glDrawPixels in grayscale?

tags:

c++
opengl

views:

291

answers:

+1 Q:

glDrawPixels in grayscale?

+2 A:

A perverse idea for you to try, and I've no idea if it'll work:

glPixelZoom(1.0f/3.0f,1.0f);
glDrawPixels(3*width,height,GL_LUMINANCE,GL_UNSIGNED_BYTE,data);

ie treat your 3-channel image as being a 1-channel (grayscale) image 3 times as wide, and compensate for this by squishing the width using the x zoom factor. I believe GL always does nearest-neighbour sampling for zoomed glDrawPixels, so it ought to consistently pick out the same component from each triple of samples, as you require.

timday 2009-04-14 12:10:10

Oh my God..... I can't believe that works! It sort of splits the image in half, and one side grainier than the other, but it works.

Mark 2009-04-14 19:52:28

Could be something to do with the precision with which 1.0/3.0 is maintained internally (especially if it works OK up to a certain size). I'd suggest adjusting the ratio very slightly or using a 4-bytes-per-pixel format and a zoom factor of 0.25.

timday 2009-04-14 21:49:14