Ok, here's a better version with the alphas {0, 1, 2, 4, 8, 16, 32, 64,
128, 255} for the same rgb values {64, 128, 192}.~> ./catpx pixel10x1.png 0 0 0 0 0 0 0 1 0 127 127 2 63 127 191 4 63 127 191 8 63 127 191 16 63 127 191 32 63 127 191 64 63 127 191 128 64 128 192 255 There seems to be some pre-multiplication as long as alpha != 0. But every single value should actually be "64 128 192 alpha". Best.
#include <osgDB/ReadFile>
#include <osg/ref_ptr>
#include <iostream>
#include <cassert>
typedef unsigned char byte;
struct Pixel {
byte c0;
byte c1;
byte c2;
byte alpha;
};
typedef osg::ref_ptr<osg::Image> ImagePtr;
int main(int n, char** c) {
if(n == 1) {
std::cout << "Usage: " << c[0] << " image.png" << std::endl;
return 0;
}
const ImagePtr img(osgDB::readImageFile(c[1]));
if(img == 0) {
std::cout << "Failed to load: " << c[1] << std::endl;
return 1;
}
const GLenum pxf(img->getPixelFormat());
if(not (pxf == GL_RGBA or pxf == GL_BGRA)) {
std::cout << "Image must be RGBA or BGRA, found: "
<< pxf << std::endl;
return 1;
}
const Pixel* px(reinterpret_cast<const Pixel*>(img->data()));
const unsigned N(img->s() * img->t());
for(unsigned i(0); i != N; ++i, ++px)
std::cout << unsigned(px->c0) << ' '
<< unsigned(px->c1) << ' '
<< unsigned(px->c2) << ' '
<< unsigned(px->alpha) << std::endl;
return 0;
}
<<attachment: pixel10x1.png>>
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