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()