.pbm文件图像渲染-[vhold] scanline-wiggles? [英] .pbm file image render - [vhold] scanline-wiggles?
问题描述
我正在尝试破解一个程序,以读取pbm,pgm或ppm文件,并使用 image
运算符将该图像渲染到Postscript输出设备中。只是测试 P4
输入(二进制可移植(1位)位图)路径,但我的输出却很麻烦。
I'm trying to hack-up a program to read a pbm, pgm, or ppm file and render the image to the postscript output device using the image
operator. Just testing the P4
input (binary portable (1-bit) bitmap) path, but my output is all screwy.
%!
% cf. http://en.wikipedia.org/wiki/Netpbm_format
% cf. http://en.wikipedia.org/wiki/Computer_Graphics (origin of image)
% $ wget http://upload.wikimedia.org/wikipedia/commons/thumb/2/23/Spacewar%21-PDP-1-20070512.jpg/320px-Spacewar%21-PDP-1-20070512.jpg
% $ convert 320px-Spacewar%21-PDP-1-20070512.jpg spacewar.pbm
% $ convert 320px-Spacewar%21-PDP-1-20070512.jpg spacewar.pgm
% $ convert 320px-Spacewar%21-PDP-1-20070512.jpg spacewar.ppm
/filename (spacewar.pbm) def
%/filename (spacewar.pgm) def
%/filename (spacewar.ppm) def
/infile filename (r) file def
/readscale false def
% Read magic number
infile token pop <<
/P1 { /depth 1 def
/readscale false def
/filetype /ascii def }
/P2 { /depth 8 def
/readscale true def
/filetype /ascii def }
/P3 { /depth 24 def
/readscale true def
/filetype /ascii def }
/P4 { /depth 1 def
/readscale false def
/filetype /binary def }
/P5 { /depth 8 def
/readscale true def
/filetype /binary def }
/P6 { /depth 24 def
/readscale true def
/filetype /binary def }
>> exch 2 copy known not{pop/default}if get exec
% Read header
/buf 256 string def
infile buf readline pop % line
(1:)print dup ==
(#) { % line (#)
(2a:)print 1 index =
search { % post (#) pre
pop pop pop %
infile buf readline pop % (#) next-line
(#) % next-line (#)
(2b pstack\n)print pstack()=
}{ % line
(2c:)print dup ==
exit
} ifelse
} loop % line
pstack()=
token pop /height exch def
token pop /width exch def
readscale {
token pop /scale exch def
}{
pop
}ifelse
/buf width
depth mul
8 div ceiling cvi
string def
(bufsize: )print buf length =
/pad
buf length 8 mul
width sub def
(pad: )print pad =
/readdata <<
/ascii { % file buf
0 1 width 1 sub { % file buf i
2 index token pop % file buf i
} for
}
/binary { % file buf
readstring pop
%dup length 0 ne { 0 1 index length pad sub getinterval } if
dup == flush
%(bin)= flush
}
>> filetype get def
%errordict/rangecheck{pstack dup length = quit}put
width
height
depth
[ 1 0 0 -1 0 height ]
{
infile buf readdata
} image
showpage
我很确定问题出在我对行的字节宽度和预期填充的计算:
I'm pretty sure the problem is my calculation of the byte-width of a row and the expected padding:
/buf width
depth mul
8 div ceiling cvi
string def
(bufsize: )print buf length =
/pad
buf length 8 mul
width sub def
(pad: )print pad =
但这似乎是正确的,当我逐步执行它时。对于这个215位宽的位图,每行可获得27个字节。
But that seems, right, when I step through it. For this 215-bit-wide bitmap, I get 27-bytes per row.
编辑:删除 pad -chop很有帮助。也许我需要添加额外填充?
Removing the "pad"-chop helps. Perhaps I need to add extra padding?
问题在输出中得到了证明:
The problem is demonstrated in the output:
在此答案的末尾可以找到类似但更简单的程序。
Where the similar, but simpler program from the end of this answer renders ok.
推荐答案
哦,亲爱的,这真是愚蠢。
Oh, dearie me, that was stupid.
我碰了两行:
55 token pop /width exch def
56 token pop /height exch def
在我键入的最后一次编辑期间所有这些都传给我:
It all came to me during that last edit where I typed:
对于这215位宽位图,我每行得到27个字节。
For this 215-bit-wide bitmap, I get 27-bytes per row.
然后我再次查看 identify
输出。当然,215是高度,而不是宽度。
And then I looked again at the identify
output. Sure enough, 215 is the height, not the width.
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