downsampling images as a function in Python

Question

I am trying to resample some tiff files from 2000*2000 to 500*500. I have created a function and I tried for one file and it worked nicely. Now I want to apply it for all the available file I have.

I want to write the output of the function and I have written the code based on my knowledge and I receive error on the writing out_file. I have copied the both function and main code for your consideration. The main code just read the tif files according to their naming and applies the function. I would be thankful if sb could guide me where my mistake is.

#*********function********************
 def ResampleImage(infile):

       fp = open(infile, "rb")
       p = ImageFile.Parser()

       while 1:
           s = fp.read()
           if not s:
               break
           p.feed(s)

      img = p.close()


      basewidth = 500
      wpercent = (basewidth / float(img.size[0]))
      hsize = int((float(img.size[1]) * float(wpercent)))
      outfile=img.resize((basewidth, hsize), PIL.Image.ANTIALIAS)

      return outfile

 #********* main code********

 import os,sys
 import ImageResizeF
 import PIL
 from PIL import Image
 from PIL import Image,ImageFile

 tpath = 'e:/.../resampling_test/all_tiles/'


 tifext = '.tif'
 east_start = 32511616
 north_start = 5400756
 ilist = range (0,14)
 jlist = range (0,11)

 north = north_start
 ee = ',4_'
 en = ',2'


 for i in ilist:              
    east = east_start
    north = north_start + i * 400
    snorth = str (north)

    for j in jlist:
       east = east_start + j * 400
       seast = str (east)      
       infile = tpath + seast + ee + snorth + en + tifext
       output = tpath + seast + ee + snorth + en + '_res'+tifext
       out_file = ImageResizeF.ResampleImage(infile)
       out_file.write (output)
       out_file.close ()   

Answer 1

Your error is probably related to what you are returning from ImageResizeF.ResampleImage, is it a file handle? Otherwise you are doing it wrong because you cannot close() something which is not a file handle. You should do the whole file processing inside the function or return an image object, for example:

def process_image(image):
    "Processes the image"
    image.resize((x, y), Image.ANTIALIAS) # or whatever you are doing to the image
    return image

image = Image.open('infile.tiff')
proc_image = process_image(image)
proc_image.save('outfile.tiff')