Rescale Tool

[llpastro]

What is happening when the Rescale tool is used?  I have looked around for an explanation but so far have not found one.

Larry

[oldwexi]

Hi Larry!
to my knowledge and very simplified - if you have an image where the beginning of the histogram does not start at the left side at 0.0
but at 0.2  - the rescale does move the beginning of the histogram to the left side.
So, it scales all pixels with values from 0.2 to 0.9999  to the corresponding values between 0.0 to 0.9999
This can increase the contrast.
To be frank, i never ever used this tool in all my image processing years...
i think it is a relict of ancient PI times.

Gerald

[llpastro]

Gerald, thanks for the reply and that is what I thought.  I wasn't sure since when I Google Rescale on the internet, all of the references were to Resizing and I didn't think that was right.  The question came up in my mind when Harry of Harry's Astro Shed used it briefly in one of his videos but was using it to demonstrate something else.

If anyone out there is using it, I would be interested to know when it is appropriate.  Seems like the histogram tool is sufficient.

Larry

[Carlos Milovic]

Yes, is used to quickly rescale everything on the [0,1] range (1.0 included, not 0.9999). For color images, there is an option to rescale to the absolute minimum and maximum, or each channel's minimum and maximum. This may be useful after noise reduction, to gain quickly a bit more contrast, from the now unused parts in the shadows (of the dynamic range).

Another field of application (where I use it a lot) is to rescale images that have out of range values (lower than 0.0 or larger than 1.0) as happens with some professional astronomical data stored in 32bits floating point fits files, and files comming from medical DICOM format...

[llpastro]

Carlos, thanks for the feedback. 

Larry