Glow+Alpha Extracting question

[chris-giusti]

I have been playing with glows and I can't seem to export my glow as raw data in any file type that has alpha.. It will mask the object but not the glow. The first picture is somewhat what it should look like and how it renders in maya (saved out just as jpg) and the second is what happens if I save it out as a png or tga file and attempt to add any sort of background.

What I'm wondering is if there's a way to extract the raw data with the glow and with alpha - what would I need to change to do this?

[joojaa]

what would I need to change to do this?

Just make the layer mode add, in the pplication you use. That makes it visisble. Then if its not alpha avare on add just put a normal layer of same atop.

But yes you could key it. Or you could render the alpha separately with pure white glow and mate white nonshading objects. But this does not really work right because glow has a different kind of layering mode than solid stuff.

In anycase you should not really use maya glow but rether make the glow of your post application., its much more flexible. And scince your opening the post applcation ANYWAY.

[ngabriel]

Chris, I am facing exactly the same problem as you have above and have just come across your post.

Did you ever come up with a fix for saving out this glow effect in Maya, without the post glow as a work around?

Thanks.

[joojaa]

The reason you find this very hard to do is because of the way photoshop, and a few other notable exception, assumes you want to handle alpha. The problem does not to my knowlege happen in many other applications, this is extremely simple in, shake , fusion, even after effects. But is insanely hard to do with prohotoshop or some other still image editors in general because the load module just destroys the the entire alpha data. You can substitute the photoshop load plugins for formats with older versions, or things like older super png loader this makes your life MUCH easier. on this fornt but makes 90% of all your OTHER work suck. In fact ohotoshop used to work the way you want to back in 2000 or so, which is why its possible to revert back to this behaviour.

So if you use photohsop theres relally no nice way to do this Photoshop destroyed the image on load. Its a age old alpha inetrpretation thing, and in this case there exists 2 differetn camps of tought. Staright or premultiplied, thing is the premultipled makes little sense to photosop users in general terms. But when doing 3d graphics its the natural outcome. Now it just so happens thet premultipled alpha is much used in video stuff and all but heard of in still pictures world*.

Anyway its not very hard as i told you jsut set the mode to add and subtract alpha form channel behimnd and it works. BUT THIS DOES NOT WORK OUT IN PHOTOSHOP** You can work aroud photoshop but not much point in doing that just switch the load module.

without the post glow as a work around?

Glow is post no matter what, so it can never be a workaround to make post glow. I it was then it would be a workaround by definition.

• who try to pretend the problem does not exist.
  ** there are 10 or so very freaking big design mistakes in photoshop that will when you know more about image processing that WILL make you loathe the program.

PS: this all is pretty easy to prove, so you doesn't have to take my word for it. But i have no interest in this proof per see. Anyway try saving file without alpha and one with just alpha fill alpha with black, put the non alpha version on top of the alpha balck layer and put the topmost layer to linear dodge which is basically what photoshop calls add. which is basically 3 clicks in any sane comp app. Hiwever theres a more natural routine for this render scene without glow then form commandline just glow with no alpha and load that layer on top with add mode.

[chris-giusti]

I did find a workaround.. I think I rendered the object out without post effects in one render pass layer (Mental Ray -> Translation -> Uncheck Export Post Effects to disable the glow. Then, on another pass just keep the glow object in it with this post effect exportation still on* and save it as .TIF (optimal as far as space and quality goes without loss of detail), and then just apply those glow layers onto your other passes as Add (thanks to Joojaa for that tidbit of advice).

• As well as masking objects; make them surface shader black just for the one render layer.

So for the case of this sword thing.. the entire sword would be exported without post effects and only the blade itself would have to be on another pass with post effect active, with the hilt masking as surface shader black (Because otherwise the glow will look like it's coming from places it shouldn't be). I made a quick picture to show the results: The glow pass (Top Picture), The Non-Post Effect Pass (Mid Picture), and how Add creates the illusion of alpha, as if the object actually has alpha (Bottom Pic). You must remember though that the object really does not and never will have alpha, and add works only when a background is present, so you can't re-save your images out as if they had transparency or an alpha channel unfortunately.