All posts relating to Maxwell Render 1.x
#279781
So I've rendered with an alpha channel (sky comes out black).

Now I want to use Gimp to add a background image. I've been through the Gimp tutorials and I'm going nowhere fast.

Can anyone show me a tutorial that specifically outlines how to use Gimp to add a background image that looks acceptable (not like garbage)?

This is week 3 of trying to add an acceptable background image to my renderings, I've got clients breathing down my neck and am making no money while I fiddle with this stuff. I'm very disappointed that Maxwell Studio doesn't have an intuitive means to apply background images. Yes, I've upgraded to 1.7.1 (as 1.6 was overriding sky channels that were not disabled with a physical sky). Now I've bought dosch skies only to find that, though the hdr image may have a nice blue sky color, the sky color becomes washed out in the rendering. I try to adjust intensity, ozone etc. and nothing comes out looking even 50% realistic.

On the verge of just going over to Cinema 4-D with all this time and money that I'm wasting.

-Jeremy
User avatar
By Bubbaloo
#279789
I'm sorry, I can't help with Gimp, but in Photoshop you take your main image layer (the render) and add a masking layer to it. Then you paste your alpha image into the mask slot and it creates transparency based on the white parts of the alpha image. Then add another layer and place your sky there and it will show through. I don't know if Gimp works anything like PS...
On the verge of just going over to Cinema 4-D
Maybe that's not a bad idea. I practiced with Maxwell for a month while still using mental ray for production. I don't think I would recommend jumping into a new software head first with deadlines looming.

Good luck to you!
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By Mihai
#279798
Do you have a good 2D image of a sky you would like to add as a background? That's really the most time consuming part.

The procedure is you render also an alpha channel from Maxwell (check both render and alpha channels in Studio).

Open the render and the alpha channel (they are two separate files)

Now I'm not sure how Gimp does it but it's the same procedure in any image editor: Copy the alpha image into the render image (into the Channels tab/palette or whatever it is in Gimp so you get a new alpha channel).

Make a selection of this alpha channel (in Photoshop you Ctrl click on the alpha in the Channels palette

Switch from the Channels tab to the RGB tab, and using the selection you made earlier, copy>paste so you get a new layer with only your building in it and the rest cut out.

Now just add in your image of a sky in another layer beneath this one and that's it.
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By Rickyx
#279810
Translated in Gimpish:

Open the render
Drag the alpha render in the layer box and select it.
Right click "Add layer mask" pick "copy of the layer in grayscale" or similar.
Right click again and choose apply layer mask.

You got the mask.

You can have the proper (inverted selection) by right click "get mask from selection" and ctrl+i as you have to invert the mask.

You have got the selection.

Select and duplicate the render layer.
Canc to erase the alpha.
Erase the background layer and the alpha.

Voilà

I'm sure is more complicated to explain that to do it...!
User avatar
By Rickyx
#335517
Edited 2 years later...
Translated in Gimpish (8 bit retouching):

Render with the embedded option and a format with multi-page like tiff.
Open all the layer embedded (render and alpha).
... like before ;)
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Thanks Luis, it's great to see progress with MW!

Thanks Fernando!