CODEWITHSUNDEEP
pythonbinarypython-3.xhexjpeg
Tired Tove
Tired Tove

Reputation: 83

Python3 - parsing jpeg dimension info

I'm trying to write a python function to parse the width and height from a jpeg file. The code I currently have looks like this

import struct

image = open('images/image.jpg','rb')
image.seek(199)
#reverse hex to deal with endianness...
hex = image.read(2)[::-1]+image.read(2)[::-1]
print(struct.unpack('HH',hex))
image.close()

There are a couple of problems with this though, firstly I need to look through the file to work out where to read from (after ff c0 00 11 08), and secondly I need to avoid picking up data from embedded thumbnails. Any suggestions?

Upvotes: 5

Views: 4745

Answers (4)

Gringo Suave
Gringo Suave

Reputation: 31968

Further modernized, simplified, pep8d code from Acorn and manafire. There are further improvements that could be done, for example to be more efficient use a large block size, but good enough for a quick example:

import sys
from struct import unpack


with open(sys.argv[1], 'rb') as jpegfile:

    if jpegfile.read(2) == b'\xff\xd8':

        byte = jpegfile.read(1)
        h = w = -1
        while byte != b'':

            # skip early segments
            while byte != b'\xff':
                byte = jpegfile.read(1)
            while byte == b'\xff':
                byte = jpegfile.read(1)

            # read dimensions
            if byte >= b'\xC0' and byte <= b'\xC3':
                jpegfile.read(3)
                h, w = unpack('>HH', jpegfile.read(4))
                break
            else:
                size = int(unpack('>H', jpegfile.read(2))[0])
                jpegfile.read(size - 2)

            byte = jpegfile.read(1)

        print(f'Width: {w}, Height: {h}')
    else:
        print('Not a JPG!')

Upvotes: 0

manafire
manafire

Reputation: 6084

I couldn't get any of the solutions to work in Python3 because of the changes to bytes and strings. Building on Acorn's solution, I came up with this, which works for me in Python3:

import struct
import io

height = -1
width = -1

dafile = open('test.jpg', 'rb')
jpeg = io.BytesIO(dafile.read())
try:

    type_check = jpeg.read(2)
    if type_check != b'\xff\xd8':
      print("Not a JPG")
    else:
      byte = jpeg.read(1)

      while byte != b"":

        while byte != b'\xff': byte = jpeg.read(1)
        while byte == b'\xff': byte = jpeg.read(1)

        if (byte >= b'\xC0' and byte <= b'\xC3'):
          jpeg.read(3)
          h, w = struct.unpack('>HH', jpeg.read(4))
          break
        else:
          jpeg.read(int(struct.unpack(">H", jpeg.read(2))[0])-2)

        byte = jpeg.read(1)

      width = int(w)
      height = int(h)

      print("Width: %s, Height: %s" % (width, height))
finally:
    jpeg.close()

Upvotes: 4

tzot
tzot

Reputation: 96081

My suggestion: use PIL (the Python Imaging Library).

>>> import Image
>>> img= Image.open("test.jpg")
>>> print img.size
(256, 256)

Otherwise, use Hachoir which is a pure Python library; especially hachoir-metadata seems to have the functionality you want).

Upvotes: 1

Acorn
Acorn

Reputation: 50597

The JPEG section of this function might be useful: http://code.google.com/p/bfg-pages/source/browse/trunk/pages/getimageinfo.py

jpeg.read(2)
b = jpeg.read(1)
try:
    while (b and ord(b) != 0xDA):
        while (ord(b) != 0xFF): b = jpeg.read(1)
        while (ord(b) == 0xFF): b = jpeg.read(1)
        if (ord(b) >= 0xC0 and ord(b) <= 0xC3):
            jpeg.read(3)
            h, w = struct.unpack(">HH", jpeg.read(4))
            break
        else:
            jpeg.read(int(struct.unpack(">H", jpeg.read(2))[0])-2)
        b = jpeg.read(1)
    width = int(w)
    height = int(h)
except struct.error:
    pass
except ValueError:
    pass

Upvotes: 3

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