Nathan Horne – Technical Artist

Couldn’t find any good examples of directly writing to the QImage bits without using numpy, so here’s a simple example 🙂 (PyQt)

This just accesses the image bits uchar* directly, and uses struct.pack to convert the qRgb values into bytes for the uchar * (via sip.voidptr)

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<pre>import struct
from PyQt4 import QtGui

#initialize the QImage
img = QtGui.QImage(512, 512, QtGui.QImage.Format_RGB32)
#Build the color object up front, new QColor every pixel is SLOW!
color = QtGui.QColor()

#Initialize the sip uchar ptr
ucharptr = img.bits()
ucharptr.setsize(img.byteCount())

i = 0
w = float(img.width())
h = float(img.height())
halfw = w/2

for y in range(img.height()):
	for x in range(img.width()):
		hue = (y/h)*360
		if x<halfw:
			sat = (x/halfw)*255
			val = 255
		else:
			sat = 255
			val = 255 - (((x-halfw)/halfw)*255)

		#Set the color values as HSV, then convert to qRgb
		color.setHsv(hue, sat, val)

		#Pack the qRgb into bytes using struct
		#Each pixel is 4 bytes, write the slice
		ucharptr[i:i+4] = struct.pack('I', color.rgb())
		i+=4

img.save('c:/out.png')

Result should look like Maya’s spectrum color picker

(And yes, QImage.setPixel does work as an alternative, but speed is worse, and even the QImage documentation recommends avoiding it)