alpha channel
mcorr
Posts: 1,104
I'd like to do some postwork/masking in photoshop. Is there a way to save a render with an alpha channel, or a render itself as an alpha channel?
Post edited by mcorr on
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From what? Daz Studio will embed an alpha channel in tiff or png files, for areas that have no geometry and as long as there was no drawn dome (Render Settings in Iray) or backdrop (Environment pane).
Thanks Richard! I've saved renders in png format and have been able to use them for masking, but ... I've also used alphas in jpegs and it seemed to me that they are more detailed for masking, because I've gotten good results with them, whereas png's haven't always provided me with the ability to knock out all the unneeded pixels.
I'm not aware that jogs support alpha channels. The PNG or Tiff file should have an exact, lossless, version of the alpha so even if jpgs do support alphas in some cases I'm not sure how a lossy format could give better results.
I take your point ... jpegs are lossy. They shouldn't be generating superior masks .... I'll have to run some tests to see where I got that idea from.
I could have sworn that my VUE renders are jpegs with alpha channels ... but maybe they are tiffs or even photoshop files. Gotta check that out. Whatever they are, the masks are very, very good. They knock out almost all of the edge that becomes a problem when compositing. Maybe it's a technique problem on my part, but I haven't been able to duplicate the same level of masking in DAZ. Maybe I just need to render a larger size pict.
It's possible Daz or Ve is handling the alpha data differently if you issue is png related. png supports more than one method for doing that.
I dunno. Stdio generated alpha seem pretty clear to me. Of course, I don't use it that much.
JPG's don't have alpha. The PNG alpha channel from DAZ are perfect according to the render. If it's not working correctly, it's possible the app is not interpreting the alpha channel correctly. There are two types of alpha. Associated and unassociated alpha. In programmer speak, this would be premultiplied and non-premultiplied alpha. Using one as the other gives drastically different results, especially around and on edges.
There seem to be lossy PNGs also. At least you can save a PNG in IrfanView in different qualities.
You can get a smaller PNG as a processing time penalty, but it won't be that much smaller. The compression level option allows you to specify how compressed you want the file to be. Of course, the processing time penalty applies to both ends, writing and reading the file.
Whoever finalized the png spec decided that it was worth while to allow the user to change that setting, but it doesn't introduce loss. You can get lossy artificats out of the way the program handles the image before it creates a PNG. At least wikipedia says so. Some will reduce the the color depth in a lossy fashion to get better compression. Maybe Irfanview does that. I stopped using it for image processing beyond resizing for web stuff (non-transparent only) because irfanview was murdering the alpha.