Posted by Mike Sellers on October 28, 2007 at 2:23 PM
What does the histogram look like on an ideal exposure? Is it supposed to be centered?
Posted by Rod Barbee on October 28, 2007 at 3:17 PM
The histogram is image dependent, there is no ideal histogram. If you have a scene with high contrast the histogram will show a spike of pixels somewhere on the left side in the dark area and another spike somewhere on the right side in the highlights area.
If you have an image that's overall monotone, like fog, you'll get a histogram that will have all the pixels bunched up in one area, typically the middle or to the right, depending on how you like to expose fog.
An image containing a lot of different tonalities from darks to lights will have a sort of humped shape all the way across.
I see too many people getting hung up on the "ideal" histogram. There is no such thing.
There are things to avoid like spikes at the far right (blown highlights) and far left (blocked shadows), but each histogram depends entirely on the scene in front of you and how you've exposed it.
If you get Outdoor Photographer, I wrote an article about histograms for the August 2006 issue that may help as well. I don't think they have that particular article posted on line but you can probably find it at a library.
Posted by Fred Stearns on October 28, 2007 at 7:14 PM
There is also an article in the current issue of Digital PhotoPro. This article is more geared for those who shoot in RAW. This article re-enforces what I have read in several places. If you are shooting in JPEG, you can probably use the histogram with worry. However, the histogram is from the JPEG conversion in the camera. This article implies that the camera creates a JPEG image when you view the picture. I have heard in other articles that there is a JPEG image embedded in the RAW images. I suspect the latter is true as the Epson P-2000 can view my RAW images without having a RAW converter. RAW handles the light differently than JPEG. I really don't understand it. However, when the histogram shows clipped highlights, they are not clipped in the RAW files and the detail can be recovered in processing if they aren't clipped too badly. I have tried this and found that, if I did not have too many "blinkies", I could recover the highlights.
Rod is definitely right in that there is no "Idea" histogram. My first scanner scanned every picture as if it were high noon. It must have been trying to achieve that "ideal" histogram. The results were terrible. Can you imagine a sunset shot corrected for high noon? I have no idea how PhotoShop treats the histograms. All I know is that it works. I wish that the camera vendors were a little more forthcoming with some of this information. They all do it the same, or so it seems, so there is nothing proprietary about this issue.
I wish you luck Mike. take a day and try different things and see how they look on the computer. Take notes, like I usually don't and regret it, so that you can tell what the different selections were. The little screen on the back of the camera is not a good place to make judgments of this kind. The Digital PhotoPro article evens says that, when shooting RAW, the best selection may look the worst on the camera back.
Posted by Daniel Moore on October 28, 2007 at 11:48 PM
Here is some sites that might help you out. They have pictures and examples.
Posted by Dan Borzynski on October 29, 2007 at 11:19 AM
Fred, I don't even want to think of what those scans looked like.
(assuming a proper exposure for the following)
You should see peaks in the histogram where the scene has proportionally more of a particular tone, when compared with the rest of the scene. Take a look at any of John Shaw's books, in particular his discussions on exposure. His books are really well written, even though most of them are film based.
With regards to a proper histogram, this is where some judgement of tomes in the scenes will help you. If you have a lot of light areas or highlights, you should see a peak at the right side of the histogram. Similarly, darks areas will produce a peak on the left.
A scene with both highlights and deep shadows will have peaks at both the left and right side (shoot in July at noon with a clear blue sky)
Suppose you have a closeup of your the palm of you hand. For most people, that is +1 on tonality. What you should be seeing in the histogram, if it is exposed correctly, is a peak between the middle and the far right of the x-axis.
Heavy fog in a forest will probably produce a peak around +1 and almost no pixels anywhere else. The fog will kill all contrast, lightning the dark areas and darkning the highlights.
A scene with no highlights or shadows but a wide range of tones should produce a fairly flat histogram.
As was said above, it really depends on the scene.
Posted by Rod Barbee on October 29, 2007 at 7:32 PM
Discussion
6 repliesIf you have an image that's overall monotone, like fog, you'll get a histogram that will have all the pixels bunched up in one area, typically the middle or to the right, depending on how you like to expose fog.
An image containing a lot of different tonalities from darks to lights will have a sort of humped shape all the way across.
I see too many people getting hung up on the "ideal" histogram. There is no such thing.
There are things to avoid like spikes at the far right (blown highlights) and far left (blocked shadows), but each histogram depends entirely on the scene in front of you and how you've exposed it.
If you get Outdoor Photographer, I wrote an article about histograms for the August 2006 issue that may help as well. I don't think they have that particular article posted on line but you can probably find it at a library.
Rod is definitely right in that there is no "Idea" histogram. My first scanner scanned every picture as if it were high noon. It must have been trying to achieve that "ideal" histogram. The results were terrible. Can you imagine a sunset shot corrected for high noon? I have no idea how PhotoShop treats the histograms. All I know is that it works. I wish that the camera vendors were a little more forthcoming with some of this information. They all do it the same, or so it seems, so there is nothing proprietary about this issue.
I wish you luck Mike. take a day and try different things and see how they look on the computer. Take notes, like I usually don't and regret it, so that you can tell what the different selections were. The little screen on the back of the camera is not a good place to make judgments of this kind. The Digital PhotoPro article evens says that, when shooting RAW, the best selection may look the worst on the camera back.
http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml
http://www.sphoto.com/techinfo/histograms/histograms.htm
http://www.cambridgeincolour.com/tutorials/histograms1.htm
(assuming a proper exposure for the following)
You should see peaks in the histogram where the scene has proportionally more of a particular tone, when compared with the rest of the scene. Take a look at any of John Shaw's books, in particular his discussions on exposure. His books are really well written, even though most of them are film based.
With regards to a proper histogram, this is where some judgement of tomes in the scenes will help you. If you have a lot of light areas or highlights, you should see a peak at the right side of the histogram. Similarly, darks areas will produce a peak on the left.
A scene with both highlights and deep shadows will have peaks at both the left and right side (shoot in July at noon with a clear blue sky)
Suppose you have a closeup of your the palm of you hand. For most people, that is +1 on tonality. What you should be seeing in the histogram, if it is exposed correctly, is a peak between the middle and the far right of the x-axis.
Heavy fog in a forest will probably produce a peak around +1 and almost no pixels anywhere else. The fog will kill all contrast, lightning the dark areas and darkning the highlights.
A scene with no highlights or shadows but a wide range of tones should produce a fairly flat histogram.
As was said above, it really depends on the scene.