One of the revolutionary steps in the history of digital photography is being able to calculate and display an image’s histogram.
A graphic bar is showing the tonal distribution in an image, the histogram sorts and reveals the different luminosities of pixels distributed on a scale of brightness, from 0 to 255, or from black (left) to white (right), with 254 different shades of gray in between. The height of each bar corresponds to the number of pixels of the same shade.
Why should you care about the technical details? Because understanding the way, a histogram works allows you to review all your shots, check out exposure and whether some details have been lost in shadows or burnt in too much light.
If you open your Adobe Photoshop and select Window->Histogram or Image -> Histogram (depending on the soft version you use), you’ll see your image’s histogram and be able to clear out any luminosity and color problems.
When do we have a problem?
Although the answer to this question might seem obvious, no actual recipe guarantees a perfect image if you have a perfect histogram. The rule of thumb says that a correctly exposed image is observed in a histogram with smooth, gradually ascending and descending curves towards its extreme limits (0 and 255), as is the example on the left. Does this automatically exclude all the other possible histograms for being bad ones? Technically, yes, but don’t delete half of your images just yet.
Technical precision isn’t always satisfactory, nor is it mandatory, but understanding it will help you overcome common issues and will prove useful knowledge when you want to break the rules and capture different, unique perspectives through your photos.
With many pixels quite close to 0 value indicating plenty of dark areas, some of the details in the shadows are lost forever. There are also few to none pixels in the highlight area (255), turning the histogram above into a definitive proof of an underexposed image.
Combined histogram – How it helps us?
And there’s always the combed histogram, a unique example that only appears when image post-processing has been done in either Photoshop or some other similar soft. Why does this happen? Because playing with Levels or Curves (two settings available in all post-processing programs) involves contrast adjustments that cause a redistribution of tones with tone losses in the process, determining a comb-like histogram, hence the name.
The great thing is that most of the modern DSLRs have a histogram option available in their settings, allowing you to snap judge the quality of a shot on the spot and take another one if necessary.
Although an accurate exposure – underlined by a smooth histogram – confirms that your camera captured all details from both highlights and shadows, remember that people don’t care about pixels and tab graphs. They are impressed by the originality and authenticity they find in your images.
So learning the language of histograms will probably be enough to master perfect exposures, but learning when to say “No” to perfect exposures will get you one step closer to mastering photography.
Histogram – A tool every photographer should master?
You can’t consider yourself as a pro photographer if you don’t master all aspects of photography. You will have to use various settings to get excellent pictures in a wide array of situations and mastery of all tools at your disposal is a must if you want to succeed in this line of business.
The histogram is just another tool you should learn how to use. It isn’t anything new but it improved over the course of time and you should have improved with it. If you don’t know how to use it then you won’t sell many pictures you make as they won’t be as good as they could be with the use of the histogram.