Hey Newbies...Histogram 101

[R_Fredrick_Smith]

Originally Posted by PhotoDave1

Hi Guys:
Thanks for the primer on Histograms but I have to ask the question, what do I do with a Histogram and how do I use to adjust the settings on my camera to get better photos?
I used a Nikon D100 for a while before converting over to Canon (EOS 10D w/ Canon Lenses to be specific) and I had a heck of a time in getting the D100 to where I could get good, consistent photos out of it on a reliable and I am having the same problem with my EOS 10D. A lot of the photos I take with my 10D are either over or underexposed and I can't seem to be able to find the sweet spot and it is driving me crazy.
I have my EOS set up in a similar way to how I had my D100 set up: ISO 200, White Balance set to Cloudy, Exposure Compensation set to 1/2 stop negative (a digital camera acts like a film camera loaded with slide film and I find that a little underexposure yields better photos).
My question is once I look at a Histogram in the camera what do I do and how do I alter the settings (and more importantly, what settings do I alter) in my camera to give me better photos?
I am sure a lot of us have struggled with this at one time or another so the assistance of the group is greatly appreciated. Thanks!

First of all, in the brief tutorial above, I explained what to do. You need to take an exposure of a known target that fills the frame of your viewfinder. In my example I use a black/gray/white target. This will produce a histogram that is three spikes for a well exposed photo. The further to the right the three spikes are without clipping the right hand spike the more data you will have for the photo. So if you underexpose, you are doing exactly the opposite of what you need to do. Underexposure will move the three spikes left which means you are going to be losing shadow information. You need to slightly overexpose in some cases to force the histogram right.

Looking at the histogram in the camera of the the actual scene is not going to help you a lot. It may tell you if you're clipping hightlights or shadows, but in most cases you really can't tell. That's why you use a target. You can use just a gray card, and fill the viewfinder with it and shoot at what you think is the correct exposure. You'll see one spike. If its in the center, then you have exposed the card at 18% gray, which is where its supposed to be, generally. Now you adjust the exposure a bit depending on the predominate lightness or darkness of the main subject. The problem with just a gray card, is that you only get one spike, so you could still end up clipping either shadows or hightlights and not know it. The black/gray/white target gives you the extra info to really fine tune your exposures. Here is the sample photo again showing the target:



Notice where the spikes are. Suppose you did what you've been doing and underexpose. Where would that put the left spike (the shadow spike). It would shove it further to the left, and probablly clip it and thus you would lose shadow detail. Since digital is linear you have much less data for shadows than for highlights. Basically the first 1/5th of the right of the histogram represent half of all the data. The next 1/5th, half of what's left, and so forth. So for a 8 mp camera you ahve 4 mp in the first 1/5th on the right, 2mp in the next 1/5th, 1mp in the next 1/5th, .5 mp in the 4 1/5th and .25 mp in the last 1/5th. Suppose you then underexpose by 1/2 stop. What do you lose? well you've shoved the histogram left by 1/2 of one of those 1/5th areas, so you've just lost 2 mp from the first zone, 1 mp from the second zone, and so forth. What does that tell you?

One of the keys to really good digital photos is right on exposure. Sure, if you shoot RAW, you have a lot more room to play with and you can often recover and still get a good image. But think how much better the image would be if you had all the available data to play with.

Cheers,
rfs

[moscato_images]

I got this idea from someone else and decided to create my own version. It's a grey card with R,G,Y,B mixed at the four corners in a gradient that fades to 18% grey in the middle. Then, (especially with JPG) with the grey point eyedropper you can alter the overall color by clicking up and down the sides of the greycard to change the color. Good idea if you are not a RAW shooter. Try it out. Open Curves and click around the card with the grey eyedropper.



-joshua

[R_Fredrick_Smith]

Originally Posted by moscato_images

I got this idea from someone else and decided to create my own version. It's a grey card with R,G,Y,B mixed at the four corners in a gradient that fades to 18% grey in the middle. Then, (especially with JPG) with the grey point eyedropper you can alter the overall color by clicking up and down the sides of the greycard to change the color. Good idea if you are not a RAW shooter. Try it out. Open Curves and click around the card with the grey eyedropper.



-joshua

I guess I'm missing something based on your description and your photo. I don't see anything but gray, black and white in the card you're showing. Where is the R G and Y in the 4 corners?
In any event, the use of a card with black, gray and white will allow you to pretty much nail color balance using curves. You would normally use all three eyedroppers, however. You first use the black eyedropper and click on black, then the white eyedropper on white, and finally the gray eyedropper on gray. This will usually do the trick for JPG images.
Cheers,
rfs

[mickeyparris]

So, maybe I missed something in my readings here. Let's say I have a Canon 20D. What you guys are saying is to take a shot of a White/Grey/Black target, and then set my white balance to the target? Or is this whole thread about post shooting editing?

I'm sorry I'm stupid.

[R_Fredrick_Smith]

Originally Posted by mickeyparris

So, maybe I missed something in my readings here. Let's say I have a Canon 20D. What you guys are saying is to take a shot of a White/Grey/Black target, and then set my white balance to the target? Or is this whole thread about post shooting editing?
I'm sorry I'm stupid.

All of the above. I use the target to set precise exposure as described in my other posts. I also use the target to set a Custom White balance and the optimum photo fo the target is the reference on the 20D for that white balance. I normally shoot RAW, but if you are shooting JPG only, then you can use the photo that has the target in it to do post processing to correct for any color tints, etc.
Cheers,
rfs

[sculptor]

Lets assume you are not shooting raw (it makes the discussion more fun.) Now
there are three thing you can control to change the shape of the histogram.
They are exposure, contrast and lighting. One thing to keep in mind is the
amount of black shown on all histograms is constant so adjusting the three
variables above merely scoots the black stuff around or changes it shape.

Now a decent photo is not underexposed or overexposed. What this means in
terms of the histogram is that the black stuff is not trying to climb out of
your camera on the left or right sides respectively. So we can look at a
histogram and use the exposure controls on the camera to push that black stuff
back away from the edges so you can get a decent shot.

So you say to yourself can I use it to do better than just a decent shot?
Yes, and that where the other two variables come in. Imagine if we had a
histogram that was just a big glob of black right in the middle. What this
would mean is that out photo would look like it was of a grey cloud. Now if
you look at your typical boring washed-out looking photo it sort of resembles
that grey cloud I was just talking about doesn't it? What this means it we
need to spread that glob in the middle out so we have some dark tones
and some light tones and some interesting things in between. This spreading
things out is referred to as increasing the contrast. Some cameras have
controls to let you do this if your camera doesn't then just remember
Photoshop has histograms that work the same way as the on camera do!

Now you can also get some information about the lighting of your photo
by looking at the histogram. For instance you didn't light your background
sufficiently well there will be a mountain range over on the left of your
histogram. Now I've got to admit that histograms aren't the best tool to
do this kind of thing but they do reflect (no pun intended) your lighting.

Now none of this really matters all that much if you didn't light the face of
your model. So remember histograms are a tool and not a cure-all.

-- Gary
http://www.bronzedreams.com