Reducing Bitmap Blurring To Get Cleaner
Results By Neil Blevins Created On: Nov 21st 2013
Sometimes you'll have a model that has a texture map on it
and when you get at a glancing angle, the texture map gets super
blurry...
Sometimes changing the bitmap filtering from Pyramidal to Summed Area
helps, but when it doesn't, one other solution is to reduce the bitmap
blur from the default of 1.0 to a small number like 0.1-0.2, or turn it
off
entirely. Or another things to try is turn down the bitmap blur to 0.1
and then increase the blur offset to a really low value like 0.005
(thanks Aaron for the suggestion).
For the image below, I turned Blur down from 1.0 to 0.4 and rendered in
vray.
What's happening is this. All renders do some form of filtering. This
filtering can happen at the bitmap level, or to the entire image, or
both.
Below is a high contrast image, a black dot on a white background. When
you filter it, you get a "blurrier" image, where it averages out the
colors creating grey around the black dot. Filtering even further (or
using a larger filter) gives
you an even blurrier image.
So turning down the blur in your bitmap will frequently give you a much
crisper
result (closer to your original image). There are a number of
considerations though before you decide
to turn down filtering on all your bitmaps.
Advantages of turning blur off:
Crisper textures
Can speed up rendertimes since its not doing the extra filtering
work
In raytracers like Vray, displacement maps and refraction /
opacity maps will render much faster.
Disadvantages of turning blur off:
Some high contrast textures, especially bump maps, can look too
sharp. Or they sparkle, flicker or alias when you move your camera in
animation. In which case, it may be worth increasing the blur to 0.5.
Raytraced renderers tend to do a better job of image filtering
than say the 3dsmax scanline renderer, so if you're using the scanline
renderer, you'll probably want to turn down your blur less, or enable
super sampling on your material (see image below on what will happen if
you turn blur down too far). Personally I'd recommend using a raytrace
renderer
like vray instead, since its image filtering can produce crisper
results without looking as aliased.
If you're using a lot of mipmaps, turning filtering off will
dramatically increase RAM usage (since the images weren't being
blurred, the renderer was choosing a larger mipmap level than it would
normally choose, and hence had way more texture data in memory).
HDRI images can sometimes have unwanted bright spots (areas of
super high contrast) that blurring slightly will fix. So turning off
the filtering will reveal these problems.
So there isn't a perfect one fits all solution, but try turning blur
down or off the next time you see problems and find that good middle
ground between too blurry and too crisp.
