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Re: How to work on each image pixel?

From: Julien563
Subject: Re: How to work on each image pixel?
Date: Mon, 17 Oct 2016 09:51:43 -0700 (PDT)

Thx for links. My bad, i don't have clearly, exposed my problem.
I had seen the first one and the second link is very interesting with
various function to do image processing. 

I used this next function:

Octave forward me a matrix.

So, i would like to apply angular transformation in fonction of the mass of
my galaxy which has a virtual center(x,y) whith a specific radius (R). 

I call the distance between the pixel and the mass center : ralpha 

First of All : All pixels where ralpha<=R will be black (I imagine that i
must change matrix value by 0 for these point?)
Next : All points vers ralpha>=R will be affect by an angular (and
intensity) transformation (deltaO)
delta(O)= La/sqrt(x1²+y1²) where "La" is a cst.
delta(O) have 2 components : x and y components to apply the 2D

Next Problem : How to tell to Octave to mesure the distance between pixel
and the center of the Mass? Because the center of the mass will be express
in a classical (x,y) base and not in a matricial base. I don't know how to
do the link between pixel position in the matrix and center of my mass in my
(x,y) base. 

And last question : If i apply these transformations in A matrix, i will
lose in image quality? Because when i transformed my image in A matrix,
Octave noticed that :

"Warning : Your Version of GraphicsMagick limits images to 8 bits per pixel"

That's why i would like to know if it could be better to call the image in
an other way to keep the original quality picture. But if i must do that, i
don't know how... :/ 

Excuse me for my expression, but i'm not english.

Thx in Advance 

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