Re: Converting a 24-bit bitmap (with 256 unique colors) to an 8-bit
bitmap without changing the colors???
On Mar 4, 1:09 pm, "Peter Olcott" <NoS...@OCR4Screen.com> wrote:
Do you think that it could copy from 32-bit to 8-bit
indexed?
I think so. Below is an example.
With some thinking, you might be able to figure out a way to work
directly with the pixel bits (via CImage::GetBits) that can do things
faster.
#include "stdafx.h"
#include <atlimage.h>
#include <set>
int main()
{
// Load the source image:
CImage img24;
img24.Load("256colors.bmp");
// Gather all the colors in the image:
std::set<COLORREF> colors;
for(int i=0; i<img24.GetHeight(); ++i)
{
for(int j=0; j<img24.GetWidth(); ++j)
{
colors.insert(img24.GetPixel(j,i));
}
}
// Make a color table holding the colors:
RGBQUAD table[256];
std::set<COLORREF>::const_iterator color = colors.begin();
for(int index=0; index<256; ++index)
{
table[index].rgbBlue = GetBValue(*color);
table[index].rgbGreen = GetGValue(*color);
table[index].rgbRed = GetRValue(*color);
table[index].rgbReserved = 0;
++color;
}
// Make the destination image:
CImage img8;
img8.Create(img24.GetWidth(), img24.GetHeight(), 8);
img8.SetColorTable(0, 256, table);
// Copy the pixels:
HDC const hdc = img8.GetDC();
img24.BitBlt(hdc, 0, 0);
img8.ReleaseDC();
img8.Save("8bpp.bmp");
return 0;
}