Scale Filter rotated sources - not working?

strobey

New Member
Hi,

If I scale filter a rotated source the filter does not appear have any effect. Have tried the following permutations:
0deg - OK
90deg - BAD
180deg - OK

I have tried both an image and also a BMD video source and see the same issue.

I have searched for anyone with a similar issue but couldn't find anyone. Can anyone confirm if they see the same behaviour as me?

Thanks
OBS 25.0.8 / 64bit on Windows 10
 

koala

Active Member
Works for me. 90° CW, and also with arbitrary rotation values. In the properties of the filter, I changed through all "scale filtering" methods in the dropdown list and saw an immediate change in the preview.
What do you intend to use the scale filter for? It's for changing aspect ratio, that is to either rectify distorted images that come with wrong aspect ratio, or to distort correct images for some player that expects distorted images and straighten this internally.

If your filter does not actually change aspect ratio, because perhaps the source has already the destination aspect ratio, no change will be visible. I tested with an 16:9 image that I distorted to 1:1 aspect ratio. For changing between bilinear, bicubic and lancos I wasn't really see any difference in the preview, but the other methods were visible very well.
 

strobey

New Member
Hi,
Thanks for reply and for taking the time to check.

We might be looking at two different places, albeit similar actions.. I'm right-clicking on a source and going directly to the "Scale Filtering" menu, not the Filters dialog. From here I choose Lanczos.

I'm using this to improve the image on a highly scaled-down input source (imagine a small Picture-in-Picture), not changing the aspect at all.

Can you replicate?

Thanks again..
 

koala

Active Member
Works for me as well. 0°, 90°, 33° - all visible changes. This filtering is used when OBS scales up or down a source to a different size. Usually, differences are very subtle. Depending on the source material, you might not see anything for bilinear, bicubic or lanczos, especially if it is some smooth material with no sharp edges. To really see changes with these, you may need to compute the difference between two images with different filters with some painting app. If the difference picture is completely black, it's the same filtering, and if you see shades of black and gray, you see the differences between the filters.

The most prominent changes (but not necessarily the best filter) you will see without the use of a painting app is with point or area filtering. These filters are intended for special sources such as high contrast pixelated material such as 8-bit console images or black/white images or images with just a few colors without shades. You don't use these for normal material, but they are good to demonstrate that scale filtering works in general.

Don't expect magic. No filter can add detail that isn't in the original source.
 

strobey

New Member
Thanks koala,

Yes I appreciate the nuances of scaling, not magic as you say, however my video source does indeed have some very sharp edges and so it looks awful when scaled down without some element of image filtering.

If you're not seeing this then there must be something particular to my version/config. Hmm.

As a test I have just imported a brand new image into a new profile and was able to repeat the problem.
Both sources here are scaled down approx 50% and Area scale filtering applied to both which works well for b&w text.

The only different is one is rotated 90 degrees. The rotated image you can see does not get filtered on scale.

Anyone else seeing this?


scale-fail-rotate.png
 

Attachments

  • obs-log-strobey-20200719.txt
    4 KB · Views: 21
  • scale-fail-rotate.png
    scale-fail-rotate.png
    145.5 KB · Views: 17

strobey

New Member
OK, more on this... for me the Lanczos or Area scale filtering get progressively worse as you approach 90 degrees of rotation and then progressively better between 90 and 180 degrees, at which point it's perfect again.

I think this has something to do with which operation comes first, the scale operation or the transform (rotate).

But I need to find someone who can repeat these steps and get the same output before I think on that any further.

Thanks!
 
Top