jpeg image read class

[devnew]

hi
i am new to python and PIL and was trying to write a class to read and
write RGB color model jpeg images..
i came up with this class below..i want to know if this is the way to
read/write the RGB color model jpeg..if anyone can give feedback (esp
on the methods writeImage1( ) and writeImage2( ) it wd help my
studies ..
TIA
dn

#jpgpy.py

import Image
from sys import argv
from numpy import array
class JPGFile:
def __init__(self,f ilename):
self._filename= filename
self._height=0
self._width=0
self._mode=""
self._rgblist=[]
self._pixellist =[]
self._pixarray= None
self.readImage( )

def getheight(self) :
return self._height
def getwidth(self):
return self._width

def getpixellist(se lf):
return self._pixellist

def getrgblist(self ):
return self._rgblist

def makepixval(self ,(r,g,b)):
alpha=255
pixval=(alpha<< 24)|(r<<16 )|( g<<8) | b
return pixval

def readImage(self) :
im=Image.open(s elf._filename)
self._mode=im.m ode
self._width,sel f._height=im.si ze
for y in range(self._hei ght):
for x in range(self._wid th):
r,g,b=im.getpix el((x,y))
self._rgblist.a ppend((r,g,b))
pval=self.makep ixval((r,g,b))
self._pixellist .append(pval)
self._pixarray= array(self._pix ellist,float)

def makergb(self,pi xval):
alpha=pixval>>2 4
red=(pixval>>16 )&255
green=(pixval>> 8 )&255
blue=(pixval)& 255
return red,green,blue

def writeImage1(sel f,fname,data,wi dth,height):
imnew=Image.new (self._mode,(wi dth,height))
newrgblist=[]
for i in range(len(data) ):
r,g,b=self.make rgb(data[i])
newrgblist.appe nd((r,g,b))
index=0
for y in range(height):
for x in range(width):
imnew.putpixel( (x,y),newrgblis t[index])
index+=1
imnew.save(fnam e)

def writeImage2(sel f,fname,data,wi dth,height):
imnew=Image.new (self._mode,(wi dth,height))
newrgblist=[]
for i in range(len(data) ):
r,g,b=self.make rgb(data[i])
newrgblist.appe nd((r,g,b))
imnew.putdata(n ewrgblist)
imnew.save(fnam e)
imgname=argv[1] #Usage: python jpgpy.py myimage.jpg
print "to read from:",imgname
x=JPGFile(imgna me)
print x.getheight()," ",x.getwidt h()
pixlist=x.getpi xellist()
rgbtpllist=x.ge trgblist()
w=x.getwidth()
h=x.getheight()
x.writeImage1(" newimage1.jpg", pixlist,w,h)

[Marc 'BlackJack' Rintsch]

On Wed, 31 Oct 2007 06:48:18 +0000, de****@gmail.co m wrote:

i am new to python and PIL and was trying to write a class to read and
write RGB color model jpeg images..

PIL already offers such a class.

i came up with this class below..i want to know if this is the way to
read/write the RGB color model jpeg..if anyone can give feedback (esp
on the methods writeImage1( ) and writeImage2( ) it wd help my
studies ..

Those are bad names. What does 1 and 2 mean in them!?

class JPGFile:
def __init__(self,f ilename):
self._filename= filename
self._height=0
self._width=0
self._mode=""

This will always be 'RGB' so why store it?

self._rgblist=[]
self._pixellist =[]
self._pixarray= None

In the end you store the image *three times* in different representations .
Is that really necessary?

self.readImage( )

Is `readImage()` supposed to be called again later? If not you might add
an underscore in front and give the file name as argument. Then you could
drop `self._filename `.

def getheight(self) :
return self._height
def getwidth(self):
return self._width

def getpixellist(se lf):
return self._pixellist

def getrgblist(self ):
return self._rgblist

Maybe get rid of those trivial getters and the underscore in front of the
names. That's a little "unpythonic ". Do a web search for "Python is not
Java".

def makepixval(self ,(r,g,b)):
alpha=255
pixval=(alpha<< 24)|(r<<16 )|( g<<8) | b
return pixval

Looks like an ordinary function to me. `self` is not used.

def readImage(self) :
im=Image.open(s elf._filename)
self._mode=im.m ode
self._width,sel f._height=im.si ze
for y in range(self._hei ght):
for x in range(self._wid th):
r,g,b=im.getpix el((x,y))
self._rgblist.a ppend((r,g,b))
pval=self.makep ixval((r,g,b))
self._pixellist .append(pval)
self._pixarray= array(self._pix ellist,float)

Iterating over `im.getdata()` should be simpler and faster than the nested
loops.

def makergb(self,pi xval):
alpha=pixval>>2 4
red=(pixval>>16 )&255
green=(pixval>> 8 )&255
blue=(pixval)& 255
return red,green,blue

Again a simple function.

def writeImage1(sel f,fname,data,wi dth,height):
imnew=Image.new (self._mode,(wi dth,height))
newrgblist=[]
for i in range(len(data) ):
r,g,b=self.make rgb(data[i])
newrgblist.appe nd((r,g,b))

If you have ``for i in range(len(somet hing)):`` you almost always really
wanted to iterate over `something` directly. That loop can be written as:

for pixval in data:
rgb = pixval2rgb(pixv al)
rgbs.append(rgb )

Or even shorter in one line:

rgbs = map(pixval2rgb, data)

If the `numpy` array is what you want/need it might be more efficient to do
the RGB to "pixval" conversion with `numpy`. It should be faster to shift
and "or" a whole array instead of every pixel one by one in pure Python.

Ciao,
Marc 'BlackJack' Rintsch

[devnew]

Marc
thanx for the reply..it wd help me to write better code..i was trying
to learn PIL and python and may be my java background made it
unpythonic..wil l try to improve it
again many thanx
dn