Image histogram

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An image histogram is type of histogram which acts as a graphical representation of the tonal distribution in a digital image.^[1] It plots the number of pixels for each tonal value. By looking at the histogram for a specific image a viewer will be able to judge the entire tonal distribution at a glance.

Image histograms are present on many modern digital cameras. Photographers can use them as an aid to show the distribution of tones captured, and whether image detail has been lost to blown-out highlights or blacked-out shadows.^[2]

The horizontal axis of the graph represents the tonal variations, while the vertical axis represents the number of pixels in that particular tone.^[1] The left side of the horizontal axis represents the black and dark areas, the middle represents medium grey and the right hand side represents light and pure white areas. The vertical axis, on the other hand, represents the size of the area which is captured in each one of these zones.

[edit] Image manipulation and histograms

Image editors typically have provisions to create a histogram of the image being edited. The histogram plots the number of pixels in the image (vertical axis) with a particular brightness value (horizontal axis). Algorithms in the digital editor allow the user to visually adjust the brightness value of each pixel and to dynamically display the results as adjustments are made.^[3] Improvements in picture brightness and contrast can thus be obtained.

[edit] See also

• Histogram
• Image editing
• Color histogram, a multidimensional histogram of the distribution of color in an image
• Histogram equalization

[edit] References

1. ^ ^{a b} Ed Sutton. "Histograms and the Zone System". Illustrated Photography. http://www.illustratedphotography.com/photography-tips/basic/contrast. 
2. ^ Michael Freeman (2005). The Digital SLR Handbook. Ilex. ISBN 1904705-36-7. 
3. ^ Martin Evening (2007). Adobe Photoshop CS3 for Photographers: A Professional Image Editor's Guide.... Focal Press. ISBN 0240520289. http://books.google.com/books?id=0XZO93ZcbqkC&pg=PA136&dq=%22image+histogram%22&lr=&as_brr=0&ei=dvL2R--yFI2AsgPP7Z2FCg&sig=UoCi37U--m3IUzm6fUG-YB3za_Y#PPA136,M1.