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Using Photoshop for densitometry?

arturo.galvani at itner.pharmacia.se arturo.galvani at itner.pharmacia.se
Fri Dec 15 02:44:47 EST 1995

     I don't use Adobe Photoshop, but if you have a linear response between 
     amount of RNA loaded and 'densitometry' data, I don't see how anyone 
     can argue with you.  One thing you could do which might avoid reviewer 
     gripes is to calibrate your system with a photographic step tablet, 
     e.g. StepTablet No. 3 from Kodak (- no affiliation).  These are strips 
     of film exposed in such a manner to give a range of predetermined 
     O.D.s, which you could scan to find out exactly how good or bad your 
     densitometry system is.  
     Arturo Galvani
     (all views expressed 
     are strictly my own)
     Martin Hoyt (rdlab at gandalf.bio.uci.edu) wrote:
     >We recently began using Adobe Photoshop to quantitate signals on 
     >Northern blots after we lost access to a densitometer.  We determined 
     >a range of total RNA loaded in which the signals from our mRNAs of 
     >interest were linear, and the data we obtained using the scanner + 
     >Photoshop agreed with our earlier densitometry data.  A colleague who 
     >used similar quantitation methods recently had problems with a 
     >reviewer who said this quantitation technique was not valid.
     >My question is: Can Photoshop validly be used to quantitate signals 
     >on autoradiographs?  If so, what conditions/guidelines must be 
     >followed?  Also, any relevent references would be appreciated.

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