从RGB三元组数组制作BGR颜色条

Question

我有一个简单的任务，即根据768个元素的硬编码数组绘制色阶，代表256个BGR像素值。这是我的尝试：

import cv2
import numpy as np

img = np.zeros((50,256,3), np.uint8)

colorspace = [255, 255, 255, 253, 253, 253, 251, 251, 251, 249, 249, 249, 247, 247, 247, 245, 245, 245, 243, 243, 243, 241, 241, 241, 239, 239, 239, 237, 237, 237, 235, 235, 235, 233, 233, 233, 231, 231, 231, 229, 229, 229, 227, 227, 227, 225, 225, 225, 223, 223, 223, 221, 221, 221, 219, 219, 219, 217, 217, 217, 215, 215, 215, 213, 213, 213, 211, 211, 211, 209, 209, 209, 207, 207, 207, 205, 205, 205, 203, 203, 203, 201, 201, 201, 199, 199, 199, 197, 197, 197, 195, 195, 195, 193, 193, 193, 191, 191, 191, 189, 189, 189, 187, 187, 187, 185, 185, 185, 183, 183, 183, 181, 181, 181, 179, 179, 179, 177, 177, 177, 175, 175, 175, 173, 173, 173, 171, 171, 171, 169, 169, 169, 167, 167, 167, 165, 165, 165, 163, 163, 163, 161, 161, 161, 159, 159, 159, 157, 157, 157, 155, 155, 155, 153, 153, 153, 151, 151, 151, 149, 149, 149, 147, 147, 147, 145, 145, 145, 143, 143, 143, 141, 141, 141, 139, 139, 139, 137, 137, 137, 135, 135, 135, 133, 133, 133, 131, 131, 131, 129, 129, 129, 126, 126, 126, 124, 124, 124, 122, 122, 122, 120, 120, 120, 118, 118, 118, 116, 116, 116, 114, 114, 114, 112, 112, 112, 110, 110, 110, 108, 108, 108, 106, 106, 106, 104, 104, 104, 102, 102, 102, 100, 100, 100, 98, 98, 98, 96, 96, 96, 94, 94, 94, 92, 92, 92, 90, 90, 90, 88, 88, 88, 86, 86, 86, 84, 84, 84, 82, 82, 82, 80, 80, 80, 78, 78, 78, 76, 76, 76, 74, 74, 74, 72, 72, 72, 70, 70, 70, 68, 68, 68, 66, 66, 66, 64, 64, 64, 62, 62, 62, 60, 60, 60, 58, 58, 58, 56, 56, 56, 54, 54, 54, 52, 52, 52, 50, 50, 50, 48, 48, 48, 46, 46, 46, 44, 44, 44, 42, 42, 42, 40, 40, 40, 38, 38, 38, 36, 36, 36, 34, 34, 34, 32, 32, 32, 30, 30, 30, 28, 28, 28, 26, 26, 26, 24, 24, 24, 22, 22, 22, 20, 20, 20, 18, 18, 18, 16, 16, 16, 14, 14, 14, 12, 12, 12, 10, 10, 10, 8, 8, 8, 6, 6, 6, 4, 4, 4, 2, 2, 2, 0, 0, 0, 0, 0, 9, 2, 0, 16, 4, 0, 24, 6, 0, 31, 8, 0, 38, 10, 0, 45, 12, 0, 53, 14, 0, 60, 17, 0, 67, 19, 0, 74, 21, 0, 82, 23, 0, 89, 25, 0, 96, 27, 0, 103, 29, 0, 111, 31, 0, 118, 36, 0, 120, 41, 0, 121, 46, 0, 122, 51, 0, 123, 56, 0, 124, 61, 0, 125, 66, 0, 126, 71, 0, 127, 76, 1, 128, 81, 1, 129, 86, 1, 130, 91, 1, 131, 96, 1, 132, 101, 1, 133, 106, 1, 134, 111, 1, 135, 116, 1, 136, 121, 1, 136, 125, 2, 137, 130, 2, 137, 135, 3, 137, 139, 3, 138, 144, 3, 138, 149, 4, 138, 153, 4, 139, 158, 5, 139, 163, 5, 139, 167, 5, 140, 172, 6, 140, 177, 6, 140, 181, 7, 141, 186, 7, 141, 189, 10, 137, 191, 13, 132, 194, 16, 127, 196, 19, 121, 198, 22, 116, 200, 25, 111, 203, 28, 106, 205, 31, 101, 207, 34, 95, 209, 37, 90, 212, 40, 85, 214, 43, 80, 216, 46, 75, 218, 49, 69, 221, 52, 64, 223, 55, 59, 224, 57, 49, 225, 60, 47, 226, 64, 44, 227, 67, 42, 228, 71, 39, 229, 74, 37, 230, 78, 34, 231, 81, 32, 231, 85, 29, 232, 88, 27, 233, 92, 24, 234, 95, 22, 235, 99, 19, 236, 102, 17, 237, 106, 14, 238, 109, 12, 239, 112, 12, 240, 116, 12, 240, 119, 12, 241, 123, 12, 241, 127, 12, 242, 130, 12, 242, 134, 12, 243, 138, 12, 243, 141, 13, 244, 145, 13, 244, 149, 13, 245, 152, 13, 245, 156, 13, 246, 160, 13, 246, 163, 13, 247, 167, 13, 247, 171, 13, 248, 175, 14, 248, 178, 15, 249, 182, 16, 249, 185, 18, 250, 189, 19, 250, 192, 20, 251, 196, 21, 251, 199, 22, 252, 203, 23, 252, 206, 24, 253, 210, 25, 253, 213, 27, 254, 217, 28, 254, 220, 29, 255, 224, 30, 255, 227, 39, 255, 229, 53, 255, 231, 67, 255, 233, 81, 255, 234, 95, 255, 236, 109, 255, 238, 123, 255, 240, 137, 255, 242, 151, 255, 244, 165, 255, 246, 179, 255, 248, 193, 255, 249, 207, 255, 251, 221, 255, 253, 235, 255, 255, 24]
color = [colorspace[i:i + 3] for i in xrange(0, len(colorspace), 3)]

