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The histogram is a vector containing the number of pixels with the same color (temperature)
ie. h(34)=22 means that there are 22 pixels with the color gray#34.

histogram function:


M horizontal image size (pixels)
N vertical image size (pixels)
d Dirac function (d(k)=1 for k=0, d(k)=0 else)
i takes values in {0,1,.. , L-1} interval
L the number of gray levels


'reservoir' image

the histogram associated with the picture on the left tels this story:
- the picture has many 'dark' pixels
- most pixels have gray levels from 0 to 112 (11.4 degrees Celsius - 53.4 degrees)
- we have a maximum at gray level 0 (black) (11.4 degrees)

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