• PIL には、pixel ごとでなく、まとめてごそっと処理できる機能もあるが、とりあえずは使用しない

$ cd image
$ mkdir e2
$ cd e2

# e201.py ... make histogram
import Image
img = Image.open('sample.pgm')
width, height = img.size
hist = [0,]*256
for j in range(height):
    for i in range(width):
        pixval = img.getpixel((i, j))
        hist[pixval] += 1
for t in range(len(hist)):
    print '%3d %4d' % (t, hist[t])

$ python e201.py

# e201.py ... make histogram
import Image
import pylab
img = Image.open('sample.pgm')
width, height = img.size
hist = [0,]*256
for j in range(height):
    for i in range(width):
        pixval = img.getpixel((i, j))
        hist[pixval] += 1
pylab.plot(hist)
pylab.xlim((0, 255))
pylab.show()

#!/usr/bin/env python
# pgmhist.py ... make histogram
import sys
import Image
import pylab
if len(sys.argv) == 1:
    print 'Usage: %s pgmfile.pgm' % sys.argv[0]
    sys.exit(1)
else:
    fname = sys.argv[1]
img = Image.open(fname)
width, height = img.size
hist = [0,]*256
for j in range(height):
    for i in range(width):
        pixval = img.getpixel((i, j))
        hist[pixval] += 1
pylab.plot(hist)
pylab.xlim((0, 255))
pylab.show()

./pgmhist.py sample.pgm

# e202.py ... invert image
import Image
im0 = Image.open('sample.pgm')
width, height = im0.size
im1 = Image.new('L', (width, height))
for j in range(height):
    for i in range(width):
        x = im0.getpixel((i,j))
        y = 255 - x
        im1.putpixel((i,j), y)
im1.show()

• 1.pgm | 2.pgm | 3.pgm | 4.pgm | 5.pgm

• （、そのヒストグラムを e203.hist に作成しなさい。）は不要

y = 0            ... ( x < 64)
    (x - 64) * 2 ... (64 <= x < 196)
    255          ... ( x >= 196)

y = 2 * x               ... ( x < 128 )
    255 - 2 * (x - 128) ... ( x >= 128 )

# e205.py ... bright
import Image
 
# make lookup table
brighter = []
for x in range(256):
    y = 0.5 * (x - 255) + 255
    brighter.append(int(y))
 
im0 = Image.open('sample.pgm')
im1 = im0.point(brighter)
im1.show()