如何在Python中将直方图数据保存到CSV文件中？

Question

From the below python code I can plot the histogram of three color components of a color image . But I would like to save this histogram data to a CSV file to get this histogram in future. How can I do this?

from PIL import Image
import matplotlib.pyplot as plt

def getRed(redVal):
    return '#%02x%02x%02x' % (redVal, 0, 0)

def getGreen(greenVal):
    return '#%02x%02x%02x' % (0, greenVal, 0)

def getBlue(blueVal):
    return '#%02x%02x%02x' % (0, 0, blueVal)

# Create an Image with specific RGB value
image = Image.open("baboon.ppm")
# Modify the color of two pixels
image.putpixel((0,1), (1,1,5))
image.putpixel((0,2), (2,1,5))

# Display the image
#image.show()
# Get the color histogram of the image
histogram = image.histogram()
# Take only the Red counts
l1 = histogram[0:256]
# Take only the Blue counts
l2 = histogram[256:512]
# Take only the Green counts
l3 = histogram[512:768]
plt.figure(0)
# R histogram
for i in range(0, 256):
    plt.bar(i, l1[i], color = getRed(i), edgecolor=getRed(i), alpha=0.3)

# G histogram
plt.figure(1)
for i in range(0, 256):
    plt.bar(i, l2[i], color = getGreen(i), edgecolor=getGreen(i),alpha=0.3)


# B histogram
plt.figure(2)
for i in range(0, 256):
    plt.bar(i, l3[i], color = getBlue(i), edgecolor=getBlue(i),alpha=0.3)

plt.show()

Here is the output for red channel histogram

Answer 1

l1, l2 and l3 are just lists.
You can convert them to one string and write the string to a plain text file eg:

def writeCsv( RList, GList, BList ):
    outString = '\r\n'.join([
        ';'.join( map( str, RList ) ),
        ';'.join( map( str, GList ) ),
        ';'.join( map( str, BList ) )
    ])
    print( outString )
    f = open( 'csv_file.csv', 'wb' )
    f.write( outString )
    f.close()

def loadCsv():
    f = open( 'csv_file.csv', 'rb' )
    out = f.read()
    f.close()
    out = out.split('\r\n');
    out = [ x.split(';') for x in out ]
    return out

writeCsv( l1, l2, l3 )
print('--')
print( loadCsv() )

It might be desirable to save the file like 'RGB,RGB,...' instead of 'RRR...,GGG...,BBB...':

def writeCsvRGB( RList, GList, BList ):
    temp = zip( RList, GList, BList )
    temp = [ ';'.join( map( str, x ) ) for x in temp ]
    temp  = '\r\n'.join( temp )
    print( temp )

    f = open( 'csv_file.csv', 'wb' )
    f.write( temp )
    f.close()