April 11, 2017 at 8:38 am #1857
One of the greatest features of modern day cameras is that they can show you immediately what you have clicked. This helps you take another shot if something is not right. One of the reasons for trying another shot is because the picture does not look like what you visualized due to exposure errors created by camera metering. Most expert photographers can immediately find from the preview whether the picture is over or under exposed. One of the features that the cameras offer you is to show you a technical view of the exposure in the form of a “Histogram”. A digital picture is made of millions of pixels or dots, each having a brightness value ranging from black to white or darkest to brightest. A histogram simply groups the pixels by their brightness value and shows how many pixels are there in your picture that corresponds to each brightness value. Think of it as a bar chart with each bar representing a brightness value and the size of the bar representing the number of pixels of that brightness value that you have in your picture. The leftmost bar represents the darkest dot the camera can capture and the rightmost bar represents the brightest dot the camera can capture.
If you look at the histogram closely, it shows a few vertical lines as well. These are called “Exposure Zones”. The left most exposure zone is the Black Zone, a brightness value that humans perceive as black. The next is a shadow zone followed by mid-tone zone, highlight zone and white zone. We can make many inferences about the exposure of a picture by looking at the histogram. These inferences can help us make proper corrections to exposure irrespective of how good your camera LCD is in showing a proper replay of your picture.
- If you find many pixels crowded around the leftmost area, that is, the leftmost area is showing a high mountain, then you can rest assured that you are likely to lose details due to under exposure. Should I then increase the exposure? The answer lies in what you want to shoot. If you are shooting a silhouette against a Sunset, it is perfect to lose details. If you are shooting your family picture they may not like a picture in which the faces are not visible.
- Similarly, if you see a large mountain on the rightmost, it means that you are likely to see blown out areas in your picture. Again, you are the one to decide whether this is what you want.
- A histogram that generally starts with a small bar on the left rises to a high mountain in the center and tapers off to the right is a normal scene of medium contrast without too much of shadows and highlights. This is typically the scene during the day and under overcast clouds.
- A histogram with a mountain on the left and right and a valley in the center is a high-contrast image. A large bright flower against a dark background is one example of a high-contrast picture. You may want to make sure that the bright areas are more towards the highlight zone than the white zone to get a proper exposure on your flower.
Photo processing tools like Lightroom or Photoshop also show histogram during processing. Keep an eye on the histogram while adjusting the exposure. Apart from the 5-Zone histogram bars they also have two triangular shaped markers on either end of the histogram. These markers are generally gray. While increasing the exposure if you find that the marker on the right side lights up, it means that you are going to create blown-out whites in your picture. A blown-out area is an eye sore and contains no details. Similarly, while reducing the exposure the triangle on the left may light up, indicating that there are going to be black areas without details. Try looking at the histogram, next time you are shooting pictures.April 11, 2017 at 5:39 pm #1861
The Histogram in Lightroom has the colours green, light & dark blue, yellow, red and a large grey area. What does it represent ?
Very well written article. Precise and in simple language, making it easy to understand, especially for learners!
Thank you !April 11, 2017 at 11:58 pm #1864
Lightroom actually shows three histograms in one window, each histogram representing the primary colors Red, Green, and Blue. The secondary colors Cyan, Magenta, and Yellow appear wherever the histogram areas of primary colors are overlaid on one another. The place where all the three primary colors are present is shown as Gray. You can individually figure out whether your adjustments, say saturation adjustment, is going to push any of the colors beyond the edge.
Thanks for reading.April 12, 2017 at 9:16 pm #1870
Thank you for the explanation! Murali. Excellent article!
Do you check the histogram often on your camera ?April 12, 2017 at 9:38 pm #1872
I check the histogram when the lighting conditions are difficult.April 13, 2017 at 4:14 pm #1888
Ok, Thank you.May 30, 2017 at 10:55 pm #2150
When and how to make adjustments to RGB in colour histogram?May 30, 2017 at 11:39 pm #2151
The only general rules are to keep an eye on the histogram while making changes so that the adjustment does not cause any color to move beyond the edges. Reduction in exposure could make some colors to fall off the left edge causing details to be lost into blackness. Similarly, Increasing the exposure may make the colors to exceed the right edge resulting in bright patches.May 30, 2017 at 11:49 pm #2152
Thank you Murali for the prompt reply!
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