Bitmap/Histogram: Difference between revisions

=={{header|Nim}}==

<lang Nim>import bitmap

import grayscale_image

type Histogram = array[Luminance, Natural]

#---------------------------------------------------------------------------------------------------

func histogram*(img: GrayImage): Histogram =

## Build and return gray scale image histogram.

for lum in img.pixels:

inc result[lum]

#---------------------------------------------------------------------------------------------------

func median*(hist: Histogram): Luminance =

# Return the median luminance of a histogram.

var

inf = byte(0)

sup = Luminance.high

infCount, supCount = 0

while inf != sup:

if infCount < supCount:

inc infCount, hist[inf]

inc inf

else:

inc supCount, hist[sup]

dec sup

result = inf

#———————————————————————————————————————————————————————————————————————————————————————————————————

when isMainModule:

import ppm_read, ppm_write

# Read an image.

let image = readPPM("house.ppm")

# Build its histogram and find the median luminance.

let grayImage = image.toGrayImage

let hist = grayImage.histogram()

let m = hist.median()

echo "Median luminance: ", m

# Convert to black and white.

for pt in image.indices:

image[pt.x, pt.y] = if grayImage[pt.x, pt.y] < m: Black else: White

# Save image as a PPM file.

image.writePPM("house_bw.ppm")</lang>