Very Slightly OT: Help Recaclulating HEX color codes?

Oldbitcollector (Jeff) · 2008-03-20 14:30

I'm working with a spin program which reads .XPM files which contain color entries that
look like this: #000080800000", #0000FFFF0000", #000080808080" (Hex RGB)
I'm failing to come up with a reducer calculation which would lump all shades of
white as #FFFFFFFFFFFF.

Without letting too much out of the bag, I have 64 colors to get to.

Has any done other work with RGB colors to have a decent solution I
could implement in spin?

Thanks
OBC

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big_mark · 2008-03-20 15:33

The quick way of doing it would be to take just the two most significant bits of your red, green, and blue values, and combine them into the lower 6 bits of one byte. To do this do the following

For the red component :
  Read the most significant byte (we don't need the least significant byte at all)
  AND it with 0x11000000 to get just the two most significant bits
  Shift the result right by two places

For the green component :
  Read the most significant byte 
  AND it with 0x11000000 
  Shift the result right by four places, not two!
  OR the result with the red value

For the blue component :
  Read the most significant byte 
  AND it with 0x11000000 
  Shift the result right by six places, not two or four!
  OR the result with the combined red/green value

This will give you a six-bit value for your RGB colour and it assumes that your palette is set to match it (e.g. 0x00110000 gives full red, and 0x00111100 gives yellow, etc)

If you must keep your 'two-bytes-per-component' structure, then instead of shifting and OR'ing your results do the following :

For each component :
  Read the most significant byte 
  AND the MSB with 0x10000000 
  If the result is 0x10000000 
    then set the high byte of the component to #FFFF 
    else set it to #0000
  AND the MSB with 0x01000000 
  If the result is 0x01000000 
    then set the low byte of the component to #FFFF 
    else set it to #0000

Hope this helps

Edit : Since you are reducing from over 281 trillion colours to just 64, expect some loss of detail!

Post Edited (big_mark) : 3/20/2008 3:53:03 PM GMT

Oldbitcollector (Jeff) · 2008-03-20 18:54

Wow.. You've got my head spinning.. [noparse]:)[/noparse]

I've managed to reduce the source codes to three hex digits,
which should help. white is now #FFFFFF instead of #FFFFFFFFFFFF.

Thank should help... Just looking for a big glass of watch to
swallow that explanation with.. [noparse]:)[/noparse]

Thanks!

OBC

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New to the Propeller?

Getting started with the Protoboard? - Propeller Cookbook 1.4
Updates to the Cookbook are now posted to: Propeller.warrantyvoid.us
Got an SD card? - PropDOS
A Living Propeller FAQ - The Propeller Wiki
(Got the Knowledge? Got a Moment? Add something today!)

Post Edited (Oldbitcollector) : 3/20/2008 8:36:41 PM GMT

Very Slightly OT: Help Recaclulating HEX color codes?

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