Histogram?

[dennykyser]

I see alot mentioned about histogram, I am completly lost here can someone tell me where I can learn about and learn to use this tool?

[robertwgross]

The manual does not tell you much on page 109.

A theoretically normal image should give you a bell-shaped curve, but few images actually look that way. A theoretically perfectly exposed image should be centered in on the mid-line, but it is quite normal for them to be off a bit.

If all you get is a big line on the far left, then it is probably seriously underexposed. If all you get is a big line on the far right, then it is probably seriously overexposed.

That is where the theory ends. There are many mood effects that you might be seeking, so you may get histograms that violate the normal rules.

---Bob Gross---

[Jim_T]

Here's a fairly good tutorial..

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

[where1]

Thanks Jim, that link helps me alot. I never used the histogram because of my ignorance of it, now I can turn it on and see how I'm doing.

[timmyquest]

Thanks Jim, that link helps me alot. I never used the histogram because of my ignorance of it, now I can turn it on and see how I'm doing.

I'm guessing you didnt read your manual...

[G3]

The Histogram is your best guide to how accurate your exposures are. You should set your camera so that it displays alongside your preview and learn to read it. The combination of the preview and Histogram will very accurately tell you how to set exposure.

The Histogram is a representation of what colors (tonal values) are present in your exposure and how much of the exposure is in those colors. The color is the horizontal axis. Black is represented all the way to the left and is assigned the number 0, white is all the way to the right and is assigned the number 255, with middle gray being in the middle and 128. How much of a particular color is in the image is shown by the vertical axis. The taller the peak at a particular coloron the horizontal axis, the more of that color is in the image. So, if you have an image where the Histogram is jammed up all the way against the left, and there is empty space to the right, the image is underexposed. Conversely, if you have one that is all the way to the right with blank space to the left, the image is overexposed and the highlight will be washed out.

This is a little deceptive though, fo a couple of reasons. First, if you have subject matter that is predominately black, your Histogram may look like your image is under exposed, and the opposite is true if you have predominately white subject matter, even if the exposure is actually correct. It takes a little practice reading exposures of this type.

Secondly, the available colors shown in the Histogram are not exactly linear. Let's establish two pieces of information first about the way a digital camera records the image. First, an image sensor has a dynamic range of a little of 5 f-stops. Second, the data is recorded in a 16-bit format, but only 12 bits are actually used. If you divide the Histogram into 5 (for 5 f-stops range) sections, staring from the left and going from 0 to 8, 9 to 32, 33 to 64, 65 to 128, 129 to 255 you will get a more accurate idea of how the colors are actually distibuted across the Histogram. From that you can see that about half of the available color information is in the right handmost (white) section from 129 to 255. An image sensor is capable of recording (with 12 bits to work with) 4,096 tonal values. The white section of the Histogram (129 to 255) actually contains half of the total tonal values. This is easier to understand if you remember that we divided the Histogram into 5 sections because that's how many f-stops of tonal range you have to work with. Remember also, that each f-stop represents a doubling of the amount of light. So, if you start from the left section (black, or 0 to 8 ), then move to the right to the next section (9 to 32) you double the amount of light again. By the time you get to the rightmost section (white or 129 to 256), you have doubled the light 4 times. That's why there's half of the total available data in that rightmost section.

What all of that means is that by exposing so that your Histogram is more to the right side, you actually capture more information. The image may look a little overexposed when you first load it, but it is easily correctable and you have more data to work with. If you expose more to the left of the Histogram, all that data was never recorded. It is possible to go so far to the right that all highlights are oversaturated and blown out, so you have to be a little careful.

This is all useful only if you do post processing in Photoshop or some other similar program. It also works better if you shoot in RAW mode and use the AdobeRGB colorspace. Photoshop CS even makes this better by giving you more capability of working in 16-bit mode.

[Scottes]

I'm guessing you didnt read your manual...

ROFLMAO

[billhercus]

Thanks G3. What a first class, compact, understandable explanation.

Keep ,em coming!!

Bill

[Morden]

Thanks G3. What a first class, compact, understandable explanation.l
Indeed. That description makes a good deal of sense.

[G3]

Thanks G3. What a first class, compact, understandable explanation.

Keep ,em coming!!

Bill

Glad it helped, Bill. Just remember the Histogram is a guide and is there to help you in-camera with determining exposure and in post-processing with measuring how your corrections are affecting the image. You shouldn't get so caught up in the Histogram that you ignore how the image actually looks. After all, you will sell the image, not the Histogram.

[scottbergerphoto]

This issue of exposing to the right and the distribution of tones on a histogram is covered very thoroughly at : http://luminous-landscape.com/tutorials/expose-right.shtml
Scott

[where1]

Thanks G3 for the explanation. I am still trying to digest it.

Thanks timmy for assuming I am smart enough to not need the manual. You are mistaken though, I do read the thing. I didn't know much about the camera's operation when I bought it. I read a section and try to understand it and apply it to the camera, most times I have to do this more than once. It sure is nice when someone like Jim_T, G3 or scottbergerphoto helps with sections I don't understand.

[G3]

Yep, reading the manuals can be some pretty doggone dry reading. Tough to stay awake and understand what you are reading. Usually someone on the forum can sort of condense it down to a semi-plain language explanation.

The Histogram looks much, much scarier than it is. Once you look at a few of them and compare them to the images they represent, it begins to make more sense.

One thing that will help you more than anything else is to take photo and bring it up in Photoshop or whatever program you are using and just start making adjustments and watching the changes to the Histogram. Experiment with Curves and Levels. Make sure you are using a copy of your original image so you don't inadvertently make unwanted changes to your image.

Watch what happens to the Histogram as you adjust the image (you may need to refresh it after the adjustment). If you are using Photoshop CS, experiment both in 8 bit and 16 bit mode. You will see that sometimes as you make extreme adjustments, gaps will show up in the Histogram. This means that you are losing information. You will also see that it tends to be much less severe in 16 bit mode. That is because you have more information to work with.

Also, experiment with the in-camera Histogram. Make an exposure at the camera's recommended settings, then make one a couple of stops underexposed and one a couple of stops overexposed and look at the differences in the images and the Histograms. You are shooting digital, so you don't have to worry about wasting film...you can simply delete your experiments when you are finished with them.

[maderito]

You are shooting digital, so you don't have to worry about wasting film...you can simply delete your experiments when you are finished with them.
I once read a post on some forum which went something like: "I've learned more in one month of digital photography than I have in 30 years of film photography."

Perhaps an exaggeration - but it rings true for me because we now have to guide our learning:
Instant feedback on exposure via histograms
Instant feedback on composition via on camera LCD image review
Instant feedback on "developing" via imaging editing apps like Photoshop.
The art of the shooting has always combined an intuitive feel for composition, exposure, and developing/printing. But as we become mesmerized by the technology of mastering the digital approach to these elements, we risk losing the art. That said, we must master the technical details just like a classic B+W photography mastered his/her knowledge of the zone system, chemicals and film emulsions.

Thanks G3 for getting us up to speed on exposure and histograms. It is fundamental and indespensible to our digital photo work.