Selecting centre Displace in Circular mode

[tomczak]

This question is related to the tip here:

http://www.dl-c.com/board/viewtopic.php?f=5&t=576

I can't figure out how to move the centre of 'shrinking' from the actual centre point of the image. This would be useful if the portrait in the example above was off-centre. Would it be practical to be able to choose the centre in Displace transformation (in a similar manner as it is possible in Distortion transformation - or perhaps being able to use mask in Distortion which could serve similar purpose)? Cheers!

[ksinkel]

You can contol the amount of displacement with a mask. I would suggest trying to create a circular gradient centered on whatever point you like and using that as a mask to control displace. There is an example of displace through a gradient mask in the manual. See "Using Circular Displace..." in the Displace section of Chapter 14, Using Special Effects.

Kiril

[tomczak]

While the off-centre mask will only displace the off-centre pixels, they can only be displaced towards the physical centre of the image, not the centre of the mask, I believe.

I can't illustrate it at the moment, but with the example in the tip above, if the face I wanted to 'shrink' was off-centre, then covered by mask as usual, the face pixels will be displaced towards the centre of the image, which will distort the face asymetrically, in an unintended way.

Is there an way around it? The only way I can think of is to crop the image so that the face is in the centre of the crop, apply the 'diet technique', then use the Composite to put the processed crop back in place. But the positioning the processed crop back where it belongs may be quite finicky - I don't know how to place it back exactly where it was other then trying to do that by hand, while being guided by the results in the preview.

[gio]

Maybe you can expand the image so that the face is in the center, then distort it, and crop to the original dimension?
Its just a workaround though.

[ksinkel]

I didn't mean to imply that the mask changes the center of the circular displacement. That remains unchanged. What it does is change the degree to which the transformation is applied. So whether or not a mask will help depends on the effect you want to achieve. However as you point out, adding a border to change the center to your desired location, applying the transformation and then cropping will work.

Kiril

[tomczak]

Adding a border to center the image, applying the transformation, then cropping it back again (instead of what I figured: i.e. cropping it first to center, then trying to composite it back onto the original image) is much better idea! Thanks!