[Cin] Histogram Plugin add on feature

Good Guy good1.2guy at gmail.com
Sun Sep 27 22:07:38 CEST 2020

The reason for the different appearance in the histogram displays is that
value used in each case is not really the same kind of answer.  A histogram
is a bunch of "bins" (accumulators) that count the number of times a
pixel channel intensity occurs in an image. Dim are on the left, bright on
the right.

The number of bins used depends on the color model bit depth,
histogram: 256 for rgb8 and 65536 for all others.
bezier: 256 for rgb8/yuv8 and 65536 for all others.
scope: always uses 65536

All of the bins are scanned when the graph is plotted.  What is shown
on which plugin is used.
histogram: was max of the bins in the pixel range, now is the sum
bezier: is the max of the bins in the pixel range
scope: is the max of the bins in the pixel range

When the color space and the bin size are the same, all of the values
the indexed bins.  When the color is the result of yuv->rgb conversion, the
"spread" if there are more bins than colors.  This is the same effect you
see when
you turn on "smoothing" in the vectorscope histogram.

The "total" pixels for each value is approximately the same, but the "max"
depends on the color quantization.  More colors increment more bins.  Fewer
colors increment fewer bins.  In both cases, the image size has the same
of pixels.  The fewer color case increments the used bins, and skips the
bins.  This sums all of the pixels into fewer bins, and the bins have
higher values.
That is the "rgb" vs "yuv" case, fewer vs more bins are used.

To report something more consistent, I have changed the reported value to
"sum" of the accumulated counts for the bins reporting a pixel bar on the
The effect of this is to do this:

   1                      1
000100 3 pixels   vs   0011000  3 pixels

On the left, the course color model piles all 3 pixels into one bin.  max
value 3
On the right, the fine color model puts the counts into 2 bins, max 2, sum 3

So, by reporting the sum the shape of the results are more similar.


On Sun, Sep 27, 2020 at 4:02 AM Igor BEGHETTO via Cin <
cin at lists.cinelerra-gg.org> wrote:

> Thanks Phyllis for your tests and GG for looking for.
> I don't think you are misunderstanding.
> I saw your video. I think it depends a bit from the video you are using
> for the test: your clip is an animation. I can wrong. In your screencast
> the histogram, in the Histogram Bezier, changes very, very, little.
> Please, take a look at my screencast: https://streamable.com/3svwkd
> As you can see, the histogram, in the Histogram Bezier, doesn't change
> as in the Histogram.
> More, you can see that when I enable the Histogram Bezier plugin a
> little change occurs in the histogram of the View Scope. Mmh, very
> strange. It is like if Histogram Bezier changes the Color Model of the
> project, but I am guessing.
> I am not saying it is "wrong", I think that it is really weird that
> tools that perform the same function (draw an histogram) don't show the
> same output, I would think.
> IgorBeg
> Il 27/09/2020 03:05, Phyllis Smith via Cin ha scritto:
> > IgorBeg,
> > GG thoroughly reviewed the Histogram code to understand how it works
> > so he could find any bugs.  He says it is all working correctly as far
> > as he can tell.
> >
> > But about the following:
> >
> >     When the Color Model format (in Settings->Format...) is set to RGB[A]
> >     the histogram displayed on Histogram plugins is the same as on
> >     Histogram
> >     Bezier plugin.
> >     If you change Color Model format from RGB[A] to YUV[A] the
> >     histogram on
> >     Histogram Bezier no changes, but on Histogram plugin and on View
> >     Scopes
> >     it changes. It is strange, I think.
> >     In Histogram Bezier plugin the histogram doesn't change in the
> >     differents color model.
> >
> > we see in https://streamable.com/vr5srs   that Histogram Bezier DOES
> > CHANGE between the formats of RGBA and YUVA (note that I have set the
> > slider all the way to Log in order to compare the same thing).  You
> > have to watch the Histogram Bezier graph specifically, but you
> > definitely see it change.  If I am misunderstanding the concern,
> > please let me know.
> --
> Cin mailing list
> Cin at lists.cinelerra-gg.org
> https://lists.cinelerra-gg.org/mailman/listinfo/cin
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