def scale_image(data, width=60, height=80, compression_quality=70, as_png=False, preserve_aspect_ratio=True):
''' Scale an image, returning it as either JPEG or PNG data (bytestring).
Transparency is alpha blended with white when converting to JPEG. Is thread
safe and does not require a QApplication. '''
# We use Qt instead of ImageMagick here because ImageMagick seems to use
# some kind of memory pool, causing memory consumption to sky rocket.
if isinstance(data, QImage):
img = data
else:
img = QImage()
if not img.loadFromData(data):
raise ValueError('Could not load image for thumbnail generation')
if preserve_aspect_ratio:
scaled, nwidth, nheight = fit_image(img.width(), img.height(), width, height)
if scaled:
img = img.scaled(nwidth, nheight, Qt.KeepAspectRatio, Qt.SmoothTransformation)
else:
if img.width() != width or img.height() != height:
img = img.scaled(width, height, Qt.IgnoreAspectRatio, Qt.SmoothTransformation)
if not as_png and img.hasAlphaChannel():
nimg = QImage(img.size(), QImage.Format_RGB32)
nimg.fill(Qt.white)
p = QPainter(nimg)
p.drawImage(0, 0, img)
p.end()
img = nimg
ba = QByteArray()
buf = QBuffer(ba)
buf.open(QBuffer.WriteOnly)
fmt = 'PNG' if as_png else 'JPEG'
if not img.save(buf, fmt, quality=compression_quality):
raise ValueError('Failed to export thumbnail image to: ' + fmt)
return img.width(), img.height(), ba.data()
def scale_image(data,
width=60,
height=80,
compression_quality=70,
as_png=False,
preserve_aspect_ratio=True):
''' Scale an image, returning it as either JPEG or PNG data (bytestring).
Transparency is alpha blended with white when converting to JPEG. Is thread
safe and does not require a QApplication. '''
# We use Qt instead of ImageMagick here because ImageMagick seems to use
# some kind of memory pool, causing memory consumption to sky rocket.
if isinstance(data, QImage):
img = data
else:
img = QImage()
if not img.loadFromData(data):
raise ValueError('Could not load image for thumbnail generation')
if preserve_aspect_ratio:
scaled, nwidth, nheight = fit_image(img.width(), img.height(), width,
height)
if scaled:
img = img.scaled(nwidth, nheight, Qt.KeepAspectRatio,
Qt.SmoothTransformation)
else:
if img.width() != width or img.height() != height:
img = img.scaled(width, height, Qt.IgnoreAspectRatio,
Qt.SmoothTransformation)
if not as_png and img.hasAlphaChannel():
nimg = QImage(img.size(), QImage.Format_RGB32)
nimg.fill(Qt.white)
p = QPainter(nimg)
p.drawImage(0, 0, img)
p.end()
img = nimg
ba = QByteArray()
buf = QBuffer(ba)
buf.open(QBuffer.WriteOnly)
fmt = 'PNG' if as_png else 'JPEG'
if not img.save(buf, fmt, quality=compression_quality):
raise ValueError('Failed to export thumbnail image to: ' + fmt)
return img.width(), img.height(), ba.data()
