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    Post processing errors

    I just started experimenting with UDK again, and I'm noticing some artifacts in my render. I just did a clean installation of the November UDK with a blank project, and so far all I've done is set up a post processing chain and created an experimental shader. The shader converts the output to look like terminal ASCII art. I'll go ahead and explain the artifacts I'm getting with images.



    In this first image, you can see along the top and down the left a 1 pixel wide artifact. It looks as though the original image is leaking through here. You can maybe see it better in the zoomed section.



    This one is not visually noticeable, but I picked up on it in Photoshop. I manipulated the image to bring out in red the areas where there is some deviation. Basically the areas in red have one or more of their color component off by a value of 1 or maybe 2. It's sort of a splotchy pattern that seems to form around edges.



    This is the texture which stores my bitmaped fonts. I'm basically just sampling the Scene Texture, and using the luminance value to index into this texture the appropriate ASCII character and sampling to display on the screen. The font texture only contains 100% black and 100% white pixels, and everything is 1:1, so the output image should also contain only 100% black and 100% white pixels. I have no idea what is causing these "splotches".

    I don't think that my shader code is very relevant so I'm not going to bother uploading diagrams and code. Other than enabling my post processing chain under world setting, I have not done anything else to this project.

    #2
    Just to prove it's not anything in my material that's accounting for this.

    Here are the results of setting up a post process chain with nothing but a single material node.

    In that material I have nothing but a single Custom node connected to the emissive channel.

    The HLSL is just "return float3(0, 0, 0);"

    And here are my results.


    http://s20.postimage.org/h6nekk2i5/example3.png

    This is 1280x720 contents of the window. Should be just a solid black screen. But it's not!

    You should be able to plainly see that there is a 1 pixel wide border along the top and left. You should be able to tell that what is happening here is that the post process effect is not being applied to this part of the screen at all.

    Next, you should be able to assume that every pixel in this image will be pure black (rgb [0, 0, 0]). Nope!


    http://s20.postimage.org/92faftg31/example4.png

    This image has had it's contrast adjusted in Photoshop to emphasize the random (imo smudgy looking) artifacts around the screen. In reality the largest error is a pixel value of rgb [4, 4, 4], which isn't perceptible to the eye, but it's still a long way off from [0, 0, 0]!

    Seriously UDK, what gives?

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