GNOME Bugzilla – Bug 167638
Curve Bend Smoothing/AntiAlias doesn't work on the alpha channel
Last modified: 2018-05-24 11:25:47 UTC
In a 420x300 new image window, create a text layer over a white background using the Sans Bold font @ 80 pixels. Shear the text vertically. Using the Perspective tool, reduce the right side height of the text layer. The two transforms help to visually enhance the problem. Make sure Keep Transparency for the text layer is disabled. Duplicate the image. Now use the Curve Bend filter to curve the text layer in the original image with Smoothing and AntiAliasing turned OFF. Use the Curve Bend filter with the same settings except with smoothing and antialiased turn ON in the duplicate image. By visual inspection the images appear identical. I see the same stair stepping in both, when the duplicate should not have this. If I can, I'll try to attach some sample TIFFs showing the problem.
Created attachment 37567 [details] Example TIFF with smoothing and antialiasing turned off (uncompressed) This is an example of the text when Curve Bend is run with Smoothing and Antialiasing turned off.
Created attachment 37568 [details] Example TIFF with smoothing and antialiasing turned on (uncompressed) This is an example of Curve Bend run on the same image but with Smoothing and Antialiasing turned on.
Michael, you are under the wrong impression that text layers would be any different to normal layers. Unless you use the text tool on the text layer, it is just a normal layer like any other layer. So there must be another difference.
Perhaps the smoothing/antialiasing in Curve Bend doesn't function against an alpha channel then? The text layer is mostly transparent except for the text. That might be the problem. I tried this with a transparent layer in which I made a rectangular selection and filled it with a black box. I then applied the transforms and Curve Bend and noticed the same stair step results. I also tried it without the transforms and noticed similar results. It's also possible this isn't really a bug and I'm just not seeing the results the way I should. I just assumed the stairstepping would go away with antialiasing on (at a minimum) since there was little visual stairstepping before Curve Bend was applied.
It is very easily verified that antialiasing doesn't work on the alpha channel here.
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