# blurring a face

Hi erverybody

Unfortunately i have some problems with https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch14.html

In chapter 14.4.7 there are the figures 14-13 and 14-14. Figure 14-13 defines some parameters for a 6-gaussian-filter. Figure 14-14 shows the result.

My first question: „variance“ in figure 14-13 is defined in mm^2. Is this the area of a square, a circle or something different??

My second question: A texture consists of texels, a texel has a certain size. How large must a texel be, so that i can use the parameters in figure 14-13? If a texel is too large, a face is blurred too strong. If a texel is too small, a face is hardly blurred. So the face must have a certain size and a texel must have a certain size. But how can i calculate these sizes?

Fig. 14.14 defines “radial distance (mm)” so it seems evident that “mm^2” is this distance (presumably in millimeters) squared; comparing squared distances is a common optimization trick in graphics as it helps to avoid having to compute square roots at runtime. It’s worthwhile you reviewing the article for other references to “radial” or “distance” which may help provide further context. As for how large a textel should be, while I’m not familiar with the specifics of the article, this is obviously something that you can tune yourself. As you mention, you select a texel size depending on the blurring intensity you want, and experiment with different sizes until you find one that looks good to you.