Radiografic inspections. An image has grey levels in the range 54 to 180. The co

Question

Radiografic inspections.

An image has grey levels in the range 54 to 180. The contrast is enhanced using contrast spreading, where the new grey levels are in the range 0 to 255. What would the new values be for pixels which had original values of 120?

The histogram below shows the number of pixels of each value in a 40 x 40 image which uses 3-bits per pixel. For example, there are 50 pixels with a value of zero. What is the mean value of the image rounded to the nearest whole value?

Explanation / Answer

(a) The new value for 120 is calculated as follows:

new value = (120-54)*((255-0)/(180-54)) = 133.57 = 134

(b) Mean value of the image = ((50*0)+(150*1)+(250*2)+(400*3)+(300*4)+(250*5)+(100*6)+(100*7))/1600

= 5600/1600 = 3.5

So, the mean value of the image around the nearest whole value = 4.

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