python - 如何将图像分成大小均匀、需要时重叠的图 block ？

Question

我有一张图像，其高度/宽度尺寸分别为 3837x5126 像素。

我的目标是将此图像分成具有 1000x1000 像素精确尺寸的独立图 block 。如果图像不能被均匀分割，则应创建重叠图 block ，使图 block 均为 1000x1000 像素。

这是在 PowerPoint 中创建的粗略可视化，用于说明我正在尝试做的事情:

我的思考过程是这样的:

1. 将图像除以我的理想尺寸 (1000)
2. 记下余数
3. 通过将余数除以所有除法来创建偏移量
4. 对于每个分区，减去偏移量
5. 以 1000x1000 的尺寸创建重叠图 block 。

---

这是我到目前为止的代码。

import numpy as np

def get_divisions(num, divisor):
    n = num / divisor
    divisions = math.floor(n)
    remainder = n % 1
    offset = remainder / divisions

    return divisions, offset


def get_tiles(height, width, window_size=1000):
    number_of_rows, row_offset   = get_divisions(height, window_size)
    number_of_columns, col_offet = get_divisions(width, window_size)


    tiles = []
    for row in range(number_of_rows):
        for col in range(number_of_columns):
            if row == 0:
                row_offset = 0

            if col == 0:
                col_offset = 0

            x = (col * window_size) - (col_offset * window_size)
            y = (row * window_size) - (row_offset * window_size)
            w = window_size
            h = window_size

            tiles.append([x, y, h, w])
    return np.array(tiles, dtype="uint32")

height = 3837
width = 5126
get_tiles(height, width)

输出:

array([[   0,    0, 1000, 1000],
       [1000,    0, 1000, 1000],
       [2000,    0, 1000, 1000],
       [3000,    0, 1000, 1000],
       [4000,    0, 1000, 1000],
       [   0, 1000, 1000, 1000],
       [1000, 1000, 1000, 1000],
       [2000, 1000, 1000, 1000],
       [3000, 1000, 1000, 1000],
       [4000, 1000, 1000, 1000],
       [   0, 2000, 1000, 1000],
       [1000, 2000, 1000, 1000],
       [2000, 2000, 1000, 1000],
       [3000, 2000, 1000, 1000],
       [4000, 2000, 1000, 1000]], dtype=uint32)

如您所见，我的 [x, y, h, w] 矩阵不正确，因为有一些 x,y 点位于 3837x5126 像素图像之外。

如有任何帮助，我们将不胜感激!

---

编辑:

这里是 answer @HansHirse gave添加了一些测试。

import unittest
import math
import numpy as np

def tile(h, w, tile_width=None, tile_height=None, window_size=100):
    np.seterr(divide='ignore', invalid='ignore')

    if not tile_width:
        tile_width = window_size

    if not tile_height:
        tile_height = window_size

    wTile = tile_width
    hTile = tile_height

    if tile_width > w or tile_height > h:
        raise ValueError("tile dimensions cannot be larger than origin dimensions")

    # Number of tiles
    nTilesX = np.uint8(np.ceil(w / wTile))
    nTilesY = np.uint8(np.ceil(h / hTile))

    # Total remainders
    remainderX = nTilesX * wTile - w
    remainderY = nTilesY * hTile - h

    # Set up remainders per tile
    remaindersX = np.ones((nTilesX-1, 1)) * np.uint16(np.floor(remainderX / (nTilesX-1)))
    remaindersY = np.ones((nTilesY-1, 1)) * np.uint16(np.floor(remainderY / (nTilesY-1)))
    remaindersX[0:np.remainder(remainderX, np.uint16(nTilesX-1))] += 1
    remaindersY[0:np.remainder(remainderY, np.uint16(nTilesY-1))] += 1

    # Initialize array of tile boxes
    tiles = np.zeros((nTilesX * nTilesY, 4), np.uint16)

    k = 0
    x = 0
    for i in range(nTilesX):
        y = 0
        for j in range(nTilesY):
            tiles[k, :] = (x, y, hTile, wTile)
            k += 1
            if j < (nTilesY-1):
                y = y + hTile - remaindersY[j]
        if i < (nTilesX-1):
            x = x + wTile - remaindersX[i]

    return tiles

class TestTilingWithoutRemainders(unittest.TestCase):
    def test_it_returns_tiles_without_overflow(self):
        self.assertEqual(tile(500, 500, window_size=500).tolist(), np.array([[0, 0, 500, 500]], dtype="uint16").tolist())
        self.assertEqual(tile(250, 500, window_size=250).tolist(), np.array(
            [[0, 0, 250, 250], [250, 0, 250, 250]], dtype="uint16"
            ).tolist())

