Network rendering Best Practices

[rwhunt99]

I ran into some problems rendering a scene and tried to do some research and the manual has a very pathetic and anemic section about rendering and also rendering on the network. I am looking for some reference, and guides to getting the best renders not only normally, but on the network rendering also. Since this is a visual medium, I would have hoped they would provide a very good section on this.

One of my problems was banding, things looked great in the view port, but by the time I rendered it out, there was significant banding in the background. I tried several different variations and file formats but always got banding. Is this normal? It is an underwater scene. the background was a gradient, I also tried an image world but I did use a gradient in that also. I would like a tutorial in how to get good renders, I have had problems ever since I think LW10, or when they went to linear colorspace, I tried that and sRGB also but got the same results. This image is a raw image direct from LW11.6, I then re-ran the image sequence through LW to create an AVI and it looked absolutely horrible. I am not sure the codecs are up to date, or what is going on. I ran the sequence through AE and applied film grain but it kind of defeats the purpose of having any small details when you have to dirty it up to hide the banding. I know I don't know what I'm doing, but it's frustrating to not be able to find any resources on how to get the results you want.

 

[ernpchan]

Do your F9s look bad? Rendering on the network should recreate what your local F9 renders.

I compile frames into a video file through AE into quick times. I use either the Animation or the DnxHD codec.

 

[Danner]

I've run into banding before. Below are some things I've learned.

Jpegs are a lossy compression format and they can introduce banding on subtle gradients, some tones are very sensitive. (0r maybe our eyes are very sensitive to some tones). Video compressors are worse even.
Even on unconpressed formats you can get banding and that is where dithering can help (effects window, prcessing tab)
In some extreme cases I've had to render out as RLA or EXR at a higher bit depth to get rid of the banding.

 

[rwhunt99]

Thanks for the help.
the image I posted is an image from a render I did. I don't know how well you can see it, but there is a lot of banding. I used the gradient background, I don't recall having problems before. The fist time, I rendered and I used a 24 bit PNG, and I didn't realize that AE doesn't handle those, so I rendered again with JPEG, as I figured it was universal and I didn't really need an alpha channel anyway. I think I understand what you are saying about compression though, and then you are running it through a video codec and getting compressed again. What is a recommended format (file type) to use? I am using motion blur (photo real), I am not sure what dithering does, I saw it in the motion blur type drop down, but I don't think that is what you meant. When I did bring it into AE, I wasn't sure how to get rid of the banding (hide it) so I used several different effects, like film grain, but I couldn't get rid of the banding

 

[ernpchan]

AE handles PNG files...I use them all the time.

Can you share the scene that's making that image?

 

[rwhunt99]

You are right, they do handle PNG's @ 16 bit, I tried it using 24 bit and it doesn't work, I got on Adobe's help site and checked it out. I'm going to render the scene again and I'm going to throw a layer or two of turbulence onto an image world gradient and see if that helps, and I'll try PNG's again this time at 16bit, I don't really need an alpha channel for this. If I still have trouble I will try to put the scene (it is a tutorial on flocking) here for you to look at.

 

[Danner]

I use PNGs all the time in AFterfx, what seemed to be the problem with them? If the backdrop doesn't show in afterFX you need to edit the footage import settings and turn alpha off.

Dithering tries to avoid banding by adding noise to the image to simulate half tones, as I said before it's not needed all the time, but some gradients don't have enough information to avoid banding. Try the settings on the attached image to test dithering for yourself.



I am using sRGB, if you are using a different color-space things might look different But the concept is the same, low contrast gradients will get banding in any software, yes even in Photoshop.

 

[rwhunt99]

I use AE Cs5.5; I couldn't get it to load my images that were saved with LW_PNG24, I re- rendered then using TGA and I still have banding. I will try using that dithering and see how it looks.

 

[Danner]

One thing I forgot to mention is that you can work in 16bits per channel in afterfx, and that also helps when the banding comes from color corected gradients. At the bottom of the project tab you should see "8 bpc" alt click once.

As a side note there is a confusing aspect about this bits thing is that some files talk about total bits, other file types refer to bits per channel. So what is commonly known as a 16bit Tiff file is 16 bit per channel so it has more data and is a much larger file than what is commonly refered to as a 32bit PNG. (8 bits per channel inclunding alpha RGBA 8+8+8+8=32 )

 

[ernpchan]

In AE you could try adding a small amount of noise and then some blur on top of that. If your gradient doesn't have enough of a color spread you'll get some banding as you don't have enough colors to cover your space. If you have the Genarts Sapphire suite it comes with a Debanding effect.