Re: Incorrect density values when quantifying PNG files exported from GIMP
Posted by
Gabriel Landini on
Nov 19, 2012; 12:40pm
URL: http://imagej.273.s1.nabble.com/Incorrect-density-values-when-quantifying-PNG-files-exported-from-GIMP-tp5000862p5000863.html
On Monday 19 Nov 2012 11:24:04 you wrote:
> I have been using ImageJ to quantify some images (western blot scans,
> grayscale). The blots were first scanned in JPG format, then were rotated
> and cropped using GIMP and finally exported from GIMP either in JPG or PNG
> format.
Jpegs (unless the non-lossy version) for imaging are a very bad idea. There
are non-lossy formats (like TIFF or PNG) that retain all the scanned
information.
If you load the jpeg to rotate it and save it again in jpeg, you get more lost
information. Once saved in jpeg, there is no benefit in converting to PNG, as
the loss of information already took place.
It would be better to scan directly to TIFF, then load in IJ and use the
Image>Transform menu entry to rotate it (no need for the GIMP step).
It is also necessary to calibrate the scanner too, otherwise the meaning of
the darkness in terms of optical density units is unknown.
Regards
Gabriel
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