scripts/png.py

   1 import struct, zlib, sys
   2
   3 class image:
   4         w = 0
   5         h = 0
   6         data = []
   7
   8 def read_tga(f):
   9         image = f.read()
  10         img_type = struct.unpack("<B", image[2:3])[0]
  11         img_bpp = struct.unpack("<B", image[16:17])[0]
  12         img_width = struct.unpack("<H", image[12:14])[0]
  13         img_height = struct.unpack("<H", image[14:16])[0]
  14
  15         if img_type != 2 or img_bpp != 32:
  16                 print "image must be a RGBA"
  17
  18         start = 18+struct.unpack("B", image[0])[0]
  19         end = start + img_width*img_height*4
  20         image_data = image[start:end] # fetch raw data
  21         return image_data
  22
  23 def write_tga(f, w, h, bpp, data):
  24         f.write(struct.pack("<BBBHHBHHHHBB", 0, 0, 2, 0, 0, 0, 0, 0, w, h, bpp, 0) + data)
  25
  26
  27
  28
  29
  30 def load_png(f):
  31         def read(fmt): return struct.unpack("!"+fmt, f.read(struct.calcsize("!"+fmt)))
  32         def skip(count): f.read(count)
  33
  34         # read signature
  35         if read("cccccccc") != ('\x89', 'P', 'N', 'G', '\r', '\n', '\x1a', '\n'):
  36                 return 0
  37
  38         # read chunks
  39         width = -1
  40         height = -1
  41         imagedata = ""
  42         while 1:
  43                 size, id = read("I4s")
  44                 if id == "IHDR": # read header
  45                         width, height, bpp, colortype, compression, filter, interlace = read("IIBBBBB")
  46                         if bpp != 8 or compression != 0 or filter != 0 or interlace != 0 or (colortype != 2 and colortype != 6):
  47                                 print "can't handle png of this type"
  48                                 print width, height, bpp, colortype, compression, filter, interlace
  49                                 return 0
  50                         skip(4)
  51                 elif id == "IDAT":
  52                         imagedata += f.read(size)
  53                         skip(4) # read data
  54                 elif id == "IEND":
  55                         break # we are done! \o/
  56                 else:
  57                         skip(size+4) # skip unknown chunks
  58
  59         # decompress image data
  60         rawdata = map(ord, zlib.decompress(imagedata))
  61
  62         # apply per scanline filters
  63         pitch = width*4+1
  64         bpp = 4
  65         imgdata = []
  66         prevline = [0 for x in xrange(0, (width+1)*bpp)]
  67         for y in xrange(0,height):
  68                 filter = rawdata[pitch*y]
  69                 pixeldata = rawdata[pitch*y+1:pitch*y+pitch]
  70                 thisline = [0 for x in xrange(0,bpp)]
  71                 def paeth(a, b, c):
  72                         p = a + b - c
  73                         pa = abs(p - a)
  74                         pb = abs(p - b)
  75                         pc = abs(p - c)
  76                         if pa <= pb and pa <= pc:
  77                                 return a
  78                         if pb <= pc:
  79                                 return b
  80                         return c
  81
  82                 if filter == 0: f = lambda a,b,c: 0
  83                 elif filter == 1: f = lambda a,b,c: a
  84                 elif filter == 2: f = lambda a,b,c: b
  85                 elif filter == 3: f = lambda a,b,c: (a+b)/2
  86                 elif filter == 4: f = paeth
  87
  88                 for x in xrange(0, width*bpp):
  89                         thisline += [(pixeldata[x] + f(thisline[x], prevline[x+bpp], prevline[x])) % 256]
  90
  91                 prevline = thisline
  92                 imgdata += thisline[4:]
  93
  94         raw = ""
  95         for x in imgdata:
  96                 raw += struct.pack("B", x)
  97
  98         #print len(raw), width*height*4
  99         write_tga(file("test2.tga", "w"), width, height, 32, raw)
 100         return 0
 101
 102 load_png(file("butterfly2.png", "rb"))