Mask and PNG #45622

New Issue

José Ricarte · 2015-07-30T18:00:27+02:00

José Ricarte commented

2015-07-30 18:00:27 +02:00

When render in the compositor the node "Matte_Keying" and output to PNG RGBA, only Alfa pixels are write "1", but the previous values of RGB color of the pixels with alpha 0 remains , that means that the weight of the image is still large, the pixel information with alpha=0 should also be unified to black for PNG compression to take effect
see images:

The same image

458 k
8 M!!!!

nodes:

When render in the compositor the node "Matte_Keying" and output to PNG RGBA, only Alfa pixels are write "1", but the previous values of RGB color of the pixels with alpha 0 remains , that means that the weight of the image is still large, the pixel information with alpha=0 should also be unified to black for PNG compression to take effect see images: The same image ![0001.png](https://archive.blender.org/developer/F216153/0001.png) 458 k ![0652.png](https://archive.blender.org/developer/F216156/0652.png) 8 M!!!! nodes: ![nodes.jpg](https://archive.blender.org/developer/F216159/nodes.jpg)

José Ricarte commented

2015-07-30 18:00:27 +02:00

Changed status to: 'Open'

José Ricarte commented

2015-07-30 18:00:27 +02:00

Added subscriber: @ciriaco

José Ricarte commented

2015-07-30 18:18:19 +02:00

This comment was removed by @ciriaco

*This comment was removed by @ciriaco*

José Ricarte commented

2015-07-30 18:25:12 +02:00

If you open the two images in the composer without applying transparency "use alpha" will see that the image of 8M still has the RGB information in the transparent pixels

Blender output render image (PNG, RGBA, 5% compression ratio): 8 M !!!!

Open the image 8 M in gimp, and save again but this time with the option
"not save values on transparent pixels" and 10% compression ratio, the image now weighs 458 K

Gimp saved 458 k

If you open the two images in the composer without applying transparency "use alpha" will see that the image of 8M still has the RGB information in the transparent pixels Blender output render image (PNG, RGBA, 5% compression ratio): **8 M !!!!** ![2.jpg](https://archive.blender.org/developer/F216173/2.jpg) Open the image 8 M in gimp, and save again but this time with the option "not save values on transparent pixels" and 10% compression ratio, the image now weighs 458 K ![gimp.jpg](https://archive.blender.org/developer/F216197/gimp.jpg) Gimp saved **458 k** ![1.jpg](https://archive.blender.org/developer/F216171/1.jpg)

Sergey Sharybin commented

2015-07-31 14:04:33 +02:00

Added subscriber: @Sergey

Sergey Sharybin commented

2015-07-31 14:04:33 +02:00

Changed status from 'Open' to: 'Archived'

Sergey Sharybin closed this issue

2015-07-31 14:04:33 +02:00

Sergey Sharybin self-assigned this 2015-07-31 14:04:33 +02:00

Sergey Sharybin commented

2015-07-31 14:04:33 +02:00

That is a wrong assumption that channels with zero alpha should be black. PNG is a straight alpha as per standard and blender follows that. You can still force transparent pixels to be black in compositor tho, so wouldn't consider it a bug.
Thanks for the report anyway.

That is a wrong assumption that channels with zero alpha should be black. PNG is a straight alpha as per standard and blender follows that. You can still force transparent pixels to be black in compositor tho, so wouldn't consider it a bug. Thanks for the report anyway.

José Ricarte commented

2015-07-31 16:14:27 +02:00

Hello, I think it's a bug Because if I try to make transparent pixels RGB value to black, also recording RGB information and no compress, the image is still weighing 8 M

I think that there should be an option in the PNG output to not record RGB values in the transparent pixels as in gimp. This is important to save memory in long productions

http://thesecondmanproductions.blogspot.com.es/
https://www.youtube.com/watch?v=FAC4m11p4KI

Thanks for your work

Hello, I think it's a bug Because if I try to make transparent pixels RGB value to black, also recording RGB information and no compress, the image is still weighing 8 M ![blender.jpg](https://archive.blender.org/developer/F216399/blender.jpg) I think that there should be an option in the PNG output to not record RGB values in the transparent pixels as in gimp. This is important to save memory in long productions http://thesecondmanproductions.blogspot.com.es/ https://www.youtube.com/watch?v=FAC4m11p4KI Thanks for your work

Sergey Sharybin commented

2015-07-31 16:33:16 +02:00

There is no such thing as "not record RGB values in the transparent pixels", all the pixels do exist in the file.

