Re: [Chimera-users] odd glare when volume rendering

Hi Jeff, Aha! Now I see Chimera is working as expected and I can reproduce the glare on my computer. If you have depth cueing set to "No color", which is the default, *and* you use a light background color, then Chimera interprets "no color" as white. With a dark background color, I use black, "no color" for depth cueing is interpreted as black. So all I had to do was set by background color to a light shade to see the glare. So this is bad behavior. The white depth cue color does not work with volume rendering -- it is way too powerful -- all the far planes in the data become slightly white, and this ends up making a very white brick. Oddly, I have already fixed the problem, accidently! My current development version of Chimera (not on the web) has a new blending mode for volumes. I made the change to address a serious problem you raised earlier that the brightness in volume rendering changes a lot when you change step size. The new mode fixes that and will be the default in the next snapshot. Coincidentally the new blending mode also makes white fog work as expected without an overly powerful effect. I have also added better handling of large EM tomography maps -- file loads report progress and can be canceled, default initial display can show a single z plane, the z plane slider is built into volume viewer, hdf5 format map files can be written which contain subsampled versions of the map allowing rapid display of the data at any scale. I'm testing all this on an 2048^3 map. A snapshot should be out in a month or so, though if you really want bleeding edge stuff I could probably give you an earlier version for mac os. Tom William Jeffrey Triffo wrote:
hello,
I am getting an odd glare when I use solid rendering in VolumeViewer - it is orientation dependent, which makes me think it has to do with lighting? I am using build 2416; is it possible to forward a screenshot to the list?
thanks,

Elaine points out that "no color" for depth cueing really uses the background color, not necessarily black or white as I said in my previous message. The "glare" problem in volume rendering becomes apparent only when the background color has differing non-zero red, green, or blue components! Why? Because volume rendering sums up these color values for planes at many depths, but the sum for each of the RGB components is clamped to a maximum of 1. So with background color, say RGB = (1, 0.5, 0) the sum of the depth cue color on the planes ends up being (1, 1, 0) due to the clamping which is a different color, not matching the background and it looks like a bright brick in the volume rendering. Tom Elaine Meng wrote:
Technically, "No color" makes depth cuing use the same color as the background (not necessarily either black or white), but close enough for the purposes of your discussion!
On Aug 3, 2007, at 12:30 PM, Tom Goddard wrote:
If you have depth cueing set to "No color", which is the default, *and* you use a light background color, then Chimera interprets "no color" as white. With a dark background color, I use black, "no color" for depth cueing is interpreted as black.
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Tom Goddard