The healing brush tool

I have posted some notes and images demonstrating these effects on my web site at http://www.corybas.com/Technical/Hbt.htm

James McNangle

I was recently amusing myself trying to repair an old photo, and when I tried to
use the healing brush tool (HBT) I realised I didn’t really understand what it
did. I did some research to discover just what it did do, and as some recent
discussion indicated that others were equally confused, I decided to report it
here.

The HBT is similar to the clone stamp tool (CST), but with a subtle difference.
Whereas the CST simply replaces the contents of the target area with the contents of the reference area, the HBT blends the detail in the target area as
you move away from the boundaries and copies details from the reference area.
If there is no detail in the reference area nothing is copied, so that the tool
simply blurs the target area. This applies even if the reference area is a
different colour. If there is detail in the reference area this detail is copied into the target area, and blurred into the original contents around the
margins so that you do not get a sharp discontinuity.

This freedom from sharp discontinuities is probably the main virtue of the HBT,
but it comes at a cost, in that the blurring action can seriously distort any
sharp discontinuities in the target area. If, for example, you are working in a
light coloured area adjacent to a dark border, and you accidentally include a
bit of the border in the target area, it will bleed into the target area as a
very obvious dark smudge. The Photoshop users manual states that this can be
avoided by selecting the area you want to work on before you start to copy.

The HBT is probably at its best in areas with subdued detail, whereas the cloning tool is better for areas with sharp discontinuities. If, for example,
you had an image with a frame, and silverfish had eaten holes in the frame, the
cloning tool would probably do a better repair job. Unfortunately it is not
easy to position either tool accurately, and you cannot adjust the position of
the copy once you have placed it. If precise alignment is needed it may be
better to use the marquee tool to select a good area, and then copy this and
paste it where you need it. This has the advantage that after you have pasted
it you can move it into just the right position. In an extreme case you could
even rotate, distort or trim the new section to align it correctly after you had
placed it.

I have posted some notes and images demonstrating these effects on my web site
at http://www.corybas.com/Technical/Hbt.htm

James McNangle