Blurred Design

Week 4

Well, its week four and here we are, this is where the difficulty ensues. Well, at least for me. This week we started to learn about blurring.

Convolution Kernel Filtering

Kernel filtering is a way of processing images through a “filter”. Through it you take a sample of the pixel and the surrounding pixels from its texture, then you use the sum of these pixels based on their weight. This new pixel is placed on to a new texture.

When you need to move over pixels you increase you pull location by 1/textureWidth and when you reach the end of a row you need to increase the height by 1/textureHeight.

More information: http://www.aforgenet.com/framework/features/convolution_filters.html

Blurring

Box Filter – A filter\ where every pixel is weighted the same.

 Left- regular image, Right – Box Blurred

Gaussian Blurring - Where the middle has a higher weight and the surrounding ones have a lower weighting; the bigger the sample window, the stronger the blur.

Edge Detection

Design a convolution kernel that favours things with a high change. Output values where left right values are different. For example the following is a sobel filter.

-1	0	1
-2	0	2
-1	0	2

-1	-2	-1
0	0	0
1	2	2

The top graph detects for edges on the x axis while the bottom graph detects for edges on the y axis. This gathers data for when the color of an object drastically changes letting us find when there is an edge. Then at this edge we can add in extra light. Normally you would do this in the lighting and shading but you do not have access to your neighbors in a fragment or vertex shader, therefore you need to do this in a second pass after the whole scene is saved as an image.

HDR, Bloom and Frame Processing

HDR and bloom are done though a post processing effect. It is done after you have your geometry and lighting.

Following the above steps you should end up with three separate textures which you merge together into the final frame. This data is processed in layers where you start with the base image and add the data together into a new image. This is done after rendering. To display your final image you would save everything in you back buffer, then make it into a texture. Then you make a quad the size of the screen and attach this texture to it. Through this process you can do everything through shaders. By sending the vertex information you can interpolate the UVs of the quad and send them to a pixel shader; this shader is called for every pixel. This means that this whole process can go into one function. If we want to make the image smaller than we just need to draw it at a percentage of its size.