Image editor fonctions

[Marc Chaumier]

Hi, Roy, in Image Editor, we can combine 2 different rendered images to obtain a picture accomplished, with the option "arithmetic". But I noticed two option with different results: "Combine" and "Add". Here is my question: Do the "combine" option an average image of the 2 rendered? And so the "add" option add the 2... And so, why in the "add" case, the wire netting disappear?

Thanks.

[Roy Hirshkowitz]

Combine does a weighted average of the two images based on the number of passes of each one.  For example, if one image has run for 200 passes and the next has run for 600 passes they will be weighted by 0.25 and 0.75 repectively.  The result is an image equivalent to an 800 pass run (or pretty close to it.)  It works well for combining runs generated by e1 or e4 (it does not work for e0.)

Add is just straight up pixel addition, no weighted averaging (or averaging of any kind) takes place.  It should not be used in the situation above-- the results in terms of luminance values will be incorrect-- even if the tone-mapped picture looks ok.  It is used for adding together strips generated by the Render Farm when using e0.

Not sure what's up with the wire netting in this case but it probably has something to do with how the alpha is handled.

[Marc Chaumier]

Thanks for your explanations Roy. So in my case (render in several sessions), I will use the combining option.