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Render out PNG sequence with bounding box

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Chad Ridgeway
Render out PNG sequence with bounding box
on Sep 6, 2012 at 6:00:59 pm

I want to render out a PNG sequence with bounding box (based on alpha channel) to cut down on file size. (it's a 720p sequence with a pretty small character moving around)

How can I do this in After Effects without having to run it through Nuke's bounding box tool?


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Dave LaRonde
Re: Render out PNG sequence with bounding box
on Sep 6, 2012 at 6:34:39 pm

If the bounding box is rectangular, you can nest the main comp in one with a smaller horizontal & vertical resolution, position to taste, and render: no alpha channel needed.

-- OR --

If you can't position the video in the next application, nest the main comp in one of identical size, make a solid in the appropriate dimensions for the bounding box, use the solid as a track matte and render.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Chad Ridgeway
Re: Render out PNG sequence with bounding box
on Sep 6, 2012 at 6:37:52 pm

Ok but my character is moving all over the screen, so I need an animated bounding box, and I'm thinking basing it off the alpha channel would be the easiest thing for AE to calculate.


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Dave LaRonde
Re: Render out PNG sequence with bounding box
on Sep 6, 2012 at 7:16:43 pm

Okay, it's now time to ask what you're trying to accomplish by using this bounding box: is the original composition too big to be used for the files you need to deliver using AE, for example?

Tell us about the original comp's specs and the specs you need to deliver. Then we stand a fighting chance of offering advice you can actually use.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Walter Soyka
Re: Render out PNG sequence with bounding box
on Sep 6, 2012 at 7:10:47 pm

[Chad Ridgeway] "I want to render out a PNG sequence with bounding box (based on alpha channel) to cut down on file size. (it's a 720p sequence with a pretty small character moving around)..."

[Chad Ridgeway] "Ok but my character is moving all over the screen, so I need an animated bounding box, and I'm thinking basing it off the alpha channel would be the easiest thing for AE to calculate."

The transparent areas of the raster should compress very efficiently. I don't think you'd actually save much space at all.

If you did a bounding box crop on each frame, how would use this animation elsewhere? All the positioning within the raster will be gone, and you won't have a consistent anchor point.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Chad Ridgeway
Re: Render out PNG sequence with bounding box
on Sep 6, 2012 at 7:24:15 pm

Ok guys, the bounding box actually does cut down on the file size pretty dramatically, and is extremely useful and common place in visual effects when you're dealing with multiple elements and want to cut down on file size and processing power.

If you still don't get what I'm talking about, the first few minutes of the Nuke bounding box tutorial (



) should make it's purpose completely clear.

I just ran my animation through Nuke (autocropped with the bounding box) and re-imported it and AE did not like it, so maybe AE just isn't made for it.


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Walter Soyka
Re: Render out PNG sequence with bounding box
on Sep 6, 2012 at 7:53:08 pm

[Chad Ridgeway] "Ok guys, the bounding box actually does cut down on the file size pretty dramatically, and is extremely useful and common place in visual effects when you're dealing with multiple elements and want to cut down on file size and processing power."

I know what you mean -- but when in Nuke, think like Nuke. When in AE, think like AE. A good Nuke workflow is not necessarily a good AE workflow, and vice versa.

Bounding boxes are a perfect example. AE has no bbox tools; there's no way for the user to dynamically change the area considered for processing for a layer in AE.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Chad Ridgeway
Re: Render out PNG sequence with bounding box
on Sep 6, 2012 at 7:55:46 pm

Yeah got it, so AE can't do it.

I will say it's not just a matter of workflow, my files after being re-rendered through Nuke with the bounding box are about half the file size.


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Walter Soyka
Re: Render out PNG sequence with bounding box
on Sep 6, 2012 at 8:17:17 pm

[Chad Ridgeway] "I will say it's not just a matter of workflow, my files after being re-rendered through Nuke with the bounding box are about half the file size."

Personally, I care about the RAM and CPU implications a lot more than the disk space.

If you really need to crunch the files, you can enable LZW compression in the output module's PNG format options. Note that this will trade disk space for decode complexity.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Chad Ridgeway
Re: Render out PNG sequence with bounding box
on Sep 6, 2012 at 8:48:24 pm

Yes absolutely for this project file size is at a premium. LZW compression isn't an available option for PNGs (it is for TIFs). What is your recommendation for the absolute smallest file size? (I've ran multiple tests but so far nothing is beating a PNG with a bounding box)


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Walter Soyka
Re: Render out PNG sequence with bounding box
on Sep 6, 2012 at 8:55:52 pm

[Chad Ridgeway] "Yes absolutely for this project file size is at a premium. LZW compression isn't an available option for PNGs (it is for TIFs). What is your recommendation for the absolute smallest file size? (I've ran multiple tests but so far nothing is beating a PNG with a bounding box)"

My bad -- I was thinking TIFF. PNG is already compressed (with deflate).

PNG may be tough to beat. If you can deliver 8b, and if your image has large areas of flat color, TGA with RLE compression enabled may be smaller.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Kevin Camp
Re: Render out PNG sequence with bounding box
on Sep 10, 2012 at 7:54:53 pm

depending on the animation, rendering lossless with compression keyframes enabled may create smaller files than png... in the format settings, enable the 'keyframe every xx frames'.

the effectiveness of compression keyframes can vary greatly based on the animation, but you could give it a try.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW


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