Re: info on gamma / math feature in ImageJ

Posted by Stuart Anderson-3 on Aug 24, 2006; 9:49pm
URL: http://imagej.273.s1.nabble.com/Could-ImageJ-be-ported-to-a-Mobile-Phone-tp3701757p3701760.html

Never mind - it's right there in the online documentation...Sorry about that.

Quoting Stuart Anderson <[hidden email]>:

> Does anyone know where I might find information on the mathematics of the
> gamma
> correction tool in the ImageJ Math menu?
>
> I've been using the Plot Profile tool to produce spectral plots from images
> obtained by a USB camera that's part of a CD-based grating spectrometer.  The
>
> raw signals from the camera are linear at low intensities (doubling the light
>
> intensity produces a doubling of the signals), but quite non-linear at higher
>
> intensities.  I understood that a gamma correction might fix this roll-off,
> and
> it does help.  With my camera a gamma of 1.4 seems to be about right.  That
> is,
> after a gamma correction of 1.4 the Plot Profiles of the corrected images do
>
> double when the intensity is doubled.
>
> However, the odd thing is that the gamma process, applied to the image before
>
> the Plot Profile operation, yields results that are not one-to-one within the
>
> Profile.  That is, a given value in the Plot Profile of the unprocessed image
>
> can correspond to several different values in the Plot Profile of the gamma-
> processed image (including zero and non-zero values).  I can see how - since
> the
> gamma is applied to the image before the Plot Profile is calculated - this
> might
> be the case, especially if the gamma correction is different for each of the
> RGB
> components, but I'd like to understand this better than I do.
>
> So, if anyone knows where I can find documentation on what the ImageJ / gamma
>
> process does that would be very useful.
>
> Thanks - Stu
>

*************************************************
Stuart M. Anderson
Associate Professor of Physics
Augsburg College
2211 Riverside Avenue
Minneapolis, MN  55454

Tel: [phone]
Internet: [hidden email]

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