You're losing me. What do you mean "the intensity value along the horizontal"? It doesn't matter; you've got some data plotted in an x-y plane. The slope ("intensity rise", as you seem to call it) of the unaccepted valley looks the same as at your other valleys. There must be some other criteria you are using.the plot represents the intensity value along the horizontal. So my target is to extract the region where the intensity rises drastically hence I am not concerned about the second valley. thats the reason its becoming difficult for me.
I would improve this method with barry's advice:Then maybe something simpler like a sliding window with a check for a (MAX/MIN> threshold) AND (MINx < MAXx), that would be pretty easy to implement.
Whatever they meaned, how about trying the significance of different criteria for your data yourself?by sliding window should I calculating the moving average ? Or do you mean to calculate the min and max in the sliding window range.