I am working to get an image of an emissive plane(unlit) using a orthographic camera. But I found that left and right sides of output image will become darker due to some unknown effects. It looks like a dark corner effect(but up and bottom sides are normal). Then I tried to render a white emissive plane, I deleted all the light sources and got a picture below:
Although the material is unlit, it still seems to be affected by some light. I am so confused.
Thanks in advanced!