for x in range(256):
    for (b,g,r) in color:
        cv2.line(img,(x,0),(x,49),(b,g,r), 1)

cv2.imwrite('ironblack.png', img)

输出应该是BGR值的渐变，而是我得到这个明亮的蓝色图像：

我在这里可以缺少什么？我怎么能做到这一点？

编辑：似乎所有线条都是使用colorspace列表中最后一项的颜色绘制的，即[255,255,24]（浅蓝色）。我不知道为什么会这样。我无法看到for循环的行为与此处的行为相似

Answer 1

我们并不需要绘制任何东西来实现这一目标。

我们从BGR三元组列表开始。我们可以把它变成一个numpy数组，reshape将它变为1行，256列和3个通道。

接下来，我们使用numpy.repeat根据需要多次重复此单行。这给了我们一个包含渐变的适当大小的BGR图像。

最后，如果输入颜色图是RGB而不是BGR（因为OpenCV imwrite需要BGR图像），我们可以使用cv2.cvtColor来切换蓝色和红色通道。

我们已经完成了 - 我们所需要的基本上是一个单行：

img = np.repeat(np.array(colorspace, np.uint8).reshape(1, 256, 3), 50, axis=0)

脚本：

import cv2
import numpy as np

colorspace = [255, 255, 255, 253, 253, 253, 251, 251, 251, 249, 249, 249, 247, 247, 247, 245, 245, 245, 243, 243, 243, 241, 241, 241, 239, 239, 239, 237, 237, 237, 235, 235, 235, 233, 233, 233, 231, 231, 231, 229, 229, 229, 227, 227, 227, 225, 225, 225, 223, 223, 223, 221, 221, 221, 219, 219, 219, 217, 217, 217, 215, 215, 215, 213, 213, 213, 211, 211, 211, 209, 209, 209, 207, 207, 207, 205, 205, 205, 203, 203, 203, 201, 201, 201, 199, 199, 199, 197, 197, 197, 195, 195, 195, 193, 193, 193, 191, 191, 191, 189, 189, 189, 187, 187, 187, 185, 185, 185, 183, 183, 183, 181, 181, 181, 179, 179, 179, 177, 177, 177, 175, 175, 175, 173, 173, 173, 171, 171, 171, 169, 169, 169, 167, 167, 167, 165, 165, 165, 163, 163, 163, 161, 161, 161, 159, 159, 159, 157, 157, 157, 155, 155, 155, 153, 153, 153, 151, 151, 151, 149, 149, 149, 147, 147, 147, 145, 145, 145, 143, 143, 143, 141, 141, 141, 139, 139, 139, 137, 137, 137, 135, 135, 135, 133, 133, 133, 131, 131, 131, 129, 129, 129, 126, 126, 126, 124, 124, 124, 122, 122, 122, 120, 120, 120, 118, 118, 118, 116, 116, 116, 114, 114, 114, 112, 112, 112, 110, 110, 110, 108, 108, 108, 106, 106, 106, 104, 104, 104, 102, 102, 102, 100, 100, 100, 98, 98, 98, 96, 96, 96, 94, 94, 94, 92, 92, 92, 90, 90, 90, 88, 88, 88, 86, 86, 86, 84, 84, 84, 82, 82, 82, 80, 80, 80, 78, 78, 78, 76, 76, 76, 74, 74, 74, 72, 72, 72, 70, 70, 70, 68, 68, 68, 66, 66, 66, 64, 64, 64, 62, 62, 62, 60, 60, 60, 58, 58, 58, 56, 56, 56, 54, 54, 54, 52, 52, 52, 50, 50, 50, 48, 48, 48, 46, 46, 46, 44, 44, 44, 42, 42, 42, 40, 40, 40, 38, 38, 38, 36, 36, 36, 34, 34, 34, 32, 32, 32, 30, 30, 30, 28, 28, 28, 26, 26, 26, 24, 24, 24, 22, 22, 22, 20, 20, 20, 18, 18, 18, 16, 16, 16, 14, 14, 14, 12, 12, 12, 10, 10, 10, 8, 