Intensity Definition?

[Jason NoSpam]

Hi,

In ImageJ, is the image "Brightness" adjustment (Image menu -> Adjust -> Brightness/Contrast...) the same as adjusting an image "Intensity" in other imaging applications?

Thanks!

 
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[Jon Harman]

Hi,

Do you mean intensity in color photos?  For other digital images it
depends on the type of imaging sensor used and post processing of the
sensor data.
For 8 bit color RGB  ImageJ uses the Java awt.Color routines.  Java uses
HSV, with V=max(R,G,B).  Some other applications use HSL where L=
(max(R,G,B) + min(R,G,B))/2.

See http://www.easyrgb.com/math.php?MATH=M22#text22

In either case the number does not represent light intensity in digital
camera data.  The sensors in a camera do detect the intensity of the
(filtered) light that strikes them, but this is then manipulated (gamma
corrected) for better display on computer monitors.  The RGB values in a
jpg photo from a digital camera are usually gamma corrected.

I have run into some problems using the ImageJ "enhance contrast"
routine on an image with very bright colors. .  As you can see from the
definition of "V" there are lots of colors that map to the max V value.  
Perhaps a better choice would be the Y from YUV
colorspace.Y=.299R+.587G+.114B.

Jon




Jason NoSpam wrote:

> Hi,
>
> In ImageJ, is the image "Brightness" adjustment (Image menu -> Adjust -> Brightness/Contrast...) the same as adjusting an image "Intensity" in other imaging applications?
>
> Thanks!
>
>  
> ---------------------------------
> We have the perfect Group for you. Check out the handy changes to Yahoo! Groups.
>
>