Convert RGBA PNG to RGB with PIL

Question

I m using PIL to convert a transparent PNG image uploaded with Django to a JPG file  The output looks broken   Source file    Code  Image open object logo path  save   tmp output jpg    JPEG     or  Image open object logo path  convert  RGB   save   tmp output png     Result  Both ways  the resulting image looks like this     Is there a way to fix this  I d like to have white background where the transparent background used to be     Solution  Thanks to the great answers  I ve come up with the following function collection   import Image import numpy as np   def alpha to color image  color  255  255  255           Set all fully transparent pixels of an RGBA image to the specified color      This is a very simple solution that might leave over some ugly edges  due     to semi-transparent areas  You should use alpha composite with color instead       Source  http   stackoverflow com a 9166671 284318      Keyword Arguments      image -- PIL RGBA Image object     color -- Tuple r  g  b  default 255  255  255                x   np array image      r  g  b  a   np rollaxis x  axis -1      r a    0    color 0      g a    0    color 1      b a    0    color 2       x   np dstack  r  g  b  a       return Image fromarray x   RGBA     def alpha composite front  back          Alpha composite two RGBA images       Source  http   stackoverflow com a 9166671 284318      Keyword Arguments      front -- PIL RGBA Image object     back -- PIL RGBA Image object              front   np asarray front      back   np asarray back      result   np empty front shape  dtype  float       alpha   np index exp       3       rgb   np index exp        3      falpha   front alpha    255 0     balpha   back alpha    255 0     result alpha    falpha   balpha    1 - falpha      old setting   np seterr invalid  ignore       result rgb     front rgb    falpha   back rgb    balpha    1 - falpha     result alpha      np seterr   old setting      result alpha     255     np clip result  0  255        astype  uint8   maps np nan and np inf to 0     result   result astype  uint8       result   Image fromarray result   RGBA       return result   def alpha composite with color image  color  255  255  255           Alpha composite an RGBA image with a single color image of the     specified color and the same size as the original image       Keyword Arguments      image -- PIL RGBA Image object     color -- Tuple r  g  b  default 255  255  255               back   Image new  RGBA   size image size  color color    255        return alpha composite image  back    def pure pil alpha to color v1 image  color  255  255  255           Alpha composite an RGBA Image with a specified color       NOTE  This version is much slower than the     alpha composite with color solution  Use it only if     numpy is not available       Source  http   stackoverflow com a 9168169 284318      Keyword Arguments      image -- PIL RGBA Image object     color -- Tuple r  g  b  default 255  255  255                def blend value back  front  a           return  front   a   back    255 - a     255      def blend rgba back  front           result    blend value back i   front i   front 3   for i in  0  1  2           return tuple result    255        im   image copy      don t edit the reference directly     p   im load      load pixel array     for y in range im size 1            for x in range im size 0                p x  y    blend rgba color    255    p x  y        return im  def pure pil alpha to color v2 image  color  255  255  255           Alpha composite an RGBA Image with a specified color       Simpler  faster version than the solutions above       Source  http   stackoverflow com a 9459208 284318      Keyword Arguments      image -- PIL RGBA Image object     color -- Tuple r  g  b  default 255  255  255               image load      needed for split       background   Image new  RGB   image size  color      background paste image  mask image split   3      3 is the alpha channel     return background   Performance  The simple non-compositing alpha to color function is the fastest solution  but leaves behind ugly borders because it does not handle semi transparent areas   Both the pure PIL and the numpy compositing solutions give great results  but alpha composite with color is much faster  8 93 msec  than pure pil alpha to color  79 6 msec   If numpy is available on your system  that s the way to go   Update  The new pure PIL version is the fastest of all mentioned solutions      python -m timeit  import Image  from apps front import utils  i   Image open u logo png    i2   utils alpha to color i   10 loops  best of 3  4 67 msec per loop   python -m timeit  import Image  from apps front import utils  i   Image open u logo png    i2   utils alpha composite with color i   10 loops  best of 3  8 93 msec per loop   python -m timeit  import Image  from apps front import utils  i   Image open u logo png    i2   utils pure pil alpha to color i   10 loops  best of 3  79 6 msec per loop   python -m timeit  import Image  from apps front import utils  i   Image open u logo png    i2   utils pure pil alpha to color v2 i   10 loops  best of 3  1 1 msec per loop

User · Answer

Here s a solution in pure PIL   def blend value under  over  a       return  over a   under  255-a     255  def blend rgba under  over       return tuple  blend value under i   over i   over 3   for i in  0 1 2      255    white    255  255  255  255   im   Image open object logo path  p   im load   for y in range im size 1        for x in range im size 0            p x y    blend rgba white  p x y   im save   tmp output png

