How to create an equation of a line with Matrix?

Hello,

I attached an image here and it is a matrix of 22x100.

fxy_2 = new_twenty_proj(329:350,222:321);

This is my fxy_2.

You can see at the upper left that there are a few numbers there. I was told that I need to use something like mx+b or equation of a line to get rid of those numbers. like if mx+b > (something over here), then I would only care about the numbers at the other part, not the ones on the upper left.

I don't know how to do this, though. I'm just a beginner in matlab and I read that i can use refline or polyfit or even regress.

Can anyone help me?

Thank you!

[Jan]

What do you want to do? Do you want to set the two values in the upper left corner to 0?

[Kash Costello]

Yes! Or if I get the equation of the line, I need to say that the upper part of that line will not be part of my data set and the only ones I need are the ones below the line. (Does that make sense?)

I also have other set of data (something like this, and they are overlapping so I also need to do the same thing.

[Jan]

I do not understand which line you are talking about. What is the "upper part" of a line - or in other words: where is "above" exactly? What is overlapping?