The Histogram Basics
A digital SLR photographer’s most useful tool is the histogram. It is also something, which is very much misunderstood. The function the histogram supplies will be explained in this article as well as how you can use the histogram to check the exposure while on location.
A histogram is a two-dimensional graph that often resembles a wide range of mountain peaks that show the image’s tonal extent. At first glance, histograms appear very complex while being confusing. Unbelievably, if you understand histograms, they are quite simple to read and understand. Histograms are needed for digital SLR photography. Histograms enable photographers who are striving to achieve that constant correct exposure in-camera and this is a more accurate method of assessing the exposure as compared to looking at images you have already taken on your LCD monitor. If you are not in the habit of reviewing your images regularly with a histogram, it is time you began doing so. These tips will aid you in gaining the confidence needed in assessing histograms. We will now cover the key points of histograms in a language easy for you to understand.
What are histograms?
Histograms are visual representations of images tonal range. The horizontal axis shows the picture’s extent from black to pure light. Pure black is shown by “Q” which is far left, while pure white is indicated by “255” value. Simply viewing an image’s histogram, you can predict whether the picture is made up of largely light or dark mid-tones.
Histograms come in all sizes and shapes. Their appearance is determined by the color and tone of an object. A histogram with large number of pixels grouped at any edge is an indication of poor exposure. Image details will be obscured in the shadow areas. A large number of pixels grouped to the right of the histogram will indicate an image that is actually overexposed. The image’s highlights will clip and this detail is not good for any photographer. If you see a graph with a narrow peak in the middle with no black or white pixels, this will show the image lacking contrast therefore making the image look lifeless or flat.
What should a histogram really look like?
Despite what most say, there is no “perfect histogram”. All the histogram does is tell us about the exposure of the picture. This allows photographers to decide two important questions that are “when” and “how” to adjust the exposure settings. The histogram of a light scene will be different as compared to one with majority black tones or one with both tones that can be seen across the horizontal axis with the majority of the pixels near the middle, which is at 100 mid-points. It is best to avoid peaks to the right-hand side of the graphs; this will indicate the highlights are “burnt out” while resulting in lost detail.
You need to remember that with an even spread of pixels in your grayscale, it often considered desirable that you will also need to utilize your own discretion.
How can you check a pictures histogram?
Digital SLR’s will allow you to view the histogram on a LCD monitor during playback. To do this, simply press the playback button to view the image and then cycle through additional photo information screens until of course the histogram is displayed. You should make this your default setting therefore allowing you to quickly access the histogram as well as assessing exposure quickly after taking the picture. If the histogram shows underexposure, you must apply exposure compensation. If the pixels are grouped to the right and the image appears overexposed, simply dial in the negative compensation. Utilizing the histogram is a very reliable method of assessing exposure as compared to looking at images on a LCD screen especially when capturing outdoor images that can be in bright light. Something to remember is when interpreting histograms, it is always best to get a reasonable spread, which is coverage at least two thirds of the graph while avoiding sharp peaks toward either the left or right of the graph.
In theory, this is fine but in reality, it is never this simple. Creative photographers will shoot images or high-key images, which give the histograms with skewed pixels either toward the far left or far right. The images of a subject containing a large percentage of light or dark tones will have a histogram plainly to one edge of the graph. The histogram is not indicating an incorrect image instead; it is representing the style of the image.
About The Author:
Neil Austin enjoys writing about wedding photography especially digital wedding photography. To know more about him visit his website - Digital Wedding Guide.
