PIL：放大图像

Question

我在使用PIL（Python图像库）放大图片时遇到了问题。大图片可以很好地缩小，但小图片却无法放大。

# get the ratio of the change in height of this image using the
# by dividing the height of the first image
s = h / float(image.size[1])
# calculate the change in dimension of the new image
new_size = tuple([int(x*s) for x in image.size])
# if this image height is larger than the image we are sizing to
if image.size[1] > h: 
    # make a thumbnail of the image using the new image size
    image.thumbnail(new_size)
    by = "thumbnailed"
    # add the image to the images list
    new_images.append(image)
else:
    # otherwise try to blow up the image - doesn't work
    new_image = image.resize(new_size)
    new_images.append(new_image)
    by = "resized"
logging.debug("image %s from: %s to %s" % (by, str(image.size), str(new_size)))

Answer 1

这里有一个使用openCV和numpy来调整图像大小的示例，能够在各个方向上进行调整：

import cv2, numpy

original_image = cv2.imread('original_image.jpg',0)
original_height, original_width = original_image.shape[:2]
factor = 2
resized_image = cv2.resize(original_image, (int(original_height*factor), int(original_width*factor)), interpolation=cv2.INTER_CUBIC )

cv2.imwrite('resized_image.jpg',resized_image)
#fixed var name

就是这么简单。如果你想放大图片（放大倍数大于1），可以使用“cv2.INTER_CUBIC”；如果想缩小图片（放大倍数小于1），则可以使用“cv2.INTER_AREA”。

Answer 2

这段话的意思是，resize 和 transform 这两个方法都可以正确地调整图片的大小。

size_tuple = im.size
x1 = y1 = 0
x2, y2 = size_tuple

# resize
im = im.resize(size_tuple)

# transform
im = im.transform(size_tuple, Image.EXTENT, (x1,y1,x2,y2))

如果你遇到了我之前说的问题，可以试试在另一台电脑上运行。可能是我服务器上的Python安装出了问题，因为在我本地的电脑上运行得很好。