Blender's renderer provides partially blackened images on this .blend file #50504

New Issue

Sydney Erickson · 2017-01-23T04:38:31+01:00

Sydney Erickson commented

2017-01-23 04:38:31 +01:00

System Information
Windows 10 Home 1607 (OS Build 14393.693)
NVIDIA GeForce GTX 960M 4GB

Blender Version
Blender 2.78a e8299c8 (2016-10-24 12:20)

Short description of error
Using this blend file and rendering it with 1 sample. I used a CPU based render for this example, but a GPU based render produces the same effect. It also seems to happen regardless of image format. I tried jpg, png, tiff, and bmp.

Opening the resulting image in Blender shows that the blackness exists in the file, not just Paint

Render of the default scene using the same render settings, same install

Exact steps for others to reproduce the error

Install Blender
Open the .blend file
Set render samples to 1
Render
Export the image to a file

**System Information** Windows 10 Home 1607 (OS Build 14393.693) NVIDIA GeForce GTX 960M 4GB **Blender Version** Blender 2.78a e8299c8 (2016-10-24 12:20) **Short description of error** Using [this blend file ](https://s3.amazonaws.com/ezs3ac34a26aa3f5ce6650303da779cb7c9b/BlenderGuru+-+Cobblestone+Street+Final.blend) and rendering it with 1 sample. I used a CPU based render for this example, but a GPU based render produces the same effect. It also seems to happen regardless of image format. I tried jpg, png, tiff, and bmp. ![unknown.png](https://archive.blender.org/developer/F438610/unknown.png) Opening the resulting image in Blender shows that the blackness exists in the file, not just Paint ![unknown (1).png](https://archive.blender.org/developer/F438612/unknown__1_.png) Render of the default scene using the same render settings, same install ![untitled2.png](https://archive.blender.org/developer/F438616/untitled2.png) **Exact steps for others to reproduce the error** 1. Install Blender 2. Open the .blend file 3. Set render samples to 1 4. Render 5. Export the image to a file

Sydney Erickson commented

2017-01-23 04:38:31 +01:00

Changed status to: 'Open'

Sydney Erickson commented

2017-01-23 04:38:31 +01:00

Added subscriber: @sydney112

Joey Ferwerda commented

2017-01-24 15:44:02 +01:00

Added subscriber: @TheOnlyJoey

Sergey Sharybin was assigned by Joey Ferwerda

2017-01-24 15:44:02 +01:00

Joey Ferwerda commented

2017-01-24 15:44:02 +01:00

I tested with 520afa2962 and rendering with 1, 2, 5 and 50 samples resulted in exact the same cut-off.

Seems quite bad, assigning to Sergey

I tested with 520afa2962 and rendering with 1, 2, 5 and 50 samples resulted in exact the same cut-off. Seems quite bad, assigning to Sergey

Ray Mairlot commented

2017-01-24 17:55:22 +01:00

Added subscriber: @RayMairlot

Sergey Sharybin commented

2017-01-25 11:38:55 +01:00

Changed status from 'Open' to: 'Archived'

Sergey Sharybin closed this issue

2017-01-25 11:38:55 +01:00

Sergey Sharybin commented

2017-01-25 11:38:55 +01:00

This isn't really a bug of blender, but rather a misconfigured setup. What's happening is:

Compositor translates background sky top by 800 pixels
Then the background is mixed as a backdrop

What this causes is that there are all the pixels below 800 pixels are all colored but have alpha of 0 (because this is coming from translating backdrop up). When you're saving such file the alpha gets converted from premultiplied to straight alpha, which makes it black (because of 0 alpha).

What you can do is to set alpha to 1 for the compositor output.

There might be some improvement here, but this is how alpha was always behaving in compositor, so changing it now will likely break existing scenes. Maybe during 2.8 series we'll get to reconsiderations in this area tho.

Thanks for the report, but not really a bug.

This isn't really a bug of blender, but rather a misconfigured setup. What's happening is: - Compositor translates background sky top by 800 pixels - Then the background is mixed as a backdrop What this causes is that there are all the pixels below 800 pixels are all colored but have alpha of 0 (because this is coming from translating backdrop up). When you're saving such file the alpha gets converted from premultiplied to straight alpha, which makes it black (because of 0 alpha). What you can do is to set alpha to 1 for the compositor output. There might be some improvement here, but this is how alpha was always behaving in compositor, so changing it now will likely break existing scenes. Maybe during 2.8 series we'll get to reconsiderations in this area tho. Thanks for the report, but not really a bug.

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Blender's renderer provides partially blackened images on this .blend file #50504