| Photoshop Tutorials » Nature » Histograms |
Photoshop produces red, green and blue histograms inside an RGB image, when it's done it puts the results into a composite version and displays it as the standard view. How that composite view is calculated decides how we see clipping inside our images - and as you'll bear witness, things aren't always what they seem!
One of the most useful tools available to digital SLR photographers is the histogram, but it is also one of the least understood. Here we explain what function it provides and how you can use it to check exposure on location. In basic terms, a histogram is a two-dimensional graph, often resembling a range of mountain peaks, that represents an image's tonal extent. Whilst, at first glance, histograms might appear quite complex and confusing, they are actually very simple to read. They are an essential aid for digital SLR photographers striving to achieve consistently correct exposures in-camera and are a more accurate method of assessing exposure than looking at images you've taken on the LCD monitor. Therefore, if you are not already in the habit of regularly reviewing your image' histogram, it is time you did so. With the help of this guide, you will soon feel confident assessing histograms, as we cover all the key areas of histograms in an easy to understand, jargon-free language. What is a histogram? A histogram is a visual representation of an image's tonal range. The horizontal axis indicates the picture's extent from pure black to pure white. Pure black is represented by 0 (far left), while pure white is indicated by 255 (far right). The vertical axis illustrates exactly how many pixels have that particular value. Therefore, by simply looking at an image's histogram, a photographer can tell whether the picture is made up of predominantly light, dark or mid-tones. Histograms come in all shapes and sizes. Although their appearance is greatly dictated by the colour and tone of the subject itself, for general scenes, a histogram with a large number of pixels (or a sharp peak) grouped at either edge is an indication of poor exposure. For example, a histogram with a large number of black pixels (grouped to the left) often signifies underexposure. Consequently, subject details will be obscured in the shadow areas. A large number of pixels grouped to the right of the histogram normally indicates an image which is overexposed. The image's highlights will burn out (or 'clip') and this detail is irretrievable. A graph with a narrow peak in the middle and no (or few) black or white pixels indicates an image lacking contrast and so the results may look flat and lifeless. So what should a histogram look like? This is a tricky one to answer. Despite what some people may say, there is no such thing as the 'perfect histogram'. It simple tells us how a picture is expo...
One of the most important and valuable tools that Photoshop gives us when editing, retouching or restoring images is the histogram. In fact, histograms are so valuable, they're not limited to just Photoshop. You'll find histograms in lots of other image editing programs as well, like Photoshop Elements, Adobe Lightroom, the Camera Raw plug-in, and more! Many digital cameras today also come with a handy histogram feature that lets you view the exposure of your photos right after you snap them! For something so simple, it's hard to imagine life without histograms, at least for anyone who's serious about the quality of their photos.