8, 8, 6, 6, 6, 4, 4, 4, 2, 2, 2, 0, 0, 0, 0, 0, 9, 2, 0, 16, 4, 0, 24, 6, 0, 31, 8, 0, 38, 10, 0, 45, 12, 0, 53, 14, 0, 60, 17, 0, 67, 19, 0, 74, 21, 0, 82, 23, 0, 89, 25, 0, 96, 27, 0, 103, 29, 0, 111, 31, 0, 118, 36, 0, 120, 41, 0, 121, 46, 0, 122, 51, 0, 123, 56, 0, 124, 61, 0, 125, 66, 0, 126, 71, 0, 127, 76, 1, 128, 81, 1, 129, 86, 1, 130, 91, 1, 131, 96, 1, 132, 101, 1, 133, 106, 1, 134, 111, 1, 135, 116, 1, 136, 121, 1, 136, 125, 2, 137, 130, 2, 137, 135, 3, 137, 139, 3, 138, 144, 3, 138, 149, 4, 138, 153, 4, 139, 158, 5, 139, 163, 5, 139, 167, 5, 140, 172, 6, 140, 177, 6, 140, 181, 7, 141, 186, 7, 141, 189, 10, 137, 191, 13, 132, 194, 16, 127, 196, 19, 121, 198, 22, 116, 200, 25, 111, 203, 28, 106, 205, 31, 101, 207, 34, 95, 209, 37, 90, 212, 40, 85, 214, 43, 80, 216, 46, 75, 218, 49, 69, 221, 52, 64, 223, 55, 59, 224, 57, 49, 225, 60, 47, 226, 64, 44, 227, 67, 42, 228, 71, 39, 229, 74, 37, 230, 78, 34, 231, 81, 32, 231, 85, 29, 232, 88, 27, 233, 92, 24, 234, 95, 22, 235, 99, 19, 236, 102, 17, 237, 106, 14, 238, 109, 12, 239, 112, 12, 240, 116, 12, 240, 119, 12, 241, 123, 12, 241, 127, 12, 242, 130, 12, 242, 134, 12, 243, 138, 12, 243, 141, 13, 244, 145, 13, 244, 149, 13, 245, 152, 13, 245, 156, 13, 246, 160, 13, 246, 163, 13, 247, 167, 13, 247, 171, 13, 248, 175, 14, 248, 178, 15, 249, 182, 16, 249, 185, 18, 250, 189, 19, 250, 192, 20, 251, 196, 21, 251, 199, 22, 252, 203, 23, 252, 206, 24, 253, 210, 25, 253, 213, 27, 254, 217, 28, 254, 220, 29, 255, 224, 30, 255, 227, 39, 255, 229, 53, 255, 231, 67, 255, 233, 81, 255, 234, 95, 255, 236, 109, 255, 238, 123, 255, 240, 137, 255, 242, 151, 255, 244, 165, 255, 246, 179, 255, 248, 193, 255, 249, 207, 255, 251, 221, 255, 253, 235, 255, 255, 24]


def make_colorbar(colorspace, rows):
    assert len(colorspace) == 768
    color = np.array(colorspace, np.uint8)
    img_row = color.reshape(1, 256, 3)
    img = np.repeat(img_row, rows, axis=0)
    # If the input colormap was actually RGB...
    # img = cv2.cvtColor(img, cv2.COLOR_RGB2BGR)
    return img

cv2.imwrite('ironblack.png', make_colorbar(colorspace, 50))

生成的彩条图像：

或者如果输入实际上是RGB，那么：

Answer 2

这是通过对嵌套for循环和矩阵迭代的基本理解来解决的。想象一下，颜色空间数组（行）和图像宽度（列）形成2D矩阵。只需要获得对角线元素，即坐标相等的元素，而不是遍历每一行中的每一列。所以：

y=-1

for (r,g,b) in color:
    y = y + 1
    for x in range(256):
        if x == y:
            cv2.line(img,(x,0),(x,49),(b,g,r), 1)