One of the most useful things a digital camera has been blessed with is the so-called histogram which is a diagram showing how an image may have been exposed. This histogram has often proved to be completely invaluable when it comes to assessing how well the exposure was, especially as most cameras display has a very limited scale and it is difficult to assess the exposure just by looking at the picture.
Zero Control: A histogram is a graph showing the tones (from blackest black to whitest white) available in a digital image. The height of the graph is a measure of the number of image pixels that have a particular shade. A histogram can now be seen in most cameras and image software.
The camera histogram can be very helpful to evaluate the exposure. High bars in the left says that the image is too dark (underexposed), while the high bars in the right wing says that the image is too light (overexposed). It is often said that the photo has been clipped in the shadows and highlights. When the correct exposure is achieved, the whole graph fit in the histogram.
In an image processing program that the histogram can be a good aid to see how the tones are affected in various finishing operations, such as when the image is adjusted using the tool "Levels".
Partial Control: The number of possible tones in the image is measured on a scale between 0 and 255. From black (0) to white (255), with 254 shades of gray in between. The histogram consists of 256 really narrow bars next to each other.
A histogram with tones only in the center reveals that the image has low contrast. In general, we want the histogram will be stretched across the whole spectrum.
Sometimes the difference between dark and light tones are so great that the camera fails to capture the scene in one exposure. In these cases, the histogram is stretched out and become cut off in both left and right edge.
The histogram should be studied together with the current image. If we shoot a sunset with the silhouette of the foreground, we do not want details in the shadow parties. A truncated histogram is not always unwelcome.
Full Control: Since the histogram takes into account the current camera settings, it is not always an accurate reflection of exposure if you shoot in RAW format. Quite often an image with a truncated histogram can be salvaged in the RAW conversion.
The ordinary histogram is based on the total intensity of the image. A histogram can look ok, although the details have been lost in some areas of color. To be really sure we need to examine the histogram of each color channel.
Morris Scjomin has been a professional photographer for over 10 years, practicing exclusively in the field of portraiture, still life, and documentary images. He has an affection and a passion for Camera Lenses. If you work with an image, you want the best possible starting point. If you first learned to read the histogram, it could save you many problems, both when you're shooting and when editing.
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