PHOTOSHOP - oddities in scaling routines with layermasks

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  • Updated 3 years ago
  • (Edited)
Scaling a layer that is partially transparent results in totally different image compared to using a layer with a layermask.
The reason might be that a layer has undefined values outside its dimensions, whereas the layer with layermask always has the full image dimension.

To verify:
make a 10x10px image.
Color the background blue (0,0,255)
Create a layer with a centered 6x6px red (255,0,0) rectangle with sharp edges on top.
Duplicate this layer and convert it to layer with mask from transparency
Duplicate the layer with the initial red box and place two additional green pixel in top left and bottom right corner.

scale the whole thing to 100x100 pixels with bicubic automatic.

The layer with only the red box will not have any change on the blue side and incredibly sharp edges.
The same layer with the two additional green pixels will look totally different as now the layer extends over the full dimensions and everything is now scaled, not just what is inside the new layer.

Another interesting fact: again perform the layer->layer-mask from transparency on the now scaled red box with green pixels. Look at the rgb data. It is not symmetric at all, even though the source was symmetric. Shouldn't that be symmertical?

I could supply a psd that just needs to be scaled, but I'm limitted to png or jpg...
here without the green pixels

And here with them:

PS CS 6.0, 13.0.1 x64
Photo of oliver bartosik

oliver bartosik

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Posted 3 years ago

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