A balance image is an image that the content of the histogram are filling up the middle area - not too right or not too left. To be noted that this is not the end product that we try to achieve after processing, this is only a guide to ensure that you can preserve as much detail as possible when taking a shot. You may need either to put histogram display on your camera live screen, or observe them once you finish pressing the shutter - to ensure that the pixels spread are across the middle area so you can get an acceptable amount of details for better processing.
The foreground is not too dark and the background is well lit. This is a sample of exposure-balanced shot where you can see on the histogram that the midtone / middle part is filled proportionally and there is nothing that comes too much on the edge of histogram.
Reveal the histogram display on the camera live screen so you can observe how it looks before pressing the shutter.
Avoid of taking a shot if the graph is filling up the edge of the histogram - creating a highlight / shadow clipping. Clipping means that the detail of the image is already lost since that area is way too under / over-exposed. This is why histogram is essential so you don't need to face this pixel lost issue during post processing.
Using RAW editor, you can spot where the clipping area are by clicking the top-right button on histogram. The pixels marked by red area shown there are damaged already and for most of the time, it couldn't be retrieved anymore.
Shadow clipping is shown on the blue mark shown on several small part within the above image. Same goes with highlight clipping, this dark part has lost the pixel details so it can be considered damaged & should be avoided whenever possible.
Shot RAW so you can easily adjust the shadow / highlight contents without damaging the shot. This step is strongly related with the next one as sometimes the existing shooting condition is not so favourable for getting a balance capture.
When the condition does not allow you to take a kind of balance shot (where the graph is dominant on the middle part), it is still okay to have a slightly left or right graph as you can repair it later during post processing - especially if you are shooting with RAW file. RAW editor software is usually available for free from camera manufacture software & you may see how it gives you a lot of advantages for repairing your shot by looking at below examples.
This is a sample of underexposed shot that I need to take because I want to get a good sky details. The foreground is too dark but I know by looking at the histogram, that this image still possess good pixel data as there is no clipping occurred on this shot.
Only by using a slider from RAW editor, I can significantly repair the exposure & make it looks nicer and balanced. Since all the adjustments were done on the RAW file, so I didn't make any harmful modification on the image and that's why getting a capture on RAW format is a must!
Sometimes when you take a shot at noon time, the environment is too bright for you to have a review of your images in camera screen. I find histogram helps me to determine whether my shot is already balanced or not eventhough I couldn't see the image clearly due to harsh sunlight. This is another important part on how observing an image's histogram can improve your overall shot quality.
Besides taking a shot in RAW format, I found that a regular observation on the image's histogram is another most important thing to ensure that the shots you take are within your expectation. No photographers want to get a surprise when they are checking the images on their home because an unnoticeable clipping that is hardly seen on camera screen. And histogram is a very reliable tool to ensure that you can obtain high quality resource for your next processing workflow.
Pro photographers do not only have a good eyes and taste while crafting a shot, but they also put a great attention on the details to ensure its quality. Here, I will not talk something about how to make an eye catching shots (because I'm still struggling myself on that too lol), but I will bring a more technical topic to ensure that you use the most out of your camera features to produce a kind of pro quality captures.
This graph seems meaningless for me when I first time started my hobby in photography. Gratefully, now I realize how this feature can help me a lot to produce a kind of balance image and despite of this 'so technical' appearance, it is pretty much simple to understand this feature.
Basically, histogram explains visually on how your exposure spreads in your shot. Left area explains darkness while right area describes the brightness. Look at below figure for easier reference.
Underexposed shots tend to produce dark image and it will damage the details if you do not pay attention on it. Same with overexposed case. The image will be seen too bright and the details are failed to be preserved on that overexposed area. I can say that how expert you are in post processing method, you still can't completely retrieve the details that are lost in over/under exposed area. Below are the samples of under / overexposed shot complete with how the histogram looks like. To be noted that below shots haven't undergone any editing process - so it will be the original file as it captured on the RAW.
Underexposed shot sample - you may see on the histogram located on the right side that the dominant pixels are peaked up on shadow part, resulting a darker look on the foreground. Notice that this shot also got a bit over-exposed on highlight area.
Overexposed shot sample - It can be seen that the histogram spreads are dominant on the highlight area, resulting brighter / white looks on the sky.