id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	blockedby	blocking	notify_on_close	platform	project
1761	Volume rendering artifacts from 8-bit colors	Tom Goddard	Tom Goddard	"Volume rendering as a 3d image sometimes appears darker at step 1 compared to step 2, or has dramatically different brightness when using z-axis planes versus x or y-axis planes.  These variations in appearance can be caused by using 8-bit colors in OpenGL framebuffers and textures with many (e.g. np > 100) highly transparent planes (e.g. alpha < 5/255).  The variable brightness comes from limited resolution especially in texture transparency values, for example, with 8-bit alpha ranging from 0 to 255, 100 planes of alpha = 1 gives very different appearance than alpha = 2.  Likewise accumulating in the frame buffer the sum of 100 planes with 8-bit red value = 1 is dramatically different than red value = 2.

Cases of incorrect appearance are common when rendering volumes with grid size > 100.  For correct appearance the range of color and alpha values (256 values for 8-bit) needs to be substantially greater than the number of planes.

I tested using 16-bit rgba in the framebuffer and textures and this gave accurate consistent coloring.

It would be useful to allow the user to render with 16-bit rgba.  It probably should not be the default since it is likely to reduce rendering speed.  Both graphics and volume code would need improvement to enable 16-bit RGBA.
"	enhancement	assigned	moderate		Volume Data								all	ChimeraX