Getting list of pixel values from PIL

Question

Guys  I m looking for a bit of assistance  I m a newbie programmer and one of the problems I m having at the minute is trying to convert a black  amp  white  jpg image into a list which I can then modulate into an audio signal  This is part of a lager project to create a python SSTV program   I have imported the PIL module and am trying to call the built-in function  list im getdata     When I call it  python crashes  Is there some way of breaking down the image  always 320x240  into 240 lines to make the computations easier  Or am I just calling the wrong function   If anyone has any suggestions please fire away  If anyone has experience of generating modulated audio tones using python I would gladly accept any  pearls of wisdom  they are willing to impart  Thanks in advance

User · Answer

As I commented above  problem seems to be the conversion from PIL internal list format to a standard python list type  I ve found that Image tostring   is much faster  and depending on your needs it might be enough  In my case  I needed to calculate the CRC32 digest of image data  and it suited fine   If you need to perform more complex calculations  tom10 response involving numpy might be what you need

User · Answer

data   numpy asarray im    Notice In PIL  img is RGBA  In cv2  img is BGRA   My robust solution   def cv from pil img pil img       assert pil img mode   RGBA      return cv2 cvtColor np array pil img   cv2 COLOR RGBA2BGRA

User · Answer

pixVals   list pilImg getdata      output is a list of all RGB values from the picture     248  246  247    246  248  247    244  248  247    244  248  247    246  248  247    248  246  247    250  246  247    251  245  247    253  244  247    254  243  247

User · Answer

I assume you are getting an error like   TypeError   PixelAccess  object is not iterable      See the Image load documentation for how to access pixels    Basically  to get the list of pixels in an image  using PIL   from PIL import Image i   Image open  myfile png    pixels   i load     this is not a list  nor is it list   able width  height   i size  all pixels      for x in range width       for y in range height           cpixel   pixels x  y          all pixels append cpixel    That appends every pixel to the all pixels - if the file is an RGB image  even if it only contains a black-and-white image  these will be a tuple  for example    255  255  255    To convert the image to monochrome  you just average the three values - so  the last three lines of code would become    cpixel   pixels x  y  bw value   int round sum cpixel    float len cpixel       the above could probably be bw value   sum cpixel  len cpixel  all pixels append bw value    Or to get the luminance  weighted average    cpixel   pixels x  y  luma    0 3   cpixel 0      0 59   cpixel 1      0 11   cpixel 2   all pixels append luma    Or pure 1-bit looking black and white   cpixel   pixels x  y  if round sum cpixel     float len cpixel    gt  127      all pixels append 255  else      all pixels append 0    There is probably methods within PIL to do such RGB - gt  BW conversions quicker  but this works  and isn t particularly slow   If you only want to perform calculations on each row  you could skip adding all the pixels to an intermediate list   For example  to calculate the average value of each row   from PIL import Image i   Image open  myfile png    pixels   i load     this is not a list width  height   i size row averages      for y in range height       cur row ttl   0     for x in range width           cur pixel   pixels x  y          cur pixel mono   sum cur pixel    len cur pixel          cur row ttl    cur pixel mono      cur row avg   cur row ttl   width     row averages append cur row avg   print  Brighest row    print max row averages

User · Answer

Looks like PILlow may have changed tostring   to tobytes     When trying to extract RGBA pixels to get them into an OpenGL texture  the following worked for me  within the glTexImage2D call which I omit for brevity    from PIL import Image img   Image open  mandrill png   rotate 180  transpose Image FLIP LEFT RIGHT     use img convert  RGBA   tobytes   as texels

User · Answer

Python shouldn t crash when you call getdata    The image might be corrupted or there is something wrong with your PIL installation  Try it with another image or post the image you are using   This should break down the image the way you want   from PIL import Image im   Image open  um 000000 png    pixels   list im getdata    width  height   im size pixels    pixels i   width  i   1    width  for i in xrange height

User · Answer

Not PIL  but scipy misc imread might still be interesting   import scipy misc im   scipy misc imread  um 000000 png   flatten False  mode  RGB   print im shape    gives   480  640  3    so it is  height  width  channels   So you can iterate over it by  for y in range im shape 0        for x in range im shape 1            color   tuple im y  x           r  g  b   color

User · Answer

If you have numpy installed you can try   data   numpy asarray im     I say  try  here  because it s unclear why getdata   isn t working for you  and I don t know whether asarray uses getdata  but it s worth a test

User · Answer

Or if you want to count white or black pixels  This is also a solution   from PIL import Image import operator  img   Image open  your file png   convert  1   black  white   img getcolors    print black 0  print white 0

[python] Getting list of pixel values from PIL

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