Camera’s LCD displays are pretty bad at accurately representing what the photo looks like, which is why you should be using Histograms. Histograms give you a mathematical representation of how well exposed a photo is, which helps you to get the best photo possible when out on a shoot.
What is it and what does it tell you?
The histogram shows you a scientific review of an exposure after you’ve taken it. It essentially tells you how evenly exposed a photo is. LCD screens aren’t very good at telling you this information because their effects are largely based on the ambient lighting conditions you’re in and the brightness of the screen itself. You’ll find an option to view the histogram in all cameras, and some compacts that don’t rely on the viewfinder to compose a photo will also show you the histogram in realtime.
How do I read the histogram?
A histogram is mapped out by brightness on a grayscale. Black is on the left, white is on the right and all they different shades of gray are in between.
In a standard jpg image there are 256 different recorded values of brightness; 0 is pure black and 255 is pure white. These 256 values are mapped out in a histogram and each pixel from the image is assigned to a value. Now, let’s have a look at what that looks like:
The image above has been correctly exposed and the majority of pixels are away from the black and white values in the histogram and what may appear to be black in the photo is actually just a very dark shade of grey.
If you were taking a photo at night, your results may be very different, but you always want to stay away from the pure black or pure white values. Having pixels in these values means that your photo has either been overexposed or underexposed and needs to be retaken as there is detail missing. These details can’t be recovered in photoshop because it’s no longer a shade of a color, it’s pure black/white.
Have a look below at an overexposed image and an overexposed image with their respective histograms.
It’s also possible to see your histograms in 3 channels of color – red, green and blue (also known as RGB). For the correctly exposed image i used first, it looks like this:
Using this version of the histogram is most important when shooting brightly colored objects as it’s possible to blow out (overexpose to the extent that information is lost) the corresponding channel of color without it appearing in the main histogram.
Now that you understand how histograms work, you’ll start to find yourself using it more and more when taking photos. They’re a great way of making sure that you’re getting it right in the camera, and stop you from relying on a computer to finish off your photos.
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