time and replace them with darker colours.
The problem is, if you reduce the brightness level, then it may result in colours which are undistinguishable for the human eye. If we increase the brightness, we may end in a lot of white-ish colour. But if we draw a line, that over this level we don't intensify, or under this level don't reduce, then the pixels gonna have different alterations, which will end in entirely different characteristics. (Besides a value of 128 is not bright. It's moderately dark.)

I think, instead of directly manipulating the channel values: a gamma increase or reduction should be done, then it can be quantized, then on the original (non-gamma corrected) image a color replacement can be performed, with the extended palette.
Originally Posted by Cylon View Post
But as you know ILBM is just one of many possible chunks in an IFF file. You could (trying to get really creative here) just create a new chunk with the alpha channel!! And save it into the very same file! Nobody gets harmed, everybody ignores what is unknown....
If everybody will ignore it, then what purpose it will serve, aside from drastically increasing the size of the output image?
On the other hand, on Amiga, there is no alpha channel, even the graphic cards supports only 24-bit bitmaps.
Originally Posted by Mrs Beanbag View Post
presumably "alpha" can just be regarded as another component in the palette entries, i assume ILBM packs the 12 bit palette entries into 16 bit words so one could use the upper 4 bits for alpha anyway
Nope. ILBM always store the RGB components on 24-bit, but the OCS/ECS machines ignores the lower nibble of the channels.
Originally Posted by wXR View Post
What is yours, if I may?
Sorry, but no, because you won't believe me and i don't want to engage in an unnecessary and pointless flamewar.

Last edited by jsr; 20 April 2015 at 02:18. Reason: word replace
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