If I look to the histogram of the textured images I can conlcude that there are only 4 bits to code the colors of the textures.
(I use GL_NEAREST and a textured object over the whole screen - with GL_REPLACE to see thid effect)
How it could be changed?
Here is the code:
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glGenTextures(1,&m_myTexture);
glBindTexture(GL_TEXTURE_2D,m_myTexture);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAP_S,GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAP_T,GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST);
glTexEnvf(GL_TEXTURE_ENV,GL_TEXTURE_ENV_MODE, GL_REPLACE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, columns,rows, 0, GL_RGBA, GL_UNSIGNED_BYTE,
(unsigned char*)checkImage);