Stretch and Masks bug?

[johnp]

I was playing around with an image that had some side image branches that I later deleted.

I then added a Stretch transform, then added a Brightness curve after the Stretch and noticed that The brightness transform could no longer access a mask I had made near the top of my image processing using the Mask command. In looking at the Stretch transform, I notice it does not have a button to select a mask. Is it possible the Stretch transform blocks any masks from propagating downstream?

I've attached the workspace with an extra .txt extension to make the attachment button happy.

Thoughts?

John P

[jsachs]

To be eligible for use as a mask, the mask image must have the same dimensions as the image to which you want to apply the mask. Since the stretch transformation changes the size of the image, the previous mask can therefore no longer be used. The same problem occurs if you crop, warp or rotate an image or do anything else that changes its size in pixels.

There is a way to get around this, although it is somewhat awkward:

1) Go back to the transformation you created the mask for originally
2) Save the image as an image file (via the Mask Settings menu)
3) Open the saved mask image
4) Apply a copy of the stretch transformation you used to stretch the image -- this stretches the mask the same way as the image you want to mask.
5) Finally, you should be able to use the stretched mask with the stretched image.

In hindsight, you could have avoided the problem in either to two ways:

1) Stretch the image before you started creating masks
2) Stretch the image after you are done creating masks.

I normally use method 2 and try to defer cropping or otherwise resizing images until I am done with color or brightness adjustments or other transformations that are likely to need masks. In some cases I might, for example, do a rough crop right at the beginning if I'm sure I want to remove parts of the image, and do a final stretch or crop at the end.

[johnp]

Thanks for the explanation - that makes complete sense.

John P