monochrome sequence display

I have 2 questions,

I would like to create a monochrome display
the image.c example is for color (RGB) only
(glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB)).
How to modify it for grayscale/monochrome 8bit ?

2.I would like to realize an sequence viewer.
I’m using the lut lib. How to do repost (or someting else) when send to OpenGL the new computed image when this one is ready (processing time is about 50-80 ms). If I do an infinite loop (associated to a button) which is stupid, I can’t, of course, click the other button to tune the sequence display.
What is the basic mecanism in OpenGL to do so ?

Thanks in advances