Cycles vieport render different from final render

Hi all,

Im scratching my head here.
Please have a look at the screen shot:

I have a tunnel where I have placed neons on. I want to comp this render onto existing footage, so I would like the light reflections to be on an alpha.

On the bottom right, you can see what the material of the tunnel is.
To the left of that, the viewport render shows what I want…so the neons and their reflections show.
To the left of the viewport render is the actual render…neons show up but the reflections on the tunnel are gone.

Please help

It probably is in the render, but the way alpha is handled in the 3d viewport and image viewer is different. In the image viewer, it seems alpha=0 means only checkered background, no matter the color. Try to switch the image viewer (top-right drop-down) from ‘color and alpha’ to ‘color’.

1 Like

Thanks for this.
You’re right, I can see it when I switch from color and alpha to color.

But the problem now is when I bring the render into after effects:
Still looks like the reflections are gone. Only when I apply ‘levels effect’ to the render, and set to only affecting the alpha, then I can get some of the information back, but it has to be such an extreme push to recover that, which ends up looking very grainy and rubbish compared to the neon tubes which stay clean.

Is there a way to boost those reflections over the alpha in cycles rendering itself?

It probably is best done in the compositor. What you likely want is to increase alpha to higher values where the image is non-black. Something like this could work:

Optionally add more converters for tweaking between V and Maximum, e.g. a color ramp.

Or if your image editor can combine layers by ‘adding’, you could split out the reflections into a separate layer without alpha and ‘add’ that layer to the background instead of mixing with alpha mask.

1 Like

You have been a great help!

I was hoping it was something simpler but I will give this a go.