[python] How to obtain image size using standard Python class (without using external library)?

That code does accomplish 2 things:

• Getting the image dimension

• Find the real EOF of a jpg file

Well when googling I was more interest in the later one. The task was to cut out a jpg file from a datastream. Since I I didn't find any way to use Pythons 'image' to a way to get the EOF of so jpg-File I made up this.

Interesting things /changes/notes in this sample:

• extending the normal Python file class with the method uInt16 making source code better readable and maintainable. Messing around with struct.unpack() quickly makes code to look ugly

• Replaced read over'uninteresting' areas/chunk with seek

• Incase you just like to get the dimensions you may remove the line:

  hasChunk = ord(byte) not in range( 0xD0, 0xDA) + [0x00] 
  

  ->since that only get's important when reading over the image data chunk and comment in

  #break
  

  to stop reading as soon as the dimension were found. ...but smile what I'm telling - you're the Coder ;)

    import struct
    import io,os
  
    class myFile(file):
  
        def byte( self ):
             return file.read( self,  1);
  
        def uInt16( self ):
             tmp = file.read( self,  2)
             return struct.unpack( ">H", tmp )[0];
  
    jpeg = myFile('grafx_ui.s00_\\08521678_Unknown.jpg', 'rb')
  
    try:
        height = -1
        width  = -1
        EOI    = -1
  
        type_check = jpeg.read(2)
        if type_check != b'\xff\xd8':
          print("Not a JPG")
  
        else:
  
          byte = jpeg.byte()
  
          while byte != b"":
  
            while byte != b'\xff': byte = jpeg.byte()
            while byte == b'\xff': byte = jpeg.byte()
  
  
            # FF D8       SOI Start of Image
            # FF D0..7  RST DRI Define Restart Interval inside CompressedData
            # FF 00           Masked FF inside CompressedData
            # FF D9       EOI End of Image
            # http://en.wikipedia.org/wiki/JPEG#Syntax_and_structure
            hasChunk = ord(byte) not in range( 0xD0, 0xDA) + [0x00]
            if hasChunk:
                 ChunkSize   =  jpeg.uInt16()  - 2
                 ChunkOffset =  jpeg.tell()
                 Next_ChunkOffset = ChunkOffset + ChunkSize
  
  
            # Find bytes \xFF \xC0..C3 That marks the Start of Frame
            if (byte >= b'\xC0' and byte <= b'\xC3'):
  
              # Found  SOF1..3 data chunk - Read it and quit
              jpeg.seek(1, os.SEEK_CUR)
              h = jpeg.uInt16()
              w = jpeg.uInt16()
  
  
              #break
  
  
            elif (byte == b'\xD9'):
                 # Found End of Image
                 EOI = jpeg.tell()
                 break
            else:
                # Seek to next data chunk
               print "Pos: %.4x %x" % (jpeg.tell(), ChunkSize)
  
            if hasChunk:       
               jpeg.seek(Next_ChunkOffset)
  
            byte = jpeg.byte()
  
          width  = int(w)
          height = int(h)
  
          print("Width: %s, Height: %s  JpgFileDataSize: %x" % (width, height, EOI))
    finally:
        jpeg.close()