Load blob image data into QPixmap

Question

I am writing a program using PyQt4 for front-end GUI and this program accesses a back-end database (which can be either MySQL or SQLite). I need to store some image data in the database and below is the Python code I use to import image files (in JPEG format) to a blob data field in the database:

def dump_image(imgfile):
    i = open(imgfile, 'rb')
    i.seek(0)
    w = i.read()
    i.close()
    return cPickle.dumps(w,1)
blob = dump_image(imgfile)
hex_str = blob.encode('hex') 
# x"%s"%hex_str will be the string inserted into the SQL command

This part works fine. My question is about how to create a QPixmap object from the image data stored in the database in PyQt4. My current approach involves the following steps:

(1) Hex str in database -- cPickle&StringIO --> PIL Image Object

def load_image(s):
    o = cPickle.loads(s)
    c = StringIO.StringIO()
    c.write(o)
    c.seek(0)
    im = Image.open(c)
    return im

(2) PIL Image Object -->Temporary image file

(3) Temporary image file --> QPixmap

This approach also works fine. But it would be better if I don't have to write/read temporary image files which may slow down the program response to user interactions. I guess I could use QPixmap::loadFromData() to directly load from the blob data stored in the database and hope someone here could show me an example on how to use this function.

TIA,

Bing

Solution 1

You can use the QImage.fromData static method to load an image from a string and then convert it to a pixmap:

 image_data = get_image_data_from_blob()
 qimg = QtGui.QImage.fromData(image_data)
 pixmap = QtGui.QPixmap.fromImage(qimg)

Solution 2

The approach suggested by Ants Aasma works and actually it is also OK to just use the following code:

image_data = cPickle.loads(str(s)) # s is fetched from DB 
qp = QPixmap() 
qp.loadFromData(image_data) 

Thanks a lot for all the help and information.

Comments

[balpha]

Why do you even use the PIL step? Qt is perfectly happy with loading JPEG data: docs.huihoo.com/pyqt/pyqt4/html/…

[Tara]

I am sure Qt is able to load JPEG data. What I am looking for is a code snippet that converts the string encoded in the blob field to the QPixmap object. Thanks!

[Tara]

I figured out I can just use QPixmap::loadFromData(cPickle.loads(s)) where s is the string data fetched from the blob field. Thanks for the help.