Blender: Change Cycles render seed automatically

Here is a small Blender add-on to change the seed value for the Cycles render engine automatically before rendering a frame.

The seed value determines the noise pattern of a cycles render.

If you only render one image, this is of no concern for you.

If you render an animation, you get the same pattern for each frame which is very obvious for the viewer.

To counter this, you can enter #frame as seed value (creating a so called driver) which returns the frame number as seed value. This gives you a different noise pattern per frame which makes it look like film grain.

This obviously only works if you have an animation to render, but not with a single frame.

After installing the add-on you see an additional checkbox in the render samplig panel where you can switch this feature on or off.



Why to go the trouble to write an add-on for this?

Lately I have used image stacking a lot.

This technique allows you to reduce noise in pictures created by Cycles rendering engine by rendering the same frame multiple times - provided you change the render seed. You then can calculate the "average" of these pictures (e.g. using ImageMagick) cancelling out some noise.

If you want to a clearer version of an image that has just rendered over an hour, you save it and render it again, then stack the images. This is much faster than scrapping the first image and re-rendering it with a larger sample count.

After forgetting to change the seed value a couple of times, the level of suffering was high enough to make an add-on. :-)