Numpy和16位PGM [英] Numpy and 16-bit PGM

问题描述

使用numpy在Python中读取16位PGM图像的有效而清晰的方法是什么?

What is an efficient and clear way to read 16-bit PGM images in Python with numpy?

由于PIL错误，我无法使用PIL加载16位PGM图像 .我可以使用以下代码读取标题:

I cannot use PIL to load 16-bit PGM images due to a PIL bug. I can read in the header with the following code:

dt = np.dtype([('type', 'a2'),
               ('space_0', 'a1', ),
               ('x', 'a3', ),
               ('space_1', 'a1', ),
               ('y', 'a3', ),
               ('space_2', 'a1', ),
               ('maxval', 'a5')])
header = np.fromfile( 'img.pgm', dtype=dt )
print header

这将打印正确的数据:('P5', ' ', '640', ' ', '480', ' ', '65535')但是我感觉这并不是最好的方法.除此之外，我不知道如何找出如何用偏移量为size(header)的16位以y(在本例中为640x480)读取x的以下数据.

This prints the correct data: ('P5', ' ', '640', ' ', '480', ' ', '65535') But I have a feeling that is not quite the best way. And beyond that, I'm having trouble how to figure out how to read in the following data of x by y (in this case 640x480) by 16-bit with the offset of size(header).

添加了图像

读取和显示图像的MATLAB代码为:

MATLAB code to read and display the image is:

I = imread('foo.pgm'); 
imagesc(I);

看起来像这样:

推荐答案

import re
import numpy

def read_pgm(filename, byteorder='>'):
    """Return image data from a raw PGM file as numpy array.

    Format specification: http://netpbm.sourceforge.net/doc/pgm.html

    """
    with open(filename, 'rb') as f:
        buffer = f.read()
    try:
        header, width, height, maxval = re.search(
            b"(^P5\s(?:\s*#.*[\r\n])*"
            b"(\d+)\s(?:\s*#.*[\r\n])*"
            b"(\d+)\s(?:\s*#.*[\r\n])*"
            b"(\d+)\s(?:\s*#.*[\r\n]\s)*)", buffer).groups()
    except AttributeError:
        raise ValueError("Not a raw PGM file: '%s'" % filename)
    return numpy.frombuffer(buffer,
                            dtype='u1' if int(maxval) < 256 else byteorder+'u2',
                            count=int(width)*int(height),
                            offset=len(header)
                            ).reshape((int(height), int(width)))


if __name__ == "__main__":
    from matplotlib import pyplot
    image = read_pgm("foo.pgm", byteorder='<')
    pyplot.imshow(image, pyplot.cm.gray)
    pyplot.show()

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