[Image-SIG] Re: Returning Colormap values for an image?

[Alfred Milgrom]

Thank you for your prompt answer to my problem. I am sorry to trouble
you further.

Unfortunately I think I am missing something as far as the
resize/convert technique is concerned. Basically I do not understand
why all the colours will be preserved if the image is resized, nor why
the colours will then be neatly arranged in the lut Image.

I have adapted my colourinfo function to use the resize/convert
technique, but I only get two different colours in the resulting
256-pixel image instead of 6.

I get the same difference in results from either the grabbed image or
the saved image.
Not only that, but I get different number of colours and colours after
I convert the image to P mode.

I would be grateful if you could point out what I am doing wrong.

Thanks in advance,
Alfred Milgrom

########################################################
# Test of colour palette returned from ImageGrab

from Tkinter import *
import ImageGrab
import Image
import os

class GUI (Frame):
    top = Tk()
    
    def __init__(self, parent=top):
        Frame.__init__(self,parent)
        self.master.title('Grab Test')
        self.Board = Canvas(self, width=200 , height=200 , bg="#FFF000")
        self.Board.pack(side=TOP, padx=10, pady=10)
        fButtons = Frame(self)
        self.bGrab = Button(fButtons, width=15, text="Grab",
command=self.grabBoard)
        self.bGrab.pack(side=LEFT, anchor=W, padx=10, pady=2)
        self.bQuit = Button(fButtons, width=15, text="Quit",
command=self.top.destroy)
        self.bQuit.pack(side=LEFT, anchor=W, padx=10, pady=2)
        fButtons.pack(side=BOTTOM, fill=X)
        self.pack()

        self.Board.create_rectangle(70, 70, 90, 90, fill='white')

    def colourinfo(self, im):
        hist = im.histogram()

        coloursUsed = len([x for x in hist if x])
        print "There are %s colours in this image" %coloursUsed
        
        print "Colours using resize/convert colours method:"
        lut = im.resize((256,1)).convert("RGB").getdata()
        print [x for x in lut if x not in locals()['_[1]'].__self__]
        print "Colours using all data"
        lut = im.convert("RGB").getdata()
        print [x for x in lut if x not in locals()['_[1]'].__self__]

    def grabBoard(self):
        x0 = self.Board.winfo_rootx()+2
        y0 = self.Board.winfo_rooty()+2
        x1 = x0 + 100
        y1 = y0 + 100
        im = ImageGrab.grab((x0, y0, x1, y1))
        print "The grabbed image is in %s mode" %im.mode
        self.colourinfo(im)

        im = im.convert('P')
        print "\nThe grabbed image is now in %s mode" %im.mode
        self.colourinfo(im)
        
        path = os.getcwd()
        im.save(os.path.join(path, 'mytest.gif'))

        im2 = Image.open(os.path.join(path, 'mytest.gif'))
        print "\nInformation from saved image:"
        self.colourinfo(im2)

if __name__ == "__main__":
    board = GUI()



On Wed, 11 Aug 2004 15:34:59 +0200, Fredrik Lundh
<fredrik at pythonware.com> wrote:
> Alfred Milgrom wrote:
> 
> > How can I get the correct data from the grabbed image without having
> > to save it first?
> 
> the palette string may have different formats depending on the
> data source (the palette.rawmode attribute is used to describe
> the actual format).
> 
> instead of peeking into the palette object, use the resize/convert
> technique described in this message:
> 
> 
> 
>     http://article.gmane.org/gmane.comp.python.general/347330
> 
> </F>
> 
> _______________________________________________
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