Forums Technical Discussion Missing Unpremultiplied Option in New COPS File Node

Missing Unpremultiplied Option in New COPS File Node

   Views 625   Replies 9   Subscribers 2
User Avatar
maartennielen
Member
13 posts
Joined: Aug. 2017
Offline
 
In the new COPS, the file node does not have an option to load images unpremultiplied, which results in a very dark image. Since I often need to load TGA files with alpha for my work, I'm looking for a good workaround. The old COPS file node does have this option.
Image Not Found
Edited by maartennielen - March 24, 2025 04:36:21

Attachments:
example.tga (1.0 MB)

 Report
User Avatar
Heileif
Member
216 posts
Joined: Jan. 2015
Offline
 
Workarounds.

Unpremult = rgb divided with the alpha.

Premult = rgb multiplied by the alpha.
Edited by Heileif - March 13, 2025 11:18:41
 Report
User Avatar
maartennielen
Member
13 posts
Joined: Aug. 2017
Offline
 
Yeah, thanks for the fast reply. The File node gives a different outcome compared to manually premultiplying or unpremultiplying the correct image without the alpha. So I think something is broken in the File node since the results don’t match. I’ll make an example file
 Report
User Avatar
maartennielen
Member
13 posts
Joined: Aug. 2017
Offline
 
Here is an example file. I don't see any way to restore the image by dividing or multiplying with the alpha. As far as I know, this only happens with TGA files.
Image Not Found

Attachments:
example.tga (1.0 MB)

 Report
User Avatar
ajz3d
Member
617 posts
Joined: Aug. 2014
Offline
 
My guess is that you should be importing the image as Raw for the Un-premultiply (Premultiply COP) to work correctly.
In the File COP, change the "Incoming Colorspace" to "Raw", or check the "Raw" flag for the C AOV.
 Report
User Avatar
maartennielen
Member
13 posts
Joined: Aug. 2017
Offline
 
Thank you for your reply! Yeah, I also assumed that would be the solution. I think I’ve tried almost every possibility, but I have a feeling it’s a bug. I attached the TGA file in my last post if you want to try it.
Edited by maartennielen - March 24, 2025 17:41:08

Attachments:
example2.jpg (160.3 KB)

 Report
User Avatar
ajz3d
Member
617 posts
Joined: Aug. 2014
Offline
 
Now with File COP set to "Raw", drop a Premultiply COP and unpremultiply the image.
Edited by ajz3d - March 24, 2025 18:02:42
 Report
User Avatar
maartennielen
Member
13 posts
Joined: Aug. 2017
Offline
 
Thank you! It’s working now! I don’t know why I couldn’t get it to work before. I did try dividing by the alpha but got a broken result. I just tried it again, and everything seems fine now.
Edited by maartennielen - March 24, 2025 18:13:42
 Report
User Avatar
johnmather
Staff
564 posts
Joined: Aug. 2019
Offline
 
This has been fixed in 20.5.549. You can disable the new "Pre-multiply if Necessary" parm on the file node.
 Report
User Avatar
maartennielen
Member
13 posts
Joined: Aug. 2017
Offline
 
Thank you very much!
 Report
  • Quick Links
▼
  • Jump to
  • Houdini
  • News
  • Houdini Indie and Apprentice
  • Houdini Lounge
  • Technical Discussion
  • Work in Progress
  • Houdini Learning Materials
  • BYOC + Illume
  • Houdini for Realtime
  • Solaris and Karma
  • Rigging
  • Animation
  • PDG/TOPs
  • The Orbolt Smart 3D Asset Store
  • Houdini Jobs
  • 日本語フォーラム
  • Licensing
  • Houdini Engine
  • Houdini Engine API
  • Houdini Engine for Unreal
  • Houdini Engine for Unity
  • Houdini Engine for Maya
  • Houdini Engine for 3ds Max
  • Private
  • Contests
  • Mardini 2025
  • Mardini 2023
  • H20 Tech Art Challenge
  • Mardini 2024
  • SideFX Labs Tech Art Challenge 2022
  • MARDINI Daily Art Challenge 2022
  • SideFX Labs Tech Art Challenge 2021
  • MARDINI Daily Challenge 2021
  • Nodevember 2020
  • HOULY Daily Challenge
  • 3rd Party Software and Tools
  • 3rd Party
  • SI Users