User · Answer

The transparent parts mostly have RGBA value  0 0 0 0   Since the JPG has no transparency  the jpeg value is set to  0 0 0   which is black   Around the circular icon  there are pixels with nonzero RGB values where A   0  So they look transparent in the PNG  but funny-colored in the JPG   You can set all pixels where A    0 to have R   G   B   255 using numpy like this   import Image import numpy as np  FNAME    logo png  img   Image open FNAME  convert  RGBA   x   np array img  r  g  b  a   np rollaxis x  axis   -1  r a    0    255 g a    0    255 b a    0    255 x   np dstack  r  g  b  a   img   Image fromarray x   RGBA   img save   tmp out jpg         Note that the logo also has some semi-transparent pixels used to smooth the edges around the words and icon  Saving to jpeg ignores the semi-transparency  making the resultant jpeg look quite jagged   A better quality result could be made using imagemagick s convert command   convert logo png -background white -flatten  tmp out jpg       To make a nicer quality blend using numpy  you could use alpha compositing   import Image import numpy as np  def alpha composite src  dst               Return the alpha composite of src and dst       Parameters      src -- PIL RGBA Image object     dst -- PIL RGBA Image object      The algorithm comes from http   en wikipedia org wiki Alpha compositing               http   stackoverflow com a 3375291 190597       http   stackoverflow com a 9166671 190597     src   np asarray src      dst   np asarray dst      out   np empty src shape  dtype    float       alpha   np index exp       3       rgb   np index exp        3      src a   src alpha  255 0     dst a   dst alpha  255 0     out alpha    src a dst a  1-src a      old setting   np seterr invalid    ignore       out rgb     src rgb  src a   dst rgb  dst a  1-src a   out alpha      np seterr   old setting          out alpha     255     np clip out 0 255        astype  uint8   maps np nan  and np inf  to 0     out   out astype  uint8       out   Image fromarray out   RGBA       return out              FNAME    logo png  img   Image open FNAME  convert  RGBA   white   Image new  RGBA   size   img size  color    255  255  255  255   img   alpha composite img  white  img save   tmp out jpg

User · Answer

import numpy as np import PIL  def convert image image file       image   Image open image file    this could be a 4D array PNG  RGBA      original width  original height   image size      np image   np array image      new image   np zeros  np image shape 0   np image shape 1   3          create 3D array      for each channel in range 3           new image     each channel    np image     each channel              only copy first 3 channels         flushing     np image          return new image

User · Answer

Here s a version that s much simpler - not sure how performant it is  Heavily based on some django snippet I found while building RGBA - gt  JPG   BG support for sorl thumbnails    from PIL import Image  png   Image open object logo path  png load     required for png split    background   Image new  RGB   png size   255  255  255   background paste png  mask png split   3     3 is the alpha channel  background save  foo jpg    JPEG   quality 80    Result  80     Result   50

User · Answer

By using Image alpha composite  the solution by Yuji  Tomita  Tomita become simpler  This code can avoid a tuple index out of range error if png has no alpha channel   from PIL import Image  png   Image open img path  convert  RGBA   background   Image new  RGBA   png size   255 255 255    alpha composite   Image alpha composite background  png  alpha composite save  foo jpg    JPEG   quality 80

User · Answer

import Image  def fig2img   fig                 brief Convert a Matplotlib figure to a PIL Image in RGBA format and return it      param fig a matplotlib figure      return a Python Imaging Library   PIL   image               put the figure pixmap into a numpy array     buf   fig2data   fig       w  h  d   buf shape     return Image frombytes   RGBA     w  h    buf tostring       def fig2data   fig                 brief Convert a Matplotlib figure to a 4D numpy array with RGBA channels and return it      param fig a matplotlib figure      return a numpy 3D array of RGBA values               draw the renderer     fig canvas draw        Get the RGBA buffer from the figure w h   fig canvas get width height   buf   np fromstring   fig canvas tostring argb    dtype np uint8   buf shape     w  h  4      canvas tostring argb give pixmap in ARGB mode  Roll the ALPHA channel to have it in RGBA mode buf   np roll   buf  3  axis   2   return buf   def rgba2rgb img  c  0  0  0   path  foo jpg   is already saved False  if load True       if not is already saved          background   Image new  RGB   img size  c          background paste img  mask img split   3     3 is the alpha channel      background save path   JPEG   quality 100         is already saved   True if if load      if is already saved          im   Image open path          return np array im      else          raise ValueError  No image to load

User · Answer

It s not broken  It s doing exactly what you told it to  those pixels are black with full transparency  You will need to iterate across all pixels and convert ones with full transparency to white

[python] Convert RGBA PNG to RGB with PIL

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