- Image histogram
An image histogram is type of
histogram which acts as a graphical representation of the tonal distribution in adigital image cite web | work = Illustrated Photography | title = Histograms and the Zone System | author = Ed Sutton | url=http://www.illustratedphotography.com/photography-tips/basic/contrast] . It plots the number ofpixels 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 an can be used as an aid to show the photographer whether he or she has captured an adequate amount of tones or whether image detail has been lost to blown-out highlights or blacked-out shadows [cite book | title = The Digital SLR Handbook | author = Michael Freeman | publisher = Ilex | year = 2005 | isbn = 1904705-36-7] .The
horizontal axis of thegraph represents the tonal variations, while thevertical axis represents the number of pixels in that particular tone. 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.Image Manipulation and Histograms
Image editors have provisions to create an image 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. [cite book | title = Adobe Photoshop CS3 for Photographers: A Professional Image Editor's Guide... | author = Martin Evening | publisher = Focal Press | year = 2007 | isbn = 0240520289 | url = 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 ] Improvements in picture brightness and contrast can thus be obtained.Image histogram represents the number of pixel at the particular gray level h(rk)=nk where rk: is the number of pixel at the kthlevel nk: is the kthgray level normalized form of histogram is given by follow h(rk)=nk/n n(rk)/n=is the probability of gray level
ee also
*
Histogram
*Image editing
*Color histogram , a multidimensional histogram of the distribution of color in an image
*Histogram equalization References
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