Interpreting Histogram Information

I've gotten pretty good at using the histogram to determine correct exposures and making adjustments to reduce noise, etc..

Sometimes I notice that there is a chunk of the histogram that spikes and is at the top, completely flattened out, and at times this section can span 1 whole region (not sure what they are called) on the histogram. What does this indicate and what, if anything do you to to correct it?

It shows the ratios of light and dark, from white to black, in a bell curve format. this all depends on the data in the picture. Go here it is a nice job on this issue. http://www.naturescape​s.net/092004/gd0904.ht​m

I've been researching this to figure out how to say it and came up with one of my favorite sites: http://www.luminous-landscape.com …standing-histograms.shtml

Dante's site looks pretty good too. Basically you are looking at a graph indicating the distribution of luminance across the dynamic range. I think.

I do understand that and have read many of the links about histograms but I am still unclear about what it means when there is a chunk that is flattened at the top and the dynamic range is evenly distributed.

I would interpret it as meaning the majority of pixels in the image were concentrated in that zone of the exposure. Can you post and example with the picture?

Information about the Histogram, Fantastic.
I always thought it used up battery and turned it off.

Good tutorial
http://luminous-landscape.com …standing-histograms.shtml

Transportithere wrote in post #2283647
Information about the Histogram, Fantastic.
I always thought it used up battery and turned it off.

You're kidding, right?

A large range that is flattened at the top would indicate an area of the picture where there was a gradual and even transition from dark to light. For example, if you used a light that had a soft edge and placed the edge so that it illuminated a flat area, you'd get that kind of histogram. Another way to achieve that result would be to use a flash to light up a wall that was running almost directly away from you.

As long as the shot looks good, I wouldn't worry too much about it.

Titus213 wrote in post #2283677
You're kidding, right?

I hope so.

Mind you, using it does use battery power , ...along with autofocus and metering...

gkuenning wrote in post #2283757
A large range that is flattened at the top would indicate an area of the picture where there was a gradual and even transition from dark to light. For example, if you used a light that had a soft edge and placed the edge so that it illuminated a flat area, you'd get that kind of histogram. Another way to achieve that result would be to use a flash to light up a wall that was running almost directly away from you.

As long as the shot looks good, I wouldn't worry too much about it.

I thought that a flat top on a histogram spike simply indicated that a lot of pixels captured information at that particular dynamic level, and that the information is there, but simply can't be charted on the limited vertical range of the histogram.

In the Luminous Landscape tutorial, there is a shot of the full moon - most of the picture area is very dark, and there is one chopped off spike at this dynamic level (near the left, but not totally black). Although most of the picture is dark, some detail can be seen - if the spike was jammed to the left, not much detail would be discernible.

For instance, here is a pic I took looking out a window and just working on metering and exposures.

What does the spike represent?

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TMR Design wrote in post #2285558
For instance, here is a pic I took looking out a window and just working on metering and exposures.

What does the spike represent?

I'd say that the middle 'spike' is the wall and the right hand 'spike' is the sky

kevin_c wrote in post #2285567
I'd say that the middle 'spike' is the wall and the right hand 'spike' is the sky

I would say exactly the same thing.

And there is simply too much data in the same tonal range for it all to fit on the histograms Y axis. Its my understanding that this dosn't matter, it has no effect on the image, and simply tells you that have a lot of data covering the same, or similar tonal range.

That's interesting. I guess that implies that the vertical axis (amount of pixels) is less than the total pixel count of the sensor, and therefore once a certain number of pixels with the same tonal range exceeds the axis the histogram peaks 'off the chart'.

I wonder if it's possible, or useful even, for cameras' onboard computers to dynamically scale the histogram so that all its pixels show on the chart even if the entire frame is filled with just one tone. Perhaps we can even experiment with different camera models with same sensor size to see if the max pixels on the vertical axis is constant.