How much latitude is in the Histograms range?

[rickm]

I've learned a bunch from everyone here on shooting "within" the histogram and thus preventing the clipping of highs & lows. Now I was wondering about how many stops there are between dark & light (left & right side)? I'm guessing about 2.5 but wanted to know if there is a postive answer to this or if it's still varible to certain conditions.

[Longwatcher]

I have read somewhere and my experience seems to back up that each line represents a full f-stop, thus a 10D histogram displays 5 f-stop range.

This seems to make sense from the aspect of playing I did this weekend, where it would go from one side to the other in about 5 f-stop equivilants.

Just my experience.

[rdenney]

rickm wrote:
I've learned a bunch from everyone here on shooting "within" the histogram and thus preventing the clipping of highs & lows. Now I was wondering about how many stops there are between dark & light (left & right side)? I'm guessing about 2.5 but wanted to know if there is a postive answer to this or if it's still varible to certain conditions.

The histogram shows the color 0,0,0 to 255, 255, 255, which is absolute black to absolute white. Anything falling off the end of the scale will be all zeroes or all 255's, and therefore impossible to render any other way. Trying to relate the histogram to stops is likely to introduce some unhappy non-linearities, so I think it's better to learn how to interpret it on its own by experimentation.

The determination of how many "stops" of scene luminance can be rendered between absolute black and absolute white is what you are asking, but the histogram provides no help here. I've seen tests that suggest this range is around 7.5 stops. If that range was narrower, more of the scene would fall off the edges of the histogram, and if wider, more of the scene would fall within it.

Rick "thinking the histogram shows information about the digital outcome, not about the scene itself" Denney

[kush]

Can anyone help with practical guidance on how to properly use the histogram in order to adjust the next shot to proper exposure. In other words, what do I look for in terms of the shape of the thing - my understanding is that a nice well balanced bell shape is what I want? What about the real intense spikes that you see sometimes, what do they indicate? What does the amplitude of the histogram bars tell me? Why is it that sometimes I get a real screwy 'gram, but the picture looks perfectly acceptable. If you guys have any advice or a helpful link that would be great.
(D10, 420ex, EF28-135 is)

many thanks in advance

kush "who thinks that there is no way in heck he could have stood a chance in beginning to learn this art of photography if it were not for digital"

[martcol]

I've always understood the histogram to be somewhat scene dependent. If you have a scene that is fairly even, nicely exposed you'll end up with a nice smooth hump. If the scene is full of extremes or very bright or dark the histogram will show peaks. If this is the case the histogram reading will be useful for comparing like scenes or different settings for the same scene.

Or.... I completely misunderstand histograms and could be getting more from them?

I regularly see histograms with my 10D that have no values at the extremes showing that all the pixels are grouped around the middle values. I usually find a levels adjustment in PS helps brighten the image. On a technical level: I haven't the faintest idea why!

Martin

[Jeppe]

Nonono.. there is no such thing as a perfect histogram. It just shows the amount of highlights, shadows and 18% grey and all those tones that are between.

Therfore a low-key scene (as a nightshot) will have all @ the left side, and a high-key (as a sunny beach) will have all or most at the right side (although, the camera will try and place the beach in 18% gray and thereby underexposing the scene).

The problem is when the curve doesnt seem to end where the histogram ends. Then you have either washed out highlights or very dark shadows.

A bell-shaped histogram just indicates that there are alot of middelgray tones in the picture (like taking a photo of a green lawn in hazy weather (just the grass)).

If you want to learn about histograms some more:

http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml

[pukkita]

There's about 5 to 6 f-stops in terms of luminosity.

There's no correct histogram. It only aids (and not always, as the histogram is luminosity, not each color channel based) to see if you exposed it right or not; it shouldn't be clipped (vertical values from top to bottom or next to the sides) and that's all.

Check the link Jeppe has suggested. And once you've understand it, check http://www.luminous-landscape.com/tutorials/expose-right.shtml for another aid histograms provide to minimize noise.