Also i can't confirm here that making RGB channels black for alpha=0 doesn't help. It sames like 4x of the image size. It's hard to compare it with the result of gimp you're having because your 8meg file and 400kb files are made from different frames.

Here's an example of how you can do the trick for RGB colors: png.blend

There is no such thing as "not record RGB values in the transparent pixels", all the pixels do exist in the file. Also i can't confirm here that making RGB channels black for alpha=0 doesn't help. It sames like 4x of the image size. It's hard to compare it with the result of gimp you're having because your 8meg file and 400kb files are made from different frames. Here's an example of how you can do the trick for RGB colors: [png.blend](https://archive.blender.org/developer/F216403/png.blend)

José Ricarte commented

2015-07-31 16:53:02 +02:00

Hi,

"There is no such thing as "not record RGB values in the transparent pixels", all the pixels do exist in the file."

in gimp yes:

Hi, "There is no such thing as "not record RGB values in the transparent pixels", all the pixels do exist in the file." in gimp yes: ![gimp.jpg](https://archive.blender.org/developer/F216413/gimp.jpg)

José Ricarte commented

2015-07-31 17:10:22 +02:00

Thanks for the example !!

A bit complicated for artist... not very intuitive.

I think is better the solution of gimp... press a buton "not save the RGB values in trasparent pixels"

Thanks for your work

Thanks for the example !! A bit complicated for artist... not very intuitive. I think is better the solution of gimp... press a buton "not save the RGB values in trasparent pixels" Thanks for your work

José Ricarte commented

2015-07-31 19:26:31 +02:00

"Also i can't confirm here that making RGB channels black for alpha=0 doesn't help. "

Hi, I think that yes it helps, because the PNG compressor groups all the same RGB value pixels in an indexed list. The important thing is that transparent pixels have the same RGB value (black or color you want) then compression acts.

"Also i can't confirm here that making RGB channels black for alpha=0 doesn't help. " Hi, I think that yes it helps, because the PNG compressor groups all the same RGB value pixels in an indexed list. The important thing is that transparent pixels have the same RGB value (black or color you want) then compression acts.

José Ricarte commented

2015-08-01 16:08:43 +02:00

I researched a bit and I made a comparative test:

Base frame 8 M:

Saved : PNG RGBA, 15% compression, pixels alfa=0 with RGB initial values = 2,8 MB

Saved : PNG RGBA, 15% compression, pixels alfa=0, with RGB= black= 1,6 MB

With transparent pixels normalized to black: aprox -40% storage use

I researched a bit and I made a comparative test: Base frame 8 M: ![0258.png](https://archive.blender.org/developer/F216842/0258.png) Saved : PNG RGBA, 15% compression, pixels alfa=0 with RGB initial values = 2,8 MB ![B1.png](https://archive.blender.org/developer/F216830/B1.png) Saved : PNG RGBA, 15% compression, pixels alfa=0, with RGB= black= 1,6 MB ![B2.png](https://archive.blender.org/developer/F216839/B2.png) With transparent pixels normalized to black: aprox -40% storage use

Sergey Sharybin commented

2015-08-03 11:04:52 +02:00

PNG's compression exploits color similarity across the Y axis of the image, so surely increasing this similarity (by setting colors to black) improves compression and reduces overall file size.

It would be nice to have a tool to make operation of setting transparent pixels to black, but it's out of the scope of the bug tracker.

PNG's compression exploits color similarity across the Y axis of the image, so surely increasing this similarity (by setting colors to black) improves compression and reduces overall file size. It would be nice to have a tool to make operation of setting transparent pixels to black, but it's out of the scope of the bug tracker.

José Ricarte commented

2015-08-03 12:53:41 +02:00

Thanks for your reply, yes, it would be interesting to develop this tool Because it would help the films production in blender. = :-)

Sorry for the noise in the channel

Thanks for your work

Thanks for your reply, yes, it would be interesting to develop this tool Because it would help the films production in blender. = :-) Sorry for the noise in the channel Thanks for your work

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Mask and PNG #45622