GL Formats:

Note that "1" is defined as 1.0f for UNORM, SNORM, FLOAT formats and 0x1 for UINT, 
SINT formats (see the GL_EXT_texture_integer specification for more information).

GL_LUMINANCE_ALPHA  
{ 
    R = L, 
    G = L, 
    B = L, 
    A = A, 
},

GL_LUMINANCE        
{ 
    R = L, 
    G = L, 
    B = L, 
    A = 1, 
},

GL_INTENSITY        
{ 
    R = I, 
    G = I, 
    B = I, 
    A = I, 
},

GL_ALPHA            
{ 
    R = 0, 
    G = 0, 
    B = 0, 
    A = A, 
},

GL_RED				
{ 
    R = R, 
    G = 0, 
    B = 0, 
    A = 1, 
},

GL_RG				
{ 
    R = R, 
    G = G, 
    B = 0, 
    A = 1 
},

GL_RGB
{
    R = R, 
    G = G, 
    B = B, 
    A = 1, 
},

GL_RGBA
{
    R = R, 
    G = G, 
    B = B, 
    A = A, 
},