Strange color shift after loading a GL_RGB texture

Question

Here's a primitive 5x2 texture, defined in RGB and RGBA formats.

//                       1               2               3                     4               5
unsigned char rgb[]  = { 0, 0, 0,        0, 0, 0,        200, 200, 200,        0, 0, 0,        200, 200, 200,
                         0, 0, 0,        0, 0, 0,        200, 200, 200,        0, 0, 0,        200, 200, 200,       };
unsigned char rgba[] = { 0, 0, 0, 255,   0, 0, 0, 255,   200, 200, 200, 255,   0, 0, 0, 255,   200, 200, 200, 255,
                         0, 0, 0, 255,   0, 0, 0, 255,   200, 200, 200, 255,   0, 0, 0, 255,   200, 200, 200, 255,  };

Loading the RGBA version works as expected:

glTexImage2D(GL_TEXTURE_2D,
             0,       // mipmap level
             GL_RGB,  // dest format
             5,       // width
             2,       // height
             0,       // deprecated
             GL_RGBA, // source format
             GL_UNSIGNED_BYTE,
             rgba);

Loading the RGB texture results in a weird color shift:

glTexImage2D(GL_TEXTURE_2D,
             0,       // mipmap level
             GL_RGB,  // dest format
             5,       // width
             2,       // height
             0,       // deprecated
             GL_RGB,  // source format
             GL_UNSIGNED_BYTE,
             rgb);

The difference in the code between the first and the second screenshot are just those two arguments to glTexImage2D.

What am I doing wrong?

Environment

• ATI Radeon HD5450, OpenGL 4.2
• Windows 7, 64-Bit
• Visual Studio 2010

Chauvin

Did you set the pack alignment? Default is 4 bytes, so the rgba array will be OK, but it won't work with the rgb array. – Gob

No. What arguments to glPixelStorei would fix this issue? – Chauvin

See here -- glPixelStorei(GL_UNPACK_ALIGNMENT, 1) should fix it. – Gob

Thanks so much! Add an official answer, if you like. I'll gladly vote you up. – Chauvin

Answer 1

See here -- glPixelStorei(GL_UNPACK_ALIGNMENT, 1) should fix it.

Gob