selecting a part of the picture to process

[cherodotou]

Hello,

This is a picture of a brick from a scanner. I want to process just the brick in PixInsight, how can I do this? Bear in mind that the edges of the brick have an irregular and curvy shape.

Thank you.

[georg.viehoever]

Create a mask that selects the brick, and apply it to the brick image. After that, all operations are limited to the brick pixels.
Georg

[Carlos Milovic]

To create the mask, just extract the luminance, and apply a threshold (Binarize process).

I think that for most operations, you'll be fine with the mask. There may appear some boundary artefacts if you use convolutions or morphological filters, but in general it won't be a problem.
Oh, btw, if you want to extract statistical parameters, the easiest way is to create a preview inside the brick.