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Recipe 11.7. Converting Among Image Formats
Credit: Doug Blanding
Problem
Your image files are in various formats (GIF, JPG, PNG, TIF, BMP),
and you need to convert among these formats.
Solution
The Python Imaging Library (PIL)
can read and write all of these formats; indeed, net of
user-interface concerns, image-file format conversion using PIL boils
down to a one-liner:
Image.open(infile).save(outfile)where filenames infile and
outfile have the appropriate file
extensions to indicate what kind of images we're
reading and writing. We just need to wrap a small GUI around this
one-liner functionalityfor example:
#!/usr/bin/env pythonNeeding 80 lines of GUI code to wrap a single line of real
import os, os.path, sys
from Tkinter import *
from tkFileDialog import *
import Image
openfile = '' # full pathname: dir(abs) + root + ext
indir = ''
outdir = ''
def getinfilename( ):
global openfile, indir
ftypes=(('Gif Images', '*.gif'),
('Jpeg Images', '*.jpg'),
('Png Images', '*.png'),
('Tiff Images', '*.tif'),
('Bitmap Images', '*.bmp'),
("All files", "*"))
if indir:
openfile = askopenfilename(initialdir=indir, filetypes=ftypes)
else:
openfile = askopenfilename(filetypes=ftypes)
if openfile:
indir = os.path.dirname(openfile)
def getoutdirname( ):
global indir, outdir
if openfile:
indir = os.path.dirname(openfile)
outfile = asksaveasfilename(initialdir=indir, initialfile='foo')
else:
outfile = asksaveasfilename(initialfile='foo')
outdir = os.path.dirname(outfile)
def save(infile, outfile):
if infile != outfile:
try:
Image.open(infile).save(outfile)
except IOError:
print "Cannot convert", infile
def convert( ):
newext = frmt.get( )
path, file = os.path.split(openfile)
base, ext = os.path.splitext(file)
if var.get( ):
ls = os.listdir(indir)
filelist = [ ]
for f in ls:
if os.path.splitext(f)[1] == ext:
filelist.append(f)
else:
filelist = [file]
for f in filelist:
infile = os.path.join(indir, f)
ofile = os.path.join(outdir, f)
outfile = os.path.splitext(ofile)[0] + newext
save(infile, outfile)
win = Toplevel(root)
Button(win, text='Done', command=win.destroy).pack( )
# Divide GUI into 3 frames: top, mid, bot
root = Tk( )
root.title('Image Converter')
topframe = Frame(root, borderwidth=2, relief=GROOVE)
topframe.pack(padx=2, pady=2)
Button(topframe, text='Select image to convert',
command=getinfilename).pack(side=TOP, pady=4)
multitext = "Convert all image files\n(of this format) in this folder?"
var = IntVar( )
chk = Checkbutton(topframe, text=multitext, variable=var).pack(pady=2)
Button(topframe, text='Select save location',
command=getoutdirname).pack(side=BOTTOM, pady=4)
midframe = Frame(root, borderwidth=2, relief=GROOVE)
midframe.pack(padx=2, pady=2)
Label(midframe, text="New Format:").pack(side=LEFT)
frmt = StringVar( )
formats = ['.bmp', '.gif', '.jpg', '.png', '.tif']
for item in formats:
Radiobutton(midframe, text=item,
variable=frmt, value=item).pack(anchor=NW)
botframe = Frame(root)
botframe.pack( )
Button(botframe, text='Convert', command=convert).pack(
side=LEFT, padx=5, pady=5)
Button(botframe, text='Quit', command=root.quit).pack(
side=RIGHT, padx=5, pady=5)
root.mainloop( )
functionality may be a bit extreme, but
it's not all that far out of line in my experience
with GUI coding ;-).
Discussion
I needed this tool when I was making .avi files
from the CAD application program I generally use. That CAD program
emits images in .bmp format, but the
AVI[1]-generating program I normally use requires images in
.jpg format. Now, thanks to the little script in
this recipe (and to the power of Python, Tkinter, and most especially
PIL), with a couple of clicks, I get a folder full of images in
.jpg format ready to be assembled into an AVI
file, or, just as easily, files in .gif ready to
be assembled into an animated GIF image file.
[1] AVI (Advanced Visual Interface)
I used to perform this kind of task with simple shell scripts on
Unix, using ImageMagick's convert
command. But, with this script, I can do exactly the same job just as
easily on all sorts of machines, be they Unix, Windows, or Macintosh.I had to work around one annoying problem to make this script work as
I wanted it to. When I'm selecting the location into
which a new file is to be written, I need that dialog to give me the
option to create a new directory for that purpose. However, on
Windows NT, the Browse for Folder dialog doesn't
allow me to create a new folder, only to choose among existing ones!
My workaround, as you'll see by studying this
recipe's Solution, was to use instead the Save As
dialog. That dialog does allow me to create a new folder. I do have
to indicate the dummy file in that folder, and the file gets ignored;
only the directory part is kept. This workaround is not maximally
elegant, but it took just a few minutes and almost no work on my
part, and I can live with the result.
See Also
Information about Tkinter can be obtained from a variety of sources,
such as Fredrik Lundh, An Introduction to
Tkinter, (PythonWare: http://www.pythonware.com/library), New
Mexico Tech's Tkinter
Reference (http://www.nmt.edu/tcc/help/lang/python/docsl),
Python in a Nutshell, and various other books;
PIL is at http://www.pythonware.com/products/pil/.