        self.assertEqual(tile(500, 250, window_size=250).tolist(), np.array(
            [[0, 0, 250, 250], [0, 250, 250, 250]], dtype="uint16"
            ).tolist())

class TestTilingWithRemainders(unittest.TestCase):
    def test_it_returns_tiles_with_overflow(self):
        self.assertEqual(tile(500, 501, window_size=500).tolist(), np.array(
            [[0, 0, 500, 500], [1, 0, 500, 500]], dtype="uint16"
            ).tolist())


        self.assertEqual(tile(251, 250, window_size=250).tolist(), np.array(
            [[0, 0, 250, 250], [0, 1, 250, 250]], dtype="uint16"
            ).tolist())


class TestTilingWithInvalidWindowSizes(unittest.TestCase):
    def test_it_raises_an_error_with_invalid_tile_height(self):
        self.assertRaises(ValueError, tile, 500, 500, tile_height=50000000)

    def test_it_raises_an_error_with_invalid_tile_width(self):
        self.assertRaises(ValueError, tile, 500, 500, tile_width=50000000)

    def test_it_raises_an_error_with_invalid_window_size(self):
        self.assertRaises(ValueError, tile, 500, 500, window_size=50000000)

Answer 1

这是我的解决方案。不幸的是，我的代码不是基于您的代码，但我希望您仍然可以遵循它。主要方法与您在问题中描述的完全相同。

让我们看一下代码:

import cv2
import numpy as np

# Some image; get width and height
image = cv2.resize(cv2.imread('path/to/your/image.png'), (512, 383))
h, w = image.shape[:2]

# Tile parameters
wTile = 100
hTile = 100

# Number of tiles
nTilesX = np.uint8(np.ceil(w / wTile))
nTilesY = np.uint8(np.ceil(h / hTile))

# Total remainders
remainderX = nTilesX * wTile - w
remainderY = nTilesY * hTile - h

# Set up remainders per tile
remaindersX = np.ones((nTilesX-1, 1)) * np.uint16(np.floor(remainderX / (nTilesX-1)))
remaindersY = np.ones((nTilesY-1, 1)) * np.uint16(np.floor(remainderY / (nTilesY-1)))
remaindersX[0:np.remainder(remainderX, np.uint16(nTilesX-1))] += 1
remaindersY[0:np.remainder(remainderY, np.uint16(nTilesY-1))] += 1

# Initialize array of tile boxes
tiles = np.zeros((nTilesX * nTilesY, 4), np.uint16)

# Determine proper tile boxes
k = 0
x = 0
for i in range(nTilesX):
    y = 0
    for j in range(nTilesY):
        tiles[k, :] = (x, y, hTile, wTile)
        k += 1
        if (j < (nTilesY-1)):
            y = y + hTile - remaindersY[j]
    if (i < (nTilesX-1)):
        x = x + wTile - remaindersX[i]

print(tiles)

对于尺寸为 [512, 383] 且拼贴大小为 [100, 100] 的图像，tiles 数组如下所示:

[[  0   0 100 100]
 [  0  94 100 100]
 [  0 188 100 100]
 [  0 283 100 100]
 [ 82   0 100 100]
 [ 82  94 100 100]
 [ 82 188 100 100]
 [ 82 283 100 100]
 [164   0 100 100]
 [164  94 100 100]
 [164 188 100 100]
 [164 283 100 100]
 [246   0 100 100]
 [246  94 100 100]
 [246 188 100 100]
 [246 283 100 100]
 [329   0 100 100]
 [329  94 100 100]
 [329 188 100 100]
 [329 283 100 100]
 [412   0 100 100]
 [412  94 100 100]
 [412 188 100 100]
 [412 283 100 100]]

您将获得 24 个图 block ，每个图 block 的大小为 [100, 100]，并且尽可能有最相似的重叠。

如果我们切换到尺寸为 [500, 300] 的图像，我们会得到这些 tiles:

[[  0   0 100 100]
 [  0 100 100 100]
 [  0 200 100 100]
 [100   0 100 100]
 [100 100 100 100]
 [100 200 100 100]
 [200   0 100 100]
 [200 100 100 100]
 [200 200 100 100]
 [300   0 100 100]
 [300 100 100 100]
 [300 200 100 100]
 [400   0 100 100]
 [400 100 100 100]
 [400 200 100 100]]

如您所见，只剩下 15 个图 block ，并且完全没有重叠。

希望对您有所帮助!