Noise introduced when rotating a group

[jl_678]

Hi,

I have found a very odd behavior from Photoline and my guess is that it is a bug. It appears to happen consistently and so I am trying to understand exactly what is going on. Here is what I do:

1. Open an image with a base layer
2. Add a layer and do a minor modification (I use copy brush)
3. Create a new group containing both layers from 1 and 2
4. Use "Rotate Layer" function and rotate the group -> the minute you rotate the group, noise increases significantly on the combined image

Compare with:
Follow steps 1 & 2 above
3. Rotate the base layer using "rotate layer" function
4. Rotate the second layer using "rotate layer" function
5. The result is the same as step 4 above EXCEPT there is no new noise.

I am trying to understand if this is a bug or if something else is going on. Any guidance would be appreciated.

Details: The latest version of PL on Win7.

Thank you,

JL

[Hoogo]

I guess you will see the same effect when you just rotate a layer using the layer tool (the black arrow).

When you activate the tool, the layer handles are shown, and when you point a little outside of the corners, the mouse icon changes into a symbol for rotating. Does the noise appear, too, when you rotate the layer a little using this tool?

Now try the antialias-button that you can find in the upper toolbar. Does the noise decreae when you press that button?

And last experiment: When you rotate the layers using "rotate layer" function, what method did you choose? When you try "quick", do you receive the same noise that appears with the first method?

[jl_678]

Hi,

I used the rotate tool in the top toolbar called the "General" tool bar. The icon is the same as that found under "Layer/Rotate Layer." I also see the same problem if I go to "Layout/Page/Rotate Page". The behavior is also the same if I use the generic "Rotate 90 degrees" option in the "General" toolbar. Note, that from testing the same problem I mentioned hold consistent that if I rotate a layer, it works fine, but that rotating a group causes the noise/pixelation.

Regarding you question about rotating cursor symbol, I have used that too with the same results. (e.g. rotate the group and the pixelation appears.)

Finally, I did check the anti-alias button and can see no meaningful difference.

To the extent it matters, I am working on a 16-bit TIFF file that I imported from Lightroom 4.1. This is a converted RAW file and the output is 240 DPI.

Is anyone else seeing this?

JL

[Hoogo]

Can you see the same when you view the picture at a zoomlevel of 100%? Does it disappear when you reduce the group to one layer after the rotation?
Otherwise, when the problem occurs for rotations of 90°, then I have no more ideas... Can you make screenshots at a zoomlevel of 100% and upload a before/after?

[bkh]

I can see differences at zoom levels below 100 % (especially where there's a lot of fine details in the image). At 100 %, I can't see any difference. This even happens if you don't do any edits but just create a group containing the image itself. Turning global antialiasing on in the "General" toolbar improves the situation but doesn't entirely solve the problem.

The reason behind this behaviour is that PL has two different kinds of rotation: destructive rotation which changes the pixels in the image layer (used for bitmap images), and non-destructive rotation, where PL just remembers the rotation angle and the image layer remains unchanged (used for vector layers and groups, but also for ordinary layers if you rotate them using the layer tool). In the non-destructive case, the rotated image is computed on the fly when the image is displayed, which (for efficiency reasons, I suppose) can result in lower display quality at some zoom levels.

In any case, as far as I can see, this is just a display effect but doesn't affect the final image.

Cheers

Burkhard.