Multiply final image by Ambient Occlusion pass = greyscale?

Multiplying my final image by an AO pass results in a greyscale image…is this the expected behaviour? If not, what is the best way to composit in an AO pass?



can you post a screenshot of your node network? are you using the colour mix node for multiplying?

I have kept playing with this and I am closer but still not sure if I what I have makes sense.

I found this post by Bartek and have currently set up my nodes this way:

…but something is not right. I had combined all the render passes correctly as per the instructions in the manual, but when trying to get AO included using the above method…something isn’t working. I have used a math node to multiply my AO pass by a factor, and then used the result of that in the equation by Bartek above. The problem is that the multiply node doesn’t seem to have any effect, so something is not quite right. IT seems to be removing glossy highlights instead…it makes no sense.

The four hidden nodes on the left (plus the top hidden node on the right) are just switches to organise the noodles. The three remaining hidden nodes on the right are mix nodes (I tried them with math nodes…getting confused now!). The mix node on the left has the AO pass as the input:

When I’m looking at your setup - everything seems to be fine. Check if you use proper blend types - here it’s easy to make mistakes.
When multiplying AO by factor - I’d rather use Mix node and set the second color’s all channels to factor value.

I just noticed that you want to multiply FINAL image by AO… Do you really want to? It shouldn’t be done.

Thanks Bartek, I opted against multiplying the final image by AO - I was interested in something that I didn’t fully understand. I realised that made no sense when I saw your post on how to composit an AO pass, so I tried to implement your method there.

What I was aiming for was to simply accentuate the crevices on one sculpted object in my scene. I think I will do it with a dirty vertex shader instead (I have successfully applied that on sculpts before…so I think that is the best way for now). I will likely revisit AO at a later date and see if I can get something useful from it.


if you can post your full node network with nodes not minimized that would also help us figure out what is going on… all i see in your current screenshot is a bunch of nodes that may or may not be doing something which are all minimized.

Sorry, I was on my tiny laptop and I didn’t know how to get a screenshot that wouldn’t be impossible to make out due to small size. I attempted to describe the nodes in lieu of an acceptable screenshot. I will try to get a readable pic when I get home.


Just an idea but you maybe have used the “Math” node to multiply the AO instead of using the “Mix” node.

The Mix node uses a RGB image as channel (yellow colored input) and apply the multiplication on each channel. if you plug a RGB image to a Math node (which uses only one single channel), the result will be a grayscale image.

What’s wrong with preparing a .blend file and uploading that instead?

This can be fixed by separating the RGB channels, multiplying each with the AO pass, then recombine the RGB channels. Not sure if it is supposed to work this way or not, but this is what I did.

[Edit] Yeah, the mix node would probably be more what you want. I also goofed and used math nodes instead. :stuck_out_tongue: