PyQt code to draw image from raw data?

[StevenB]

I'm trying to write PyQt code equivalent to the following C++ code, but I'm stuck. I'm relatively new to Python, and I'm having a hard time following the PyQt documentation for QImage.
I can create the GUI parts, but how do I set up the raw data and call the QImage constructor?

int main(int argc, char* argv[])
{
	// Create the Qt application and GUI components
	QApplication app(argc, argv);
	QMainWindow win;
	QGraphicsScene canvas;
	QGraphicsView view(&canvas, &win);
 
	unsigned char* imageData = new unsigned char[324];
 
	// Generate some image data
	for(int i = 0; i < 324; i++)
	{
		imageData[i] = i % 250;
	}
 
	// Create the colormap for the indexed image
	QVector<QRgb> colormap;
	for(int i = 0; i < 255; i++)
	{
		colormap.append(qRgb(i, i, i));
	}
 
	QImage img(imageData, 18, 18, QImage::Format_Indexed8);	// Create the image
	img.setColorTable(colormap); // Set up the colormap 
	QPixmap pix = QPixmap::fromImage(img); // Convert it to a pixmap so we can display it
	canvas.addPixmap(pix); // Add the pixmap to the graphics canvas
 
	win.show();
	app.exec();
}

int main(int argc, char* argv[])
{
	// Create the Qt application and GUI components
	QApplication app(argc, argv);
	QMainWindow win;
	QGraphicsScene canvas;
	QGraphicsView view(&canvas, &win);

	unsigned char* imageData = new unsigned char[324];

	// Generate some image data
	for(int i = 0; i < 324; i++)
	{
		imageData[i] = i % 250;
	}

	// Create the colormap for the indexed image
	QVector<QRgb> colormap;
	for(int i = 0; i < 255; i++)
	{
		colormap.append(qRgb(i, i, i));
	}

	QImage img(imageData, 18, 18, QImage::Format_Indexed8);	// Create the image
	img.setColorTable(colormap); // Set up the colormap 
	QPixmap pix = QPixmap::fromImage(img); // Convert it to a pixmap so we can display it
	canvas.addPixmap(pix); // Add the pixmap to the graphics canvas

	win.show();
	app.exec();
}

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Here's the Python code I've got so far:

from PyQt4.QtGui import *
from os import sys
 
app = QApplication(sys.argv)
 
# Create the window and the graphics view
win = QMainWindow()
canvas = QGraphicsScene()
view = QGraphicsView(canvas, win)
view.resize(200, 200)
 
# Create the image data - How?
# Create the QImage - How?
 
# Create the colormap
 
pixmap = QPixmap.fromImage(img)
 
# Add the image to the canvas
canvas.addPixmap(pixmap)
 
win.show()
sys.exit(app.exec_())

from PyQt4.QtGui import *
from os import sys

app = QApplication(sys.argv)

# Create the window and the graphics view
win = QMainWindow()
canvas = QGraphicsScene()
view = QGraphicsView(canvas, win)
view.resize(200, 200)

# Create the image data - How?
# Create the QImage - How?

# Create the colormap

pixmap = QPixmap.fromImage(img)

# Add the image to the canvas
canvas.addPixmap(pixmap)

win.show()
sys.exit(app.exec_())

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[MTK358]

Something like this, maybe?

imageData = []
 
for i in range(0, 324):
	imageData[i] = i % 250
 
colormap = []
 
for i in range(0, 255):
	colormap.append(qRgb(i, i, i))
 
img = QImage(imageData, 18, 18, Format_Indexed8)
img.setColorTable(colormap);

imageData = []

for i in range(0, 324):
	imageData[i] = i % 250

colormap = []

for i in range(0, 255):
	colormap.append(qRgb(i, i, i))

img = QImage(imageData, 18, 18, Format_Indexed8)
img.setColorTable(colormap);

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[StevenB]

Unfortunately, it doesn't seem to be that easy.

When I run the line img = QImage(imageData, 10, 10, QImage.Format_Indexed8), I get a bunch of errors saying that the arguments provided don't match any overloaded constructor:

QImage(sip.voidptr, int, int, QImage.Format): argument 1 has unexpected type 'list'
QImage(str, int, int, int, QImage.Format): argument 1 has unexpected type 'list'
QImage(sip.voidptr, int, int, int, QImage.Format): argument 1 has unexpected type 'list'
etc.

QImage(sip.voidptr, int, int, QImage.Format): argument 1 has unexpected type 'list'
QImage(str, int, int, int, QImage.Format): argument 1 has unexpected type 'list'
QImage(sip.voidptr, int, int, int, QImage.Format): argument 1 has unexpected type 'list'
etc.

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I think I need to do something with a "sip.voidptr", but it appears that's essentially just a C++ interface, and not something I can really work with in Python - is that correct?

[MTK358]

I think I need to do something with a "sip.voidptr", but it appears that's essentially just a C++ interface, and not something I can really work with in Python - is that correct?

I don't know much about bindings, maybe someone else can help.

[chenna]

Okay, firstly where are you getting this image data from? Is it a SWIGPy object?
I had the same problem a couple of days where I had a python binding for my camera driver library and the only way of getting image data was an unsigned char*. Which obviously cannot be understood by python because SWIG did the binding.
So when I access my unsigned char* image data directly in python here's what I get:
<Swig Object of type 'unsigned char *' at 0xb77b0bd8>
Anyways i wrote a small interface code to convert any unsigned char* image data to PIL image. which you can convert to QImage using ImageQt
Here's the link to the code
http://www.optionsbender.com/technol...datatopilimage
and a similar post
http://stackoverflow.com/questions/3...mage-to-python

[dbzhang800]

I found a solution:

#!/usr/bin/env python
# -*- coding: UTF-8 -*-
 
import sys
import ctypes
from PyQt4 import QtGui, QtCore
import sip
 
'''
2009-2010 dbzhang800@gmail.com
''' 
 
class Window(QtGui.QWidget):
    def __init__(self, parent=None):
        super(Window, self).__init__(parent)
        self.label = QtGui.QLabel(self)
        self.label.setMinimumSize(512, 512)
        self.comboBox = QtGui.QComboBox(self)
        self.comboBox.addItems(["Image.{}".format(i) for i in range(2)])
        vbox = QtGui.QVBoxLayout(self)
        vbox.addWidget(self.label)
        vbox.addWidget(self.comboBox)
        self.initImages()
        self.comboBox.currentIndexChanged.connect(self.onCurrentIndexChanged)
 
    def onCurrentIndexChanged(self, index):
        self.label.setPixmap(QtGui.QPixmap.fromImage(self.images[index]))
 
    def initImages(self):
        self.images = []
        self.colorTable = [QtGui.qRgb(i, i, i) for i in range(256)]
        self.createImage0()
        self.createImage1()
        self.label.setPixmap(QtGui.QPixmap.fromImage(self.images[0]))
 
    def createImage0(self):
        '''Create an QImage object, the copy data from other buffer to the image buffer.
        '''
        image = QtGui.QImage(512, 512,  QtGui.QImage.Format_Indexed8)
        image.setColorTable(self.colorTable)
        buff = ctypes.create_string_buffer('\xFF'*512*16, 512*16)
        buff2 = ctypes.create_string_buffer('\x1f'*512*32, 512*32)
        img_ptr = image.bits()
        ctypes.memmove(int(img_ptr),  buff,  buff._length_)
        ctypes.memmove(int(img_ptr)+buff._length_,  buff2,  buff2._length_)
        ctypes.memmove(int(img_ptr)+buff._length_+buff2._length_,  buff,  buff._length_)
        self.images.append(image)
 
    def createImage1(self):
        '''we already have a buffer, create an QImage object using the buffer. 
        '''
        self.buff = ctypes.create_string_buffer('\x7F'*512*512)
        image = QtGui.QImage(sip.voidptr(ctypes.addressof(self.buff)), 512, 512,  QtGui.QImage.Format_Indexed8)
        image.setColorTable(self.colorTable)
        self.images.append(image)
 
if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    w = Window()
    w.show()
    sys.exit(app.exec_())

#!/usr/bin/env python
# -*- coding: UTF-8 -*-

import sys
import ctypes
from PyQt4 import QtGui, QtCore
import sip

'''
2009-2010 dbzhang800@gmail.com
''' 

class Window(QtGui.QWidget):
    def __init__(self, parent=None):
        super(Window, self).__init__(parent)
        self.label = QtGui.QLabel(self)
        self.label.setMinimumSize(512, 512)
        self.comboBox = QtGui.QComboBox(self)
        self.comboBox.addItems(["Image.{}".format(i) for i in range(2)])
        vbox = QtGui.QVBoxLayout(self)
        vbox.addWidget(self.label)
        vbox.addWidget(self.comboBox)
        self.initImages()
        self.comboBox.currentIndexChanged.connect(self.onCurrentIndexChanged)

    def onCurrentIndexChanged(self, index):
        self.label.setPixmap(QtGui.QPixmap.fromImage(self.images[index]))
        
    def initImages(self):
        self.images = []
        self.colorTable = [QtGui.qRgb(i, i, i) for i in range(256)]
        self.createImage0()
        self.createImage1()
        self.label.setPixmap(QtGui.QPixmap.fromImage(self.images[0]))
    
    def createImage0(self):
        '''Create an QImage object, the copy data from other buffer to the image buffer.
        '''
        image = QtGui.QImage(512, 512,  QtGui.QImage.Format_Indexed8)
        image.setColorTable(self.colorTable)
        buff = ctypes.create_string_buffer('\xFF'*512*16, 512*16)
        buff2 = ctypes.create_string_buffer('\x1f'*512*32, 512*32)
        img_ptr = image.bits()
        ctypes.memmove(int(img_ptr),  buff,  buff._length_)
        ctypes.memmove(int(img_ptr)+buff._length_,  buff2,  buff2._length_)
        ctypes.memmove(int(img_ptr)+buff._length_+buff2._length_,  buff,  buff._length_)
        self.images.append(image)

    def createImage1(self):
        '''we already have a buffer, create an QImage object using the buffer. 
        '''
        self.buff = ctypes.create_string_buffer('\x7F'*512*512)
        image = QtGui.QImage(sip.voidptr(ctypes.addressof(self.buff)), 512, 512,  QtGui.QImage.Format_Indexed8)
        image.setColorTable(self.colorTable)
        self.images.append(image)

if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    w = Window()
    w.show()
    sys.exit(app.exec_())

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