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histogram clipping
show user profile  Setherial
Hey guys

Question about histograms and clipping. I understand the histogram left to right and dataloss when either side is clipped but what is happening when you have a peak somewhere in the middle of your histogram that is clipped at the top? Is that a problem, is there a problem with exposure or what. I noticed it the other day when shooting and can't find any info on the subject.



read 591 times
7/27/2014 10:09:47 AM (last edit: 7/27/2014 10:10:34 AM)
show user profile  moid1111
A practical example:

1-Let's imagine there is 100 pexils in the screen from pexil1 to pexil 100

2-And this histogram was representing white and black value from 1 to 0 in these pexils.

3-and pexils from 20 to 80 have value of 1, and the other pexils have values less than 0.5.

4-experiment (i) clipping from right until pexil 81 , results in values of the pexils 81 and above to
Change from eg, 0.46 or 0.1or, 0.98 to 1.0 which means the screen becomes whiter.

5-experiment (ii) clipping from left until pexil 19, results in values of the pexils 19 and below to
Change from eg, 0.46 or 0.1or, 0.98 to 0.0 which means the screen becomes less whiter .

6-experiment (iii) which is the question is about it,
Clipping from the top which means pixels having a value of 1.0 would have less value, they would
Have a value of 0.7 as an example, so pixels that is above 0.7 will set at 0.7, pixels from 20 to 80"
And so these pixels become less whiter.

There is many types of histograms , for blue , red , white ...

read 580 times
7/27/2014 12:25:00 PM (last edit: 7/27/2014 12:39:31 PM)
show user profile  Setherial
I don't think I understood much of that

what I mean was this

what does the graph indicate when it hits the top like that?
read 569 times
7/27/2014 1:48:50 PM (last edit: 7/27/2014 1:48:50 PM)
show user profile  moid1111

The peak on the righ says there's areas"pixels" that have very high value of white, in
Another word its very exposed, as in the street of this photo,

The horizontal line represents pixels that start as black and until the right end as white,

So, the left peak which is situated in the left area, which is very high, meaning there is some area
In the photo that is underexposed as you can see near the Window,
And as you can see from the histogram, there is no high values in the black side
Except that peak.

Histogram is something like a black white gradient, the higher or lower value in any region, of this gradient.
Reflected in the photo, as dark or not dark area , so try to have over exposed photo
You would notice, there only peaks in the right side of the histogram...

And please correct if something I mentioned isn't accurate.

read 565 times
7/27/2014 3:39:35 PM (last edit: 7/27/2014 3:39:35 PM)
show user profile  Setherial
doesn't the vertical axis represent how much there is of something, if it's flat you don't have anything in that particular value range in your image. Loss of detail occurs when there is detail either at the right edge of the garph (white's are blown out, overexposed shot) or at the left side of the curve (loss of detail in the blacks, underexposed shot). But my peak is in the mid tones, is there loss of detail there or does it just indicate that there's lots going on in that value range and that's it?
read 561 times
7/27/2014 3:55:20 PM (last edit: 7/27/2014 3:55:20 PM)
show user profile  BishBashRoss
Hi Seth. I wondered about this myself recently too. I came to the conclusion that it's not an issue and like you say just means there's lots of data in that tonal range.

read 558 times
7/27/2014 4:00:09 PM (last edit: 7/27/2014 4:00:09 PM)
show user profile  Setherial
Drives me crazy that when you google it they explain the X axis but not the Y axis, but apparently If I'm not mistaken the X axis is like we all know the value scale from black to white and represents the tonal range of your image, high key has lots to the right, low key lots to the left but in the end it doesn't matter as long as you don't lose detail by over or in lesser degree under exposing.

The Y axis represents the the color or in a black and white histogram the value representation of the color from 0 to max whatever your color range is, in an 8 bit system that would be 0 to 255. being at the 255 end of that doesn't mean there is anything wrong with your image, it's just a bright value. Also I vaguely remember the histogram always being calculated on a jpg representation of your shot (not on RAW) so I guess it's always 8 bit.

That also explains why RGB histograms peak at a different position on the tonal (X-axis) scale, as differnt colors have different values at their maximum chroma.
read 552 times
7/27/2014 4:33:54 PM (last edit: 7/27/2014 4:33:54 PM)
show user profile  BishBashRoss
Perhaps I'm miss interpreting you but that's not how I understand the Y axis to work. My interpretation is the y axis represents the number of pixels at that tonal range.

read 542 times
7/27/2014 6:32:30 PM (last edit: 7/27/2014 6:32:42 PM)
show user profile  Setherial
pixels are present everywhere it's the value they store that can differ (being a value from 0-255) so what you say doesn't really make sense
read 533 times
7/27/2014 8:57:21 PM (last edit: 7/27/2014 8:57:21 PM)
show user profile  moid1111
The value is not from 0 to 255,
But from 0 to 1
How much white is, 60% 0.6, 90%, 0.9 ....

About mid tones

Imagine all tones in the photo are from 1 to 100, the horizontal line.

So tone 1 is pure black , tone 100 is pure white,

Mid tones are from 2 to 99

Imagine that the vertical value of the tone 30 to 80 is 1.0
What does that means?

Does it means its white imagine?

No, only mid tones are intense, so the image would look gray.

It depends on which tone are high ,
Are they the tones near black, white, or both, or...

read 526 times
7/27/2014 10:20:59 PM (last edit: 7/27/2014 10:20:59 PM)
show user profile  moid1111
Yes, pixels have information not just about color,

I was wrong, it's simpler to use the term tones , than pixel.
But these tones reflected in these pixels.
read 526 times
7/27/2014 10:30:48 PM (last edit: 7/27/2014 10:30:48 PM)
show user profile  reeves1984
X axis is the RGB value, Y value is the number of pixels. Even wiki says so.

' does it just indicate that there's lots going on in that value range and that's it?'


Vectorscopes is where it gets more interesting, they they are plotted based on screen position and stuff.

Simon Reeves - VFX Artist & Blog
twitter <-- I work here

read 523 times
7/27/2014 10:46:04 PM (last edit: 7/27/2014 10:46:04 PM)
show user profile  moid1111

cool reeve!

read 517 times
7/28/2014 1:19:55 AM (last edit: 7/28/2014 1:19:55 AM)
show user profile  Error404
yea, I don't think it means anything is clipping. -

read 509 times
7/28/2014 6:24:04 AM (last edit: 7/28/2014 6:24:04 AM)
show user profile  Setherial
ok thanks guys, I think I understand it well enough now to put it to use
read 500 times
7/28/2014 9:28:33 AM (last edit: 7/28/2014 9:28:33 AM)
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