do i need to create new rgbimage class

[Gabriel Genellina]

On 29 dic, 12:42, jimgarde... at gmail.com wrote:

> am a beginner in python and PIL  .I need to read an RGB 8 bit image
> (am using jpeg )and pack the rgb color values into a double value so i
> can store the image as a list of pixelvalues.From my application i
> should be able to call rgbimage1.getpixellist() to retrieve the double
> values of an image.

(May I ask why an accessor like getpixellist() instead of simply
rgbimage1.pixellist?)

> Do i need to create a new class for this?I made something like
>
> class myrgbimage:
>       def  __init__(self,filename):
>
>       def _readimage(self):
>           im=Image.open(filename)
>           self._readImage(filename)
>           self._wd,self._ht=im.size
>           for y in range(self._ht):
>                for x in range(self._wd):
>                      r,g,b=im.getpixel((x,y))
>                      pval=self.rgbTodoubleval((r,g,b))
>                      self._pixellist.append(pval)

The PIL docs at [1] say that using getpixel is very slow, and suggest
to use getdata instead. And you want a flat representation anyway,
just like getdata. So replace the for loops above with:

          rgbTodoubleval = self.rgbTodoubleval
          self._pixellist = [rgbTodoubleval(pix) for pix in
im.getdata()]

I've not tested it, but should be faster.

>       def rgbTodoubleval(self,(r,g,b)):
>           alpha=255
>           pixelvalue=(alpha<<24)|(r<<16 )|( g<<8) | b
>           return pixelvalue

I don't get the name - why "rgb to double"? This does not return a
"double", but a long integer, even if you intended to return a 32 bit
integer.
This version returns an integer:

from struct import pack, unpack
def rgbTodoubleval((r,g,b)):
  alpha=255
  return unpack("l", pack("BBBB", b, g, r, alfa))[0]

It *may*, or not, be what you want...

--
Gabriel Genellina