Message-Id: <3.0.6.32.19990211183010.007ca480@pop.netaddress.com>
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Date: Thu, 11 Feb 1999 18:30:10 -0500
To: djgpp AT delorie DOT com
From: Paul Derbyshire <pderbysh AT usa DOT net>
Subject: Re: Help: Converting 24bit bitmap to seperate R,G,B files
  using Allegro?
In-Reply-To: <35FE2CA2.5E93@ns.sympatico.ca>
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Reply-To: djgpp AT delorie DOT com

It must be just sending the color components separately. You need to split
your 24 bit color bitmap into three 8 bit bitmaps where the pixel color
number in the 8 bit bitmaps is one component for the 24 bit bitmap. Like
this...

(Disclaimer: Untested, quick and dirty, and no error checking. Assumes the
24 bit bitmap is in bbggrr pixel format also. And not very optimized!)

typedef struct {
  BITMAP *r; // These should be 8 bit.
  BITMAP *g;
  BITMAP *b;
} split;

split split_image (BITMAP *bmp) {
  // Arg should be 24-bit.
  split sp;
  int x, y;
  unsigned int c;
  sp.r = create_bitmap_ex(bmp->w,bmp->h,8);
  sp.g = create_bitmap_ex(bmp->w,bmp->h,8);
  sp.b = create_bitmap_ex(bmp->w,bmp->h,8);
  for (x=0; x<bmp->w; ++x) {
    for (y=0; y<bmp->h; ++y) {
      c=getpixel(bmp,x,y);
      putpixel(sp.r,x,y,c&0xff);
      putpixel(sp.g,x,y,c&0xff00);
      putpixel(sp.b,x,y,c&0xff0000);
    }
  }
  return sp;
}


Send sp.r, sp.g, and sp.b to the printer in the correct order, then
remember to destroy_bitmap() all three.

-- 
   .*.  "Clouds are not spheres, mountains are not cones, coastlines are not
-()  <  circles, and bark is not smooth, nor does lightning travel in a
   `*'  straight line."    -------------------------------------------------
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_____________________ ____|________     Paul Derbyshire     pderbysh AT usa DOT net
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