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Old 06-18-2007   #21
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Default Re: Histograms???

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Originally Posted by obtr32 View Post
Sooooooo.....the bottom line is....don't worry about it?
...unless you are a fashion shooter that needs all the colour info he/she can get to get the latest fashion colour 'A- OK- 100%' in his/her prints...

...what you do is NOT blowing highlights or blocking shadows, *I* learned the term 'clipping colours' for the phenomena that you have 'cut off mountains in the middle of your Histo'

IIRC what-you-loose is some graduation(s) of colour(s), the 'gradual toning' becomes a little less...

...and a nice read...



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Old 06-18-2007   #22
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I have read through this post and am a little confused on histograms...now. It was my understanding that the historgram was not a static graph. The top line is determined by the height of the pixels with the greatest number of occurrence. For example, if a midtone had 130 pixels, and that was the highest pixel count for that image, then the top of the histogram would read 130 pixels. If the highest pixel count was 580 then the top of the histogram would be at 580.

Correct me if I am wrong, but I have heard this explanation from a couple of sources. Tonal quality is determined not so much by the height of the pixels, but by the overall position of the "hump" for lack of a better term.
Kelly,

Don't be confused by the somewhat conflicting (or confusing) statements in this thread. You have got it absolutely correct. The Y axis (pixel count) of a histogram is constructed on a relative scale with the tonal value having the highest pixel count being used as full scale and all other values are graphed relative to that. Therefore no Y value can go off the scale.

The position of the "hump" is simply indicative of the majority of tones in the image, and this will naturally vary depending on the subject and lighting.

Cheers/Mike
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Old 06-18-2007   #23
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There is no ideal histogram shape. It is a function of the composition. If the comp is very dark, then it is not wrong that the histogram shows an "out of balance" shape, in regard to shadows versus highlight. The biggest mistake people make is that they try for a particular histogram shape.

The X axis is absolute, but the Y axis is more scalar. The Y has no "blown" limits, but the X does.
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Old 06-18-2007   #24
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Default Re: Histograms???

Quote:
Originally Posted by Max@Home View Post
...unless you are a fashion shooter that needs all the colour info he/she can get to get the latest fashion colour 'A- OK- 100%' in his/her prints...

...what you do is NOT blowing highlights or blocking shadows, *I* learned the term 'clipping colours' for the phenomena that you have 'cut off mountains in the middle of your Histo'

IIRC what-you-loose is some graduation(s) of colour(s), the 'gradual toning' becomes a little less...

...and a nice read...



Max@Home
Max,
Agree that the Cambridge article is very informative and points out the difference between a RGB and Luminance Histogram.

A minor disagreement with your statement above that color clipping is indicated by "cut off mountains in the middle of your Histogram". Color clipping, as the cited article points out, is seen when viewing the individual color histograms and is indicated by a spike at the extreme right of the color curve where clipping occurs. Indeed, when this happens you may loose the subtle gradations in the tones of that color.

Cheers/Mike
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Old 06-18-2007   #25
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Default Re: Histograms???

Mike,

I tried to 'keep it a little simple' , but your explanation is the better one

...thanks for the improvements, I bow for thee and salute thee



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Old 06-18-2007   #26
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Default Re: Histograms???

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Mike,

I tried to 'keep it a little simple' , but your explanation is the better one

...thanks for the improvements, I bow for thee and salute thee



Max@Home
Thank you Max. A bow and a salute are real compliments coming from you; I am flattered.

Since this thread deals with in camera histograms, let me air something that confounds me. No camera manufacturer that I know of bothers to explain what type of histogram is displayed on camera (luminance or rgb). Furthermore it is nowhere specified how the X (tone) axis is constructed. Is it linear or logarithmic? This is of some consequence when one is attempting to get the maximum information from the sensor by "Exposing to the Right". I am aware that the displayed histogram is a melange of information derived from the in camera conversion to a jpeg with all the associated "adjustments" and, by itself, may not be all that informative. My approach to this problem is to keep moving the histogram (by varying exposure) and observe the results in the final image after raw conversion. Eventually one gets a feel for it.

Cheers/Mike
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Old 06-18-2007   #27
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Default Re: Histograms???

Pauly,

As far as the spike reacing the top of the historgram, that is correct. Don't worry about it. You will always have a spike reaching the top of the histogram, regardless of the scene or the exposure. Worry about the left and right. But also learn to read a histogram based on the scene you are shooting.

I am very happy with the exposure on this image. But there is a lot of black in the image, therefore, I would expect more black and darker toned images than any other. It does not bother me that the blacks reach to the top of the histogram...it concerns me more that they are clipped on the left side of the histogram. That is where the major concern should be...left side/right side.

You will also notice that because there are so many black pixels that all of the other tones look rather flat. They are rather flat looking ONLY because there are so many dark pixels. When I isolate the subject in PS and take away the black background, I get a relatively nice looking histogram. Oddly, something very light in tonal value reaches the top of the histogram in the isoloated sujbect reading. Anyway, the fact is, histograms change depending upon the picture. If in this picture I did not have a distribution of pixels along the X axis, I would be concerned. The height of the distrubtion relative to the tall darker value spikes is going to be rather short because of all of the black in the scene.
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Old 06-18-2007   #28
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Absolutely right and beautiful image Kelly.



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Old 06-18-2007   #29
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Thanks Julio. I was very pleased with the way these came out. They were from my daugther's high school play. Shooting stage shots, for me, is tricky. I spot metered for what I thought was the brightest spot on the stage and shot from there. Early in my Camel career, I shot a wedding full of black tuxes and YUCK! Now, I think I could do it with greater confidence.

What kind of hat are you wearing in that picture? (Digression.) Almost looks like a tri cornered hat.
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Old 06-19-2007   #30
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hehe.. It's a Colombia boonie hat.

The shot was from a trip I took with the family to Metro Zoo in Miami. My son had his coolpix camera and shot a picture of me. He was proud of his picture so I used it here. He was thrilled.

I got a wonderful shot of the kids feeding the giraffes. They set up a ramp and kids get to go up, hold out some branches and the giraffes come up and eat the leaves off the branches you are holding. What a thrill to feed a giraffe. They loved it.


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