使用 Python 将 BMP 转换为灰度

Question

我正在尝试使用 python 将 BMP 图像转换为灰度图像。这是正确的问题。

编写一个程序来编辑一个图像文件，把它变成灰度。 将每个像素替换为具有相同灰度级的像素 蓝色、绿色和红色分量。灰度级由下式计算 添加 30% 的红色电平，59% 的绿色电平，以及 蓝色水平的 11%。 （色觉视锥细胞 人眼对红光、绿光和蓝光的敏感度不同。）

我已经进行了一些编码，但它实际上并没有变成灰度，而是或多或少地变成了奇怪颜色的混合物。有人可以更正我的代码并看看我做错了什么吗？这是我的代码

from io import SEEK_CUR
def main():
    filename = input("Please enter the file name: ")

    # Open as a binary file for reading and writing
    imgFile = open(filename, "rb+")

    # Extract the image information.
    fileSize = readInt(imgFile, 2)
    start = readInt(imgFile, 10)
    width = readInt(imgFile, 18)
    height = readInt(imgFile, 22)

    # Scan lines must occupy multiples of four bytes.
    scanlineSize = width * 3
    if scanlineSize % 4 == 0:
        padding = 0
    else :
        padding = 4 - scanlineSize % 4

    # Make sure this is a valid image.
    if fileSize != (start + (scanlineSize + padding) * height):
        exit("Not a 24-bit true color image file.")

    # Move to the first pixel in the image.
    imgFile.seek(start)# Process the individual pixels.
    for row in range(height): #For each scan line
        for col in range(width): #For each pixel in the line
            processPixel(imgFile)

        # Skip the padding at the end.
        imgFile.seek(padding, SEEK_CUR)

    imgFile.close()## Processes an individual pixel.#@param imgFile the binary file containing the BMP image#

def processPixel(imgFile): #Read the pixel as individual bytes.
    theBytes = imgFile.read(3)
    blue = theBytes[0]
    green = theBytes[1]
    red = theBytes[2]

    # Process the pixel.
    newBlue = 255 - blue
    newGreen = 255 - green
    newRed = 255 - red

    # Write the pixel.
    imgFile.seek(-3, SEEK_CUR)# Go back 3 bytes to the start of the pixel.
    imgFile.write(bytes([newBlue, newGreen, newRed]))## Gets an integer from a binary file.#@param imgFile the file#@ param offset the offset at which to read the integer#@


def readInt(imgFile, offset): #Move the file pointer to the given byte within the file.
    imgFile.seek(offset)

    # Read the 4 individual bytes and build an integer.
    theBytes = imgFile.read(4)
    result = 0
    base = 1
    for i in range(4):
        result = result + theBytes[i] * base
        base = base * 256

    return result# Start the program.
main()

Answer 1

看这里

imgFile.write(bytes([newBlue, newGreen, newRed]))

让我们看看bytes做了什么

In [1]: ?bytes
Type:        type
String form: <type 'str'>
Namespace:   Python builtin
Docstring:
str(object='') -> string

Return a nice string representation of the object.
If the argument is a string, the return value is the same object.

In [2]: bytes(10)
Out[2]: '10'

In [3]: bytes([10,9])
Out[3]: '[10, 9]'

如您所见，它似乎并没有按照您的想法行事。

您正在寻找 bytearray 类

In [4]: ?bytearray
Type:        type
String form: <type 'bytearray'>
Namespace:   Python builtin
Docstring:
bytearray(iterable_of_ints) -> bytearray.
bytearray(string, encoding[, errors]) -> bytearray.
bytearray(bytes_or_bytearray) -> mutable copy of bytes_or_bytearray.
bytearray(memory_view) -> bytearray.

Construct an mutable bytearray object from:
  - an iterable yielding integers in range(256)
  - a text string encoded using the specified encoding
  - a bytes or a bytearray object
  - any object implementing the buffer API.

bytearray(int) -> bytearray.

Construct a zero-initialized bytearray of the given length.

In [5]: bytearray([1,2,3])
Out[5]: bytearray(b'\x01\x02\x03')

Answer 2

In this area of your code:

def processPixel(imgFile): #Read the pixel as individual bytes.
    theBytes = imgFile.read(3)
    blue = theBytes[0]
    green = theBytes[1]
    red = theBytes[2]
#ADD THIS LINE OF CODE
    gray = int((0.2126*red)+(0.7152*green)+(0.0722*blue))
    # Process the pixel.
#CHANGE IT TO THE FOLLOWING COLORS BY SUBTRACTING THE "gray" from 255
    newBlue = 255 - gray
    newGreen = 255 - gray
    newRed = 255 - gray