The reason for the different appearance in the histogram displays is that the
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 particular
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 depends
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 increment
the indexed bins. When the color is the result of yuv->rgb conversion, the results
"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" value
depends on the color quantization. More colors increment more bins. Fewer
colors increment fewer bins. In both cases, the image size has the same number
of pixels. The fewer color case increments the used bins, and skips the unused
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 the
"sum" of the accumulated counts for the bins reporting a pixel bar on the graph.
The effect of this is to do this:
1
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.
gg