   correlation between texture access in a shader and internal format of a texture
  I am wondering about the following:if i create a texture like this for example:glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, width, height, 0, GL_ALPHA, GL_FLOAT, buffer);then the texture data only holds alpha components. But when I acces a texture in a shader with texture2D() I always get a vec4, means I have also RGB components. Obviously the shader can't get them out of the texture (only the alpha is provided there) so how is the specification of the result of texture2D() for components, that are not provided by the texture?   
  Table 3.21 on page 184 in the OpenGL 2.0 specification describes how the full 4-component color vector is constructed from different texture formats. I assume that table is valid for GLSL aswell.   ;  thanks!!!thats exactly what i needed. :-) I also think the same applies to GLSL   