The Histogram is one of the most useful tools in Digital Photography yet it is one of the least understood and utilized. We've searched the web for ten of the best Histogram Tips and Tutorials to help us all to get the best possible exposure for our digital images. These tutorials focus upon both in camera histograms and histogram tools in imaging editing software. Add your tips, hints and suggested resources in comments below.
Histogram - Goldilocks and the Three Histograms - Photoxels gives an easy to understand definition and introduction to Histograms - 'The histogram is simply a graph that allows you to judge the brightness of an image. You can think of the area under the graph as comprising all the pixels in your captured digital image. The left side of the histogram depicts how many "dark" pixels you have captured; the right side, how many "bright" pixels you have captured.'
About Histograms takes the definition a little further - 'A histogram that shows more weight at the left of the graph represents a dark image, also called a low-key image. A histogram with more weight to the right of the graph represents a bright, or high-key, image. An image with a low-key histogram may be overexposed, and an image with a high-key histogram may be underexposed, though this is not necessarily always the case. Your eye--not a histogram--should always be your final judge. A histogram that shows a large flat area on either end of the graph, however, is most likely in need of some adjustment as you can see from the example below.'
A Short Course in Using Histograms illustrates this with this graphic (above). Their excellent tutorial gives a range of sample photos with histograms and gives hints on correcting images by using the Histogram tool in photoshop.
Understanding Histograms - so what does a good histogram look like? This tutorial argues - 'As mentioned earlier, with the possible exception of showing badly blown out highlights there really is no such thing as a bad histogram. They just are.' Some of the most stunning images (and this tutorial has some great examples) have histograms that might indicate real over or under exposure - so as with virtually any photographic 'rule', those associated with histograms are there to be broken.
Watch Your Histogram agrees with this - 'The overall shape of the histogram does not matter at all as it merely reflects the tonal distribution of the scene you photographed.' but also suggests that a good shape for a histogram - 'the ideal histogram should not indicate any over exposure or highlights are lost (and) not underexpose as you may lose shadow details but also most importantly get more noise. In conclusion the perfect digital exposure is as far to the right that there is no chance of overexposure. Unfortunately the real truth is not that easy.'
Color Concepts - Histograms is a useful little tool that uses an animated gif to illustrate a variety of sample images and their histograms.
Photoshop CS Histogram Tutorial is a tutorial exploring the dynamic Histogram tool in Photoshop CS - 'With Photoshop CS, the histogram has become dynamic. This means that, contrary to what happened in previous versions, the histogram will start moving in real-time as we drag sliders and curves in the Levels and Curves filter dialogue windows. Because it moves in tandem with the sliders and curves in those windows, we can immediately see when we are exaggerating or where there is still room for improvement.'
Underwater Digital Photography - Histograms - this tutorial focuses on the topic of underwater digital photography, in which they claim the Histogram is one of the best tools available.
A Practical Guide to Interpreting RGB Histograms has a nice conclusion (and a great overall tutorial) - 'It takes a little practice to be able to identify which parts of the histogram correlate to the different components and tonal range areas of the image. It is a skill well worth learning and not too different from the old black and white zone system. After a while you'll have an intuitive feel for where sky tones, clouds, dark or light earth tones, and bright highlights should fall in your image's histogram. You'll also know how much a 1/3 or 1/2 stop increase in exposure will shift the histogram to the right. Or, exactly how much a 1/3 or 1/2 stop decrease in exposure will shift the histogram to the left.'
PC Magazine have a good article on Histograms - they write:
'A search in pcmag.com for the word histo-gram reveals that dozens of cameras have this feature, and occasionally a review notes its disappointing absence. You may have seen these references or come across the histogram on your camera, and wondered what the heck a histogram is and why you should care.
Histograms are not widely understood, but taking a few moments to learn about them can improve your photography significantly. Histograms can show you clearly and immediately whether your images are overexposed, underexposed, or just right, and help you to make any necessary changes in order to compensate when reshooting the scene.'
So why do we need histograms? The information that they supply is information about under and over exposure. Whilst it doesn't determine the value of an image the histogram informs a photographer of exposure levels of their images which can be a very useful thing - especially when you're on location and trying to assess the value of a shot on your camera's tiny LCD.
