Simon Wicker
09-11-2005, 04:37 AM
Hi all,
Dann Stubbs mentioned that I once posted a 'how to' on adding film grain to a render in that 'other thread'. I thought I'd pass it on again in case anyone is interested as the original has, I'm sure, disappeared into the mists of the past.
Most compositing apps have an add grain button now that attempts to analyze the grain in a piece of live action and then you can apply that grain to your renders (i.e. after effects, combustion and shake) but there is no harm in knowing the manual way of doing it.
I'll talk about Photoshop but the technique is usable in most apps. The first thing to do is to get yourselves a piece of footage from a real camera that you are matching to. In the visual effects world this would be the live action plate that your render would be dropped into, but even if you are just doing a still and would like to make it look more photorealistic it is still a very good idea to try and track down a real photographic image that matches your shot (so you have something physically accurate to match to). Have a look in Photoshop at how the grain in this real image is distributed. The best way to do this is to check each of the RGB channels individually in the channel palette. All of the channels will have a different distribution of grain, amount, size, etc. The blue channel is generally the most grainy, red and green the least grainy. There will also be a change in the granularity of the highlights, midtones and shadows. Keep this image handy as reference and open up your cinema render.
In photoshop create a new layer above your render, fill it with 50% grey and call it something obvious like 'Grain'. Change the blend mode of your grain layer to HardLight. HardLight mode is great because they grey will become transparent but any noise that you add to this layer will either be screened or multiplied with the render layer below depending on its brightness so you can experiment non-destuctively with what looks best. Now with the grain layer still selected go to the channels palette and then individually (and with reference to the degree of grain present in your live action plate) use the add noise filter to affect each of the RGB channels separately - you will click on each channel one at a time to make it active and then run add noise on just that channel. You can also blur each channel separately (often the blue channel is grain is very clumpy so you may need to blur this channel and then adjust the levels to bring the contrast back). Once you have matched each of the RGB channels individually you can then copy your base render and paste that into a layer mask attached to the grain layer. Adjusting the levels on this layer mask will tweak how much of the grain appears in the shadows, midtones and highlights (although obviously to supress the grain in the highlights you should invert the colour of the layer mask).
Hopefully that will be enough to get people started, I'm sure there are other recipes. Other things to remember when comping a render over liveaction or other photographic plate are things like edge blur (where you may need to run an edge detect on your alpha channel and use that to subtly blur the edges of your render into the background), adding light wrap from the background so that strong lights in the bg bleed into your foreground cg, and adding bloom to the brighter parts of your cg so that it mimics the halation you get when film and CCD records an overexposed image.
Cheers, Simon W.
Dann Stubbs mentioned that I once posted a 'how to' on adding film grain to a render in that 'other thread'. I thought I'd pass it on again in case anyone is interested as the original has, I'm sure, disappeared into the mists of the past.
Most compositing apps have an add grain button now that attempts to analyze the grain in a piece of live action and then you can apply that grain to your renders (i.e. after effects, combustion and shake) but there is no harm in knowing the manual way of doing it.
I'll talk about Photoshop but the technique is usable in most apps. The first thing to do is to get yourselves a piece of footage from a real camera that you are matching to. In the visual effects world this would be the live action plate that your render would be dropped into, but even if you are just doing a still and would like to make it look more photorealistic it is still a very good idea to try and track down a real photographic image that matches your shot (so you have something physically accurate to match to). Have a look in Photoshop at how the grain in this real image is distributed. The best way to do this is to check each of the RGB channels individually in the channel palette. All of the channels will have a different distribution of grain, amount, size, etc. The blue channel is generally the most grainy, red and green the least grainy. There will also be a change in the granularity of the highlights, midtones and shadows. Keep this image handy as reference and open up your cinema render.
In photoshop create a new layer above your render, fill it with 50% grey and call it something obvious like 'Grain'. Change the blend mode of your grain layer to HardLight. HardLight mode is great because they grey will become transparent but any noise that you add to this layer will either be screened or multiplied with the render layer below depending on its brightness so you can experiment non-destuctively with what looks best. Now with the grain layer still selected go to the channels palette and then individually (and with reference to the degree of grain present in your live action plate) use the add noise filter to affect each of the RGB channels separately - you will click on each channel one at a time to make it active and then run add noise on just that channel. You can also blur each channel separately (often the blue channel is grain is very clumpy so you may need to blur this channel and then adjust the levels to bring the contrast back). Once you have matched each of the RGB channels individually you can then copy your base render and paste that into a layer mask attached to the grain layer. Adjusting the levels on this layer mask will tweak how much of the grain appears in the shadows, midtones and highlights (although obviously to supress the grain in the highlights you should invert the colour of the layer mask).
Hopefully that will be enough to get people started, I'm sure there are other recipes. Other things to remember when comping a render over liveaction or other photographic plate are things like edge blur (where you may need to run an edge detect on your alpha channel and use that to subtly blur the edges of your render into the background), adding light wrap from the background so that strong lights in the bg bleed into your foreground cg, and adding bloom to the brighter parts of your cg so that it mimics the halation you get when film and CCD records an overexposed image.
Cheers, Simon W.