[Numpy-discussion] np.histogram on arrays.

Éric Depagne eric@depagne....
Wed Mar 30 05:44:13 CDT 2011


> 
> Well I guess, for a slight performance improvement, you could create your
> own streamlined histogrammer.
> 
> But, in order to better grasp your situation it would be beneficial to know
> how the counts and bounds are used later on. Just wondering if this kind
> massive histogramming could be somehow avoided totally.
Indeed.
Here's what I do.
My images come from CCD, and as such, the zero level in the image is not the 
true zero level, but is the true zero + the background noise of each pixels.
By doing the histogram, I plan on detecting what is the most common value per 
row. 
Once I have the most common value, I can derive the interval where most of the 
values are (the index of the largest occurence is easily obtained by sorting 
the counts, and I take a slice [index_max_count,index_max_count+1] in the 
second array given by the histogram).
Then, I  take the mean value of this interval and I assume it is the value of 
the bias for my row. 

I do this procedure both on the row and columns as a sanity check.
And I know this procedure will not work if on any row/column there is a lot of 
signal and very little bias. I'll fix that afterwards ;-)

Éric.


> 
> Regards,
> eat
> 

Un clavier azerty en vaut deux
----------------------------------------------------------
Éric Depagne                            eric@depagne.org


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