App Engine 裁剪为特定宽度和高度

Question

我需要调整图像大小并将图像裁剪为特定的宽度和高度。我能够构造一种方法来创建方形缩略图，但当所需的缩略图不是方形时，我不确定如何应用它。

def rescale(data, width, height):
"""Rescale the given image, optionally cropping it to make sure the result image has the specified width and height."""
from google.appengine.api import images

new_width = width
new_height = height

img = images.Image(data)

org_width, org_height = img.width, img.height

# We must determine if the image is portrait or landscape
# Landscape
if org_width > org_height:
    # With the Landscape image we want the crop to be centered. We must find the
    # height to width ratio of the image and Convert the denominater to a float
    # so that ratio will be a decemal point. The ratio is the percentage of the image
    # that will remain.
    ratio = org_height / float(org_width)
    # To find the percentage of the image that will be removed we subtract the ratio
    # from 1 By dividing this number by 2 we find the percentage that should be
    # removed from each side this is also our left_x coordinate
    left_x = (1- ratio) / 2
    # By subtract the left_x from 1 we find the right_x coordinate
    right_x = 1 - left_x
    # crop(image_data, left_x, top_y, right_x, bottom_y), output_encoding=images.PNG)
    img.crop(left_x, 0.0, right_x, 1.0)
    # resize(image_data, width=0, height=0, output_encoding=images.PNG)
    img.resize(height=height)
# Portrait
elif org_width < org_height:
    ratio = org_width / float(org_height)
    # crop(image_data, left_x, top_y, right_x, bottom_y), output_encoding=images.PNG)
    img.crop(0.0, 0.0, 1.0, ratio)
    # resize(image_data, width=0, height=0, output_encoding=images.PNG)
    img.resize(width=witdh)

thumbnail = img.execute_transforms()
return thumbnail

如果有更好的方法来做到这一点，请告诉我。任何帮助将不胜感激。

这是解释所需过程的图表。

谢谢，

凯尔

Answer 1

我遇到了类似的问题（你的屏幕截图非常有用）。这是我的解决方案：

def rescale(img_data, width, height, halign='middle', valign='middle'):
  """Resize then optionally crop a given image.

  Attributes:
    img_data: The image data
    width: The desired width
    height: The desired height
    halign: Acts like photoshop's 'Canvas Size' function, horizontally
            aligning the crop to left, middle or right
    valign: Verticallly aligns the crop to top, middle or bottom

  """
  image = images.Image(img_data)

  desired_wh_ratio = float(width) / float(height)
  wh_ratio = float(image.width) / float(image.height)

  if desired_wh_ratio > wh_ratio:
    # resize to width, then crop to height
    image.resize(width=width)
    image.execute_transforms()
    trim_y = (float(image.height - height) / 2) / image.height
    if valign == 'top':
      image.crop(0.0, 0.0, 1.0, 1 - (2 * trim_y))
    elif valign == 'bottom':
      image.crop(0.0, (2 * trim_y), 1.0, 1.0)
    else:
      image.crop(0.0, trim_y, 1.0, 1 - trim_y)
  else:
    # resize to height, then crop to width
    image.resize(height=height)
    image.execute_transforms()
    trim_x = (float(image.width - width) / 2) / image.width
    if halign == 'left':
      image.crop(0.0, 0.0, 1 - (2 * trim_x), 1.0)
    elif halign == 'right':
      image.crop((2 * trim_x), 0.0, 1.0, 1.0)
    else:
      image.crop(trim_x, 0.0, 1 - trim_x, 1.0)

  return image.execute_transforms()

Answer 2

您可以指定 height 和 width 参数来调整 resize ——它不会改变宽高比（您不能使用 GAE 的 images 模块来实现这一点），但它将确保两个维度中的每一个都 <= 您指定的对应值（事实上，一个将完全等于到您指定的值，另一个将为 <=）。

我不确定为什么你要先裁剪然后调整大小 - 似乎你应该以相反的方式做事......调整大小，以便尽可能多的原始图像“适合”可行，然后裁剪以确保精确的结果尺寸。 （因此，如果我正确理解您的要求，您不会使用原始提供的高度和宽度值来调整大小 - 您会将它们放大，这样生成的图像就不会“浪费”，也称为“空白”）。所以也许我不明白你到底需要什么——你能提供一个例子吗（处理前图像的URL、处理后图像的样子，以及你要传递的参数的详细信息） ？