code:

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/* change colorspace */
Parse Arg Opts
Parse Value Opts with File ' ' RSpace ' ' GSpace ' ' BSpace
Call Open(File,File,R)
If Readch(File,4)~="FORM" Then Exit(0) ; Read$=Readch(File,4)
If Readch(File,4)~="ILBM" Then Exit(0)
Do Forever eof(File) | Chunk="CMAP"
Chunk=ReadCh(File,4)
say Chunk
If eof(File) | Chunk="CMAP" Then Leave
Chunklength=C2D(ReadCh(File,4))
Chunklength = Chunklength + Chunklength // 2
RPos=Seek(File,ChunkLength,Current)
End
CMAPLength=C2D(ReadCh(File,4)) ; CMAPPos=Seek(File,0,Current)
CMAP=ReadCh(File,CMAPLength) ; Cl=Close(File)
TR = 2 ** (8 - RSpace) ; MR = 255 / (2 ** RSpace - 1)
TG = 2 ** (8 - GSpace) ; MG = 255 / (2 ** GSpace - 1)
TB = 2 ** (8 - BSpace) ; MB = 255 / (2 ** BSpace - 1)
Do Dl = 1 To CMAPLength By 3
R=((C2D(SubStr(CMAP,Dl,1)) / TR) % 1) * MR % 1
CMAP=Overlay(D2C(R),CMAP,Dl,1)
G=((C2D(SubStr(CMAP,Dl+1,1)) / TG) % 1) * MG % 1
CMAP=Overlay(D2C(G),CMAP,Dl+1,1)
B=((C2D(SubStr(CMAP,Dl+2,1)) / TB) % 1) * MB % 1
CMAP=Overlay(D2C(B),CMAP,Dl+2,1)
End
Call Open(File,File,A)
WPos=Seek(File,CMAPPos,Begin)
Wr=WriteCh(File,CMAP)
Cl=Close(File)

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