how to show the grey-scale image?

system · September 30, 2003, 6:27am

hi,

sorry for this stupid queation. I just used the function glTexImage2D to show an image:
glTexImage2D(GL_TEXTURE_2D, 0, 3, image->sizeX, image->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, image->data);
It works well with a color image, but when I tried with an intensity(grey-scale) image and changed the components(the 2rd parameter of this function) to 1, just a white block of same size appears on the window. Can anybody give me some suggestion?

Thanks

system · September 30, 2003, 7:09am

sorry, wrong type, should be the 3rd, not 2rd.

Mazy · September 30, 2003, 7:53am

first of all ( im still working on enlighten all people ) the 3rd parameter shoulndt have just ‘3’, it should have an enumrator telling the driver what internal format you want ( GL_RGB(A)4 for 16bit, GL_RGB(A)8 for 24/32 bit, or just GL_RGB(A) if you dont care.

for the rest of the question, format should be GL_LUMINANCE, and internalfomrat (3rd parameter) should be one of GL_INTENSITY, GL_INTENSITY4, GL_INTENSITY8, depending on selected quality

system · September 30, 2003, 8:20am

Thank you for your reply.

Do you mean like this:
glTexImage2D(GL_TEXTURE_2D, 0, 3, image->sizeX, image->sizeY, 0, GL_LUMINANCE, GL_INTENSITY, image->data);

But it doesn’t work.

Mazy · September 30, 2003, 9:08am

you sttill use bytes dont you?
and what did i say about the 3rd parameter (grrr)!!

glTexImage2D(GL_TEXTURE_2D, 0, GL_INTENSITY8, image->sizeX, image->sizeY, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, image->data);

system · September 30, 2003, 10:06am

I’m sorry for misunderstanding. But it still doesn’t work.

Mazy · September 30, 2003, 11:13am

do you get any errors ? ( glGetError )

Jan · September 30, 2003, 12:37pm

If you still use your colored (that means 3 channel RGB texture) but want OpenGL to make a greyscale texture out of it, then you have to do it this way:

glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, image->sizeX, image->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, image->data);

The 7th parameter tells OpenGL how YOU have the data at hand (in this case you have a 3 component image, consisting of red, green and blue) and the 3rd parameter tells OpenGL how IT is supposed to store it (int this case as a greyscale texture).

Mazy has mixed the 3rd and 7th parameter accidantly around.

You should get a good book or some other documentation about OpenGL. Such problems can easily be solved by simply looking up a description of the function.

Jan.