图像到极坐标

Question

我在将图像转换为极坐标时遇到问题。在 Photoshop 中这很简单 :) 所以这对我来说是一个新领域。

我有以下图片：

它最终应该是这样的：

我已经看过here 并且我已经掌握了基础知识，但仍然对方形圆圈有点困惑：

import math
from PIL import Image, ImageDraw


# image size
imgX = 200
imgY = 200

image = Image.new("RGB", (imgX, imgY))
draw = ImageDraw.Draw(image)

#fill with white first
colour = "#ffffff"
box = [0,0, imgX, imgY]
image.paste(colour, box)

# draw line near base
draw.line((0,180, 200, 180), fill="#FF0000", width=2)

print "Line done!"
image.save("line.png", "PNG")

# there's got to be a way to get the current image
# without having to open it up again

im = Image.open("line.png")
rgb_im = im.convert("RGB")

# rectangle to polar coordinates
maxradius = math.sqrt(imgX**2 + imgY**2)/2
rscale = imgX / maxradius
tscale = imgY / (2*math.pi)

for y in range(0, imgY):
    dy = y - imgY/2

    for x in range(0, imgX):
        dx = x - imgX/2
        t = math.atan2(dy,dx)%(2*math.pi)
        r = math.sqrt(dx**2+dy**2)

        r, g, b = rgb_im.getpixel((x, y))
        # this is where it goes wrong
        col = b * 65536 + g * 256 + r
        image.putpixel((x, y), b * 65536 + g * 256 + r

image.save("polar.png", "PNG")

我几乎对如何重绘图像有点困惑。还有一个警告：由于管理限制，我想避免使用像 Numpy 这样的外部库。

Answer 1

以下代码对我有用。主要变化：

• 为line_image 和circle_image 创建了单独的变量。没有理由重新加载图像，您可以重复使用line_image...

• t 和 r 将为您提供要在线条图像中访问的图像坐标，用于圆图像中每个对应的 x 和 y。它们已经存在，您只需有效地将它们用作索引来获取像素颜色。

• 将rscale 和tscale 应用到r 和t，使2×pi 对应于图像的右边缘。您肯定需要更改 r 的比例，以便能够在输出中看到这个圆圈，或者将线画得更接近顶部（例如，在第 100 行而不是 180 行）。

  李>

• 我还为行图像访问添加了边界检查。

```

import math
from PIL import Image, ImageDraw     
# image size
imgX = 200
imgY = 200

line_image = Image.new("RGB", (imgX, imgY))
draw = ImageDraw.Draw(line_image)

#fill with white first
colour = "#ffffff"
box = [0,0, imgX, imgY]
line_image.paste(colour, box)

# draw line near base
draw.line((0,180, 200, 180), fill="#FF0000", width=2)

print "Line done!"
line_image.save("line.png", "PNG")

circle_image = Image.new("RGB", (imgX, imgY))

# rectangle to polar coordinates
maxradius = math.sqrt(imgX**2 + imgY**2)/2
rscale = imgX / maxradius
tscale = imgY / (2*math.pi)

for y in range(0, imgY):
    dy = y - imgY/2

    for x in range(0, imgX):
        dx = x - imgX/2
        t = math.atan2(dy,dx)%(2*math.pi)*tscale
        r = math.sqrt(dx**2+dy**2)*rscale

        if 0<= t < imgX and 0 <= r < imgY:
            r, g, b = line_image.getpixel((t, r))
            # this is where it goes wrong
            col = b * 65536 + g * 256 + r
            circle_image.putpixel((x, y), col)

circle_image.save("polar.png", "PNG")

```