RGB Decoding

If your talking about returning a single component from a 32 bit RGB value (int/long etc), you need to bitwise AND your Colour with 255 (to power r=1,g=2 etc). It looks like you have got your operations mixed up.

I would guess (I don''t use delphi):

DecodePixel := RGBval and (255 to power RGBComp)

A quick search on google confirms ''and'' as a bitwise AND unless enclosed in parenthis in which case it acts as a logical AND. This would probably be your ''If'' problem.

,Jay

it appears there was an objecion on the part of the compiler to me doing it all in one line of code (which''ll teach me to be a smart ass.

It seems to like it in the following format:

a := RGBVal [Integer Div] 256 [Power] (RGBNum -1) ;
a := a and 255

so if I split the lines it works well enough.

cheers m8

~~tim

Red:=RGB and 255;
Green:=(RGB shr 8) and 255;
Blue:=(RGB shr 16) and 255;

Generalized function:
Value:=(RGB shr ((RGBComp-1)*8)) and 255;

Of course that mul (*) is slow, so you could use either a precomputed array[1..3] or a case(not if) statement.

but the mul should be replaced by a (shl 3) if the compiler optimier is worth anything. or you could change it yourself (since all the calculations should be integer math anyway. using a case/if/array is slower then a single multiple.

also the RGBVal does not need to be checked since it will always be valid even if the 4th byte contains some garbage value. this helps quiken the conditional statment. though i think you should remove the conditional statement completly since this is a pixel function that will be called numerous times (in fact probably so much that you may want to not use a function for this) that you will greatly reduce your speed.
in cases like this you should take care that your calls dont use the wrong value, instead of placing gaurds that will probably never be used at all (first checking to see if the values are within bounds, then checking the function call return to make sure that the value was good is overkill at the perpixel level and will greatly reduce the speed of the code).