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tscheingeld
Asked: 2024-10-22 01:15:32 +0800 CST

在 PNG 文件中绘制矩形

  • 772

TLDR：我的目标很简单。我有一个 PNG 文件。我想使用 Python 在其中绘制一个矩形并将其保存到新文件中。

我有一个 PNG 文件（附在本帖中）。我只想使用 Python 在图像中绘制一个矩形，然后将图像保存到新文件中。以下代码不起作用：

import png

org_path = './arragon.png'
altered_path = './altered.png'

f = open(org_path, 'rb')
image = png.Reader(file=f)
width, height, rows, metadata = image.read()

for row in rows:
    for i in range(len(row)):
        row[i] = 255

writer = png.Writer(
    width=width,
    height=height,
    bitdepth=metadata['bitdepth'],
    greyscale=metadata['greyscale'],
    alpha=metadata['alpha']
)

writer.write(open(altered_path, 'wb'), rows)

最后一行产生以下错误：

Traceback (most recent call last):
File "/home/miko/tmp/alter-image/./edit.py", line 23, in <module>
    writer.write(open(altered_path, 'wb'), rows)
File "/home/miko/.local/lib/python3.10/site-packages/png.py", line 670, in write
    raise ProtocolError(
png.ProtocolError: ProtocolError: rows supplied (0) does not match height (450)

现在，为了分解它，我尝试将图像对象复制到 Writer，而不进行任何更改：

import png

f = open(org_path, 'rb')
image = png.Reader(file=f)
width, height, rows, metadata = image.read()

writer = png.Writer(
    width=width,
    height=height,
    bitdepth=metadata['bitdepth'],
    greyscale=metadata['greyscale'],
    alpha=metadata['alpha']
)

writer.write(open(altered_path, 'wb'), rows)

然后我收到此消息：

Traceback (most recent call last):
File "/home/miko/tmp/alter-image/./edit.py", line 23, in <module>
    writer.write(open(altered_path, 'wb'), rows)
File "/home/miko/.local/lib/python3.10/site-packages/png.py", line 668, in write
    nrows = self.write_passes(outfile, check_rows(rows))
File "/home/miko/.local/lib/python3.10/site-packages/png.py", line 703, in write_passes
    return self.write_packed(outfile, rows)
File "/home/miko/.local/lib/python3.10/site-packages/png.py", line 738, in write_packed
    for i, row in enumerate(rows):
File "/home/miko/.local/lib/python3.10/site-packages/png.py", line 658, in check_rows
    raise ProtocolError(
png.ProtocolError: ProtocolError: Expected 633 values but got 211 values, in row 0

我完全搞不清楚哪里出了问题。有人能告诉我该怎么做吗？

阿拉贡

python

2 个回答

  1. Best Answer

    您正在读取一个每像素 8 位的调色板图像。Writer除非您为其指定参数，否则对象不会使用该格式palette。它试图写入每像素 24 位，因此一行远远不够。

    做出以下细微的改变：

    writer = png.Writer(
    width=width,
    height=height,
    bitdepth=metadata['bitdepth'],
    greyscale=metadata['greyscale'],
    alpha=metadata['alpha'],
    palette=metadata['palette']
)
    • 0

  2. 我搞明白了。它有点笨拙，因为它会改变调色板中一种颜色的值。但是，它确实绘制了一个矩形，而这正是我真正需要的。

    import png

org_path = './arragon.png'
altered_path = './altered.png'

f = open(org_path, 'rb')
image = png.Reader(file=f)
width, height, rows, metadata = image.read()
palette = metadata['palette']

rows = list(rows)

for r in range(len(rows)):
    rows[r] = list(rows[r])

palette[0] = (255, 0, 0)

for r in range(20, 150):
    row = rows[r]

    for i in range(20, 100):
        row[i] = 0

writer = png.Writer(
    width=width,
    height=height,
    bitdepth=metadata['bitdepth'],
    greyscale=metadata['greyscale'],
    alpha=metadata['alpha'],
    palette=metadata['palette']
)

writer.write(open(altered_path, 'wb'), rows)
    • 0

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