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,filename):
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(self):
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(self._filename)
self._mode=im.mode
self._width,self._height=im.size
for y in range(self._height):
for x in range(self._width):
r,g,b=im.getpixel((x,y))
self._rgblist.append((r,g,b))
pval=self.makepixval((r,g,b))
self._pixellist.append(pval)
self._pixarray=array(self._pixellist,float)

def makergb(self,pixval):
alpha=pixval>>24
red=(pixval>>16 )&255
green=(pixval>>8 )&255
blue=(pixval)& 255
return red,green,blue

def writeImage1(self,fname,data,width,height):
imnew=Image.new(self._mode,(width,height))
newrgblist=[]
for i in range(len(data)):
r,g,b=self.makergb(data[i])
newrgblist.append((r,g,b))
index=0
for y in range(height):
for x in range(width):
imnew.putpixel((x,y),newrgblist[index])
index+=1
imnew.save(fname)

def writeImage2(self,fname,data,width,height):
imnew=Image.new(self._mode,(width,height))
newrgblist=[]
for i in range(len(data)):
r,g,b=self.makergb(data[i])
newrgblist.append((r,g,b))
imnew.putdata(newrgblist)
imnew.save(fname)
imgname=argv[1] #Usage: python jpgpy.py myimage.jpg
print "to read from:",imgname
x=JPGFile(imgname)
print x.getheight(),"",x.getwidth()
pixlist=x.getpixellist()
rgbtpllist=x.getrgblist()
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.com 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,filename):
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(self):
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(self._filename)
self._mode=im.mode
self._width,self._height=im.size
for y in range(self._height):
for x in range(self._width):
r,g,b=im.getpixel((x,y))
self._rgblist.append((r,g,b))
pval=self.makepixval((r,g,b))
self._pixellist.append(pval)
self._pixarray=array(self._pixellist,float)

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

def makergb(self,pixval):
alpha=pixval>>24
red=(pixval>>16 )&255
green=(pixval>>8 )&255
blue=(pixval)& 255
return red,green,blue

Again a simple function.

def writeImage1(self,fname,data,width,height):
imnew=Image.new(self._mode,(width,height))
newrgblist=[]
for i in range(len(data)):
r,g,b=self.makergb(data[i])
newrgblist.append((r,g,b))

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

for pixval in data:
rgb = pixval2rgb(pixval)
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..will try to improve it
again many thanx
dn