View Full Version : comping smoke, transp issues
12 December 2008, 08:31 AM
I was wondering what the best way to comp in smoke elements. I have smoke renders from Maya that look great and have an aloha channel. When I try to comp it into the rest of the scene, also created in Maya, it is way to transparent. Even with over nodes. I have tried expanding the alpha and laying down black first. That helped. I also tried crushing the alpha (so the alpha would fill in more). The more I layer it, the more it turns out muddy grey.
12 December 2008, 11:24 PM
well 3d smoke always looks good over black because of the contrast. When you are making the 3d element what are you using as reference for the lighting ? if you are trying to add thick CG smoke you need to be prepared to do a lot of subtle colour corrections in order to make it sell. Also you will never get the smoke to look identical on live action than it does on black.
It really depends on the type of smoke you are trying to emulate but I tend to use compress and gamma to control the highlights and B/W points of my smoke individually when compositing. Another thing to do is to double the smoke over itself and colour correct each element before layering them down at an opacity less than 1.
basically you are trying to emulate volumetrics.
Have you got some examples of what you are trying to achieve.
12 December 2008, 12:39 AM
How is the alpha?
I am guessting it looks more or less like one of the rgb channles. If thatīs the case you can always use an expand node and play with the alpha slider to make it less transparent
12 December 2008, 10:30 PM
I have attached the smoke images (http://s427.photobucket.com/albums/pp359/pixlmonky/). Sorry about the jpegs. The project is still NDA, so i can not post the other plates. The question was more about the transparency. I tried layering black down as a base to layer the white smoke over. Then layerd the white smoke over twice and also compressed and iAdded it. It is still barely visible. I can't expand the smoke too much or I start getting harsh smoke edges. Looks great over black. Not so great over lighter background plates. This will be comp'd over something resembling a mid-day desert. I am looking for a light smoldering look and also a darker billowing look (two different shots). I am thinking I may need to make the smoke denser in the Maya render.
Thanks for the replies
12 December 2008, 05:02 AM
Try to blur the BG behind the smoke using the alpha of the smoke and then comp the smoke on top of it. This should do the trick to sell it as "more dense". You could adjust the gamma of the smoke's alpha before you pipe it in the blur to control the amount of blurring.
12 December 2008, 05:17 AM
Thanks for the suggestions. I'll give them a go when I get back to the office after the holidays. I figured it would take a lot of layering to peprep the smoke.
12 December 2008, 06:02 AM
Another thing you might try is taking the matte of the smoke and pushing solid colour through it. take a look at some of the shots in the 'recent' work section of my website, I have just come off a show with a lot of complex smoke and pyro integration. It really isn't hard once you get started. I recommend taking a look at good reference material and trying to come to grips with the way smoke reacts to various light conditions.
good luck .
12 December 2008, 06:02 AM
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