Scope

[Searcher1851]

The Scope set of  panels is puzzling me and in particular the "Power Spectral Density" graph.  How is it useful in Post Processing?  I have attached a screen shot of an image together with its PSD graph with a gain of 300%.  Will looking at this graph tell me how to improve the image?

 

I have watched a video on this subject, but the orator appeared to be wondering why the graph is in Affinity Photo.

 

I have noticed that if the image is predominately (say) red, then the graph is predominately red, I cannot believe that Scope is in Affinity just to make it look a little more scientific, so please, what is the purpose?

[James Ritson]

Power spectral density represents the document view in the frequency domain, so it will give you an idea of the frequencies your image is made up of. It's useful for examining the complexity of your document - more "noise" and scattering on the graph represents more high frequency detail; so sharp pixels, noise, etc. It's also useful for identifying FPN (fixed pattern noise) and periodic noise, which you can remove with the FFT Denoise filter.

 

Outside of some edge cases like astrophotography star stacking, image cleanup, etc it has somewhat limited use, but it's handy for analytical purposes. You could theoretically use it to gauge pre-processing for images to increase compressibility; for example, examining the results of denoising and other convolutions.

 

Hope that helps!

[R C-R]

If you have not already done so, it may help to read the built-in "Scope" help topic. There is a beta version of that help page available online. The US English version is at https://s3-eu-west-1.amazonaws.com/affinity-docs/help/photo/en-US.lproj/pages/Panels/scopePanel.html