縮放圖片畫布大小

想要縮放圖片的畫布大小,但直接使用 PIL 的 expand() 也會一併放大和縮小圖片內容。

PIL.ImageOps.expand(imageborder=0fill=0)[source]

Add border to the imageParameters

  • image – The image to expand.
  • border – Border width, in pixels.
  • fill – Pixel fill value (a color value). Default is 0 (black).

Returns

An image.

上面第二個參數,可以比照 crop 傳入要 expand 的大小。

最佳解法,是服用下面的函數:

#!/usr/bin/env python

from PIL import Image
import math


def resize_canvas(old_image_path="314.jpg", new_image_path="save.jpg",
                  canvas_width=500, canvas_height=500):
    """
    Resize the canvas of old_image_path.

    Store the new image in new_image_path. Center the image on the new canvas.

    Parameters
    ----------
    old_image_path : str
    new_image_path : str
    canvas_width : int
    canvas_height : int
    """
    im = Image.open(old_image_path)
    old_width, old_height = im.size

    # Center the image
    x1 = int(math.floor((canvas_width - old_width) / 2))
    y1 = int(math.floor((canvas_height - old_height) / 2))

    mode = im.mode
    if len(mode) == 1:  # L, 1
        new_background = (255)
    if len(mode) == 3:  # RGB
        new_background = (255, 255, 255)
    if len(mode) == 4:  # RGBA, CMYK
        new_background = (255, 255, 255, 255)

    newImage = Image.new(mode, (canvas_width, canvas_height), new_background)
    newImage.paste(im, (x1, y1, x1 + old_width, y1 + old_height))
    newImage.save(new_image_path)

resize_canvas()

上面的解法會多2次 FILE I/O, 分別多 read/write 一次,也可以讓input/output 使用 PIL 物件傳遞:

def resize_canvas(im, canvas_width, canvas_height):
    old_width, old_height = im.size
    # Center the image
    x1 = int(math.floor((canvas_width - old_width) / 2))
    y1 = int(math.floor((canvas_height - old_height) / 2))
    mode = im.mode
    if len(mode) == 1:  # L, 1
        new_background = (255)
    if len(mode) == 3:  # RGB
        new_background = (255, 255, 255)
    if len(mode) == 4:  # RGBA, CMYK
        new_background = (255, 255, 255, 255)
    newImage = Image.new(mode, (canvas_width, canvas_height), new_background)
    newImage.paste(im, (x1, y1, x1 + old_width, y1 + old_height))
    return newImage

相關文章

In Python, Python Image Library 1.1.6, how can I expand the canvas without resizing?
https://stackoverflow.com/questions/1572691/in-python-python-image-library-1-1-6-how-can-i-expand-the-canvas-without-resiz

How to Resize, Pad Image to Square Shape and Keep Its Aspect Ratio in Python
https://jdhao.github.io/2017/11/06/resize-image-to-square-with-padding/

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