使用PyPNG绘制一个简单的填充框

Question

我正在尝试使用python的png模块绘制一个简单的256x256像素的RGBA正方形。

我想使用png.Writer函数，我想我必须使用write()方法来提取它。然而，我没有任何运气！我对我当前的代码没有信心，所以我愿意从头开始接受建议

如果可能的话，我不喜欢使用PIL。

有什么建议吗？

Answer 1

我认为可能影响你的是格式，png似乎有三种格式……

>>> help(png)
    Boxed row flat pixel::

     list([R,G,B, R,G,B, R,G,B],
       [R,G,B, R,G,B, R,G,B])

    Flat row flat pixel::    

      [R,G,B, R,G,B, R,G,B,
       R,G,B, R,G,B, R,G,B]

    Boxed row boxed pixel::

      list([ (R,G,B), (R,G,B), (R,G,B) ],
           [ (R,G,B), (R,G,B), (R,G,B) ])

该alpha被附加到每个RGB序列的末尾。

 write(self, outfile, rows)
 |      Write a PNG image to the output file.  `rows` should be
 |      an iterable that yields each row in boxed row flat pixel format.
 |      The rows should be the rows of the original image, so there
 |      should be ``self.height`` rows of ``self.width * self.planes`` values.
 |      If `interlace` is specified (when creating the instance), then
 |      an interlaced PNG file will be written.  Supply the rows in the
 |      normal image order; the interlacing is carried out internally.

请注意each row in boxed row flat pixel format.

下面是一个绘制白色正方形的快速示例。

>>> rows = [[255 for element in xrange(4) for number_of_pixles in xrange(256)] for number_of_rows in xrange(256)]
>>> import numpy # Using numpy is much faster
>>> rows = numpy.zeros((256, 256 * 4), dtype = 'int')
>>> rows[:] = 255
>>> png_writer = png.Writer(width = 256, height = 256, alpha = 'RGBA')
>>> png_writer.write(open('white_panel.png', 'wb'), rows)

请注意，Writer还可以使用其他两种格式，这两种格式可能更容易使用。

     |  write_array(self, outfile, pixels)
     |      Write an array in flat row flat pixel format as a PNG file on
     |      the output file.  See also :meth:`write` method.
     |  
     |  write_packed(self, outfile, rows)
     |      Write PNG file to `outfile`.  The pixel data comes from `rows`
     |      which should be in boxed row packed format.  Each row should be
     |      a sequence of packed bytes.

尝试使用numpy在处理矩阵运算时要快得多，也容易得多，图像可以用矩阵来表示。

祝好运。

如果要打印颜色，则需要计算该颜色的RGB值，例如，红色是(255，0，0,255)。

import png
import numpy
rows = numpy.zeros((256, 256, 4), dtype = 'int') # eassier format to deal with each individual pixel
rows[:, :] = [255, 0, 0, 255] # Setting the color red for each pixel
rows[10:40, 10:40] = [0, 255, 255, 255] #  filled squared starting at (10,10) to (40,40)
locs = numpy.indices(rows.shape[0:2])
rows[(locs[0] - 80)**2 + (locs[1] - 80)**2 <= 20**2] = [255, 255, 0, 255] # yellow filled circle, with center at (80, 80) and radius 20
png_writer = png.Writer(width = 256, height = 256, alpha = 'RGBA') # create writer
png_writer.write(open('colors_panel.png', 'wb'), rows.reshape(rows.shape[0], rows.shape[1]*rows.shape[2])) # we have to reshape or flatten the most inner arrays so write can properly understand the format

Answer 2

下面是一个创建全红色png文件的简单示例：

import png

width = 255
height = 255
img = []
for y in range(height):
    row = ()
    for x in range(width):
        row = row + (255, 0, 0, 255)
    img.append(row)
with open('red.png', 'wb') as f:
    w = png.Writer(width, height, greyscale=False, alpha='RGBA')
    w.write(f, img)