One of the best ways to improve your images when you are new to photography is to understand how to read a histogram.
The preview screen on the back of your DSLR camera doesn’t give you an accurate representation of what your photograph looks like.
If you’re shooting tethered to Lightroom and are able to see a larger rendition of your image on your monitor, you still may not know if it’s properly exposed.
LCD screens and computer monitors aren’t very good at conveying exposure. This is because the brightness of the screen and ambient lighting conditions affects them.
Also, the camera’s LCD screen is small. It’s easy to miss smaller blown out highlights or areas where you could be missing shadow detail.
By understanding how to read a histogram, you can know exactly how evenly exposed a photo is.
What Is a Histogram and How to Read It
A histogram is a mathematical representation of the tonal range of an image. Tonal range refers to the number of tones between the darkest part of your image to the lightest.
The histogram maps out brightness on a grayscale. Black is on the left, while white is on the right. You can find all of the shades of grey in between.
Each image file has a scale of values of brightness. For a standard .jpg image, there are 256 different recorded values of brightness: 0 is pure black and 255 is pure white.
A histogram maps out the given brightness values; each pixel from the image is assigned to a value. The height of each column on the vertical (Y) axis is determined by how many pixels are assigned to that column.
A colour photography histogram has three colours: red, green, and blue. It will appear grey in areas where they overlap.
The image of the apple pie below has been correctly exposed and the majority of its pixels are away from the black and white values in the histogram.
What may appear to be black in the photo is actually just a very dark shade of grey.
The reason that the majority of the pixels appear on the-left hand side of the histogram is because it’s a dark and moody style image.
However, you can tell it’s not underexposed because there is still a bit of a gap between the assigned brightness values and the very end of the histogram. The columns don’t touch the end.
If you have pixels touching the very end of your histogram, it means the image is either underexposed, or overexposed. You’re missing details you can’t recover in Photoshop later. At this point, you should adjust your exposure and re-shoot.
Have a look below at these two food images with their respective histograms. One is overexposed, while the other is underexposed.
To know if an image has lost detail, you can also turn on the clipping warning in Lightroom. These are little triangles in the upper corner of the histogram.
When these appear and change colour, Lightroom is warning you regarding detail loss in the image. When the triangle is white, you have lost detail. This will also appear in the image itself.
Red will show you the blown out areas, while blue will show you the areas that are missing shadow detail.
One thing to note, however, is that you want to be making creative decisions along with the information from your histogram or the clipping warnings in Lightroom. Sometimes clipped shadows don’t matter in a particular image.
The same can go for blown out highlights–especially in a backlit image. It’s up to you to use your discretion as to when it is negatively affecting your exposure.
In the picture of the cobbler on the left below, you can see the whole back of the image was blown out. This is because the image was backlit with window light. The important areas of lightness, such as the white plate, are properly exposed.
The dark image of the croissant has some areas where it has lost shadow detail, particularly around the edges of the props. Check out their respective histograms.
Many cameras have a single histogram. To really get an accurate reading of your exposure, you need to look at your histograms in the three channels of colour: red, green and blue–also known as RGB.
The regular histogram lumps all of these colours together. This means you don’t always know if you are overexposing or underexposing a specific colour.
The RGB histogram is similar to the regular one, but with a separate histogram for each colour channel.
The goal is the same though. You don’t want to underexpose or overexpose any of the colour channels. Look at each channel’s histogram to ensure the graph isn’t bunching up to one side.
It’s important to note that each colour channel’s histogram may be drastically different from image to image. What you will see really depends on the colours in the photo and how bright they are.
Using this version of the histogram is most important when shooting brightly coloured subjects, otherwise it’s possible to blow out the corresponding channel of colour without it appearing in the main histogram.
You can end up overexposing the image and losing information.
When taking pictures, turn on the histogram view function on your camera and monitor your histograms alongside your LCD screen or your monitor when tethered to Lightroom.
The goal is to always try your best to get your exposures right in camera.
It will cut down the amount of time you spend in post-processing And you’ll rely less on programs like Photoshop and Lightroom to fix things that you can get right in-camera.
Photography is a blend of artistry and science. Learning as much as you can about the technical side can help you make better creative decisions.
Once you have become fluent in the language of the histogram, you’ll stop struggling with exposure and will find you have a lot more consistency in your photography.
Do you want to know more about photography terms? Check out our new post about photography slang next!
A note from Josh, ExpertPhotography's Photographer-In-Chief:
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