
Understanding image histograms with OpenCV - se7entyse7en
http://lmcaraig.com/image-histograms-histograms-equalization-and-histograms-comparison/
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platz
> In the case of 2D histograms the resulting plot will have the pixel
> intensities of a channel on the X-axis, the pixel intensities of another
> channel on the Y-axis, and the frequency is given by the color of the plot.

I'm still having a hard time understanding what exactly this represents and
how to properly interpret it.

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joshvm
There's a nice overview here:
[https://svi.nl/TwoChannelHistogram](https://svi.nl/TwoChannelHistogram)

I don't know any professional photographers who use 2D histograms for editing,
or whether you can actually plot them in Lightroom or Photoshop. However for
scientific image processing it seems to be more useful.

OpenCV also has a tutorial:
[https://docs.opencv.org/3.3.1/dd/d0d/tutorial_py_2d_histogra...](https://docs.opencv.org/3.3.1/dd/d0d/tutorial_py_2d_histogram.html)

But which of the 'coming chapters' it's referencing I have no idea.

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pmoriarty
_" We can easily extend what we've done for the 2D histogram to calculate 3D
histogram... Unfortunately we cannot visualize this histogram."_

Why not? Couldn't you just create a 3D image?

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nerdponx
You would only be able to see the outside "shell" of it.

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pmoriarty
There are visualization programs that will let you move through a 3D volume,
slice by slice, as it were (along various axis). So this shouldn't be an
issue.

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ascorbic
It wouldn't be a 3D volume though. A 2D histogram is a 3D volume. A 3D
histogram would require a 4D object, so it would be a case of "first build
your hypercube..."

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akx
How about a 3D point cloud with dot size corresponding to intensity?

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Franciscouzo
Something like this [0]? (Disclaimer, I made it)

[0]
[https://franciscouzo.github.io/image_colors/](https://franciscouzo.github.io/image_colors/)

