Hi Andre,
for color images, the "standard" histogram display depends on the
setting of Edit>Options>Conversions>Weighted RGB Conversions.
If this option is on, the intensity on the x axis of the histogram plot
is calculated as 0.299*R + 0.587*G + 0.114*B and labelled "Intensity
(weighted)".
If "Weighted RGB Conversions" is off, the intensity is calculated as (R
+ G + B)/3, and labelled "Intensity (unweighted)".
In "R+G+B" mode, the histogram shown is the sum of the histogram of the
histograms of the individual channels, i.e., the value for intensity 0
is the sum of the number of pixels where R=0 plus the number of pixels
with G=0, plus the number of pixels with B=0. You will also see that the
number 'N' of intensity values examined is three times as much as the
number of pixels.
If you want to examine bleaching, you are probably interested in color
saturation, so you could convert the image to a HSB stack and look at
the saturation and its histogram.
There are also nice plugins for color inspection, e.g. the 3D Color
Inspector/Color Histogram by Kai Uwe Barthel
https://imagej.net/ij/plugins/color-inspector.html
Of course, you have to make sure that illumination conditions and white
balance of the camera are always the same. Accurate color measurements
are a science on its own...
Michael
________________________________________________________________
On 27.02.24 19:53, Andre Briscoe wrote:
Hello,
I am currently working on designing a method to use ImageJ to estimate
bleaching in corals using the histogram function and was wondering what is
being represented in the R+G+B graph in case it is the graph best suited for
what I am trying to do. Does anyone happen to know?
Best,
Andre Briscoe
PhD Student
NSF CREST Center for Aquatic Chemistry and Environment
Institute of Environment, an FIU Preeminent Program
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