MESSAGE
| DATE | 2016-11-15 |
| FROM | ruben safir
|
| SUBJECT | Subject: [Learn] Fwd: PNG coding
|
From learn-bounces-at-nylxs.com Tue Nov 15 18:12:11 2016
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From: ruben safir
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Subject: [Learn] Fwd: PNG coding
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hmmm
I simple struct would be a good starting point :(
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From: ruben safir
Newsgroups: comp.lang.c
Subject: PNG coding
Date: Tue, 15 Nov 2016 14:40:04 -0500
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Xref: panix comp.lang.c:1094867
Does anyone know of any sample code for reading PNG files that doesn't
include using libpng.... just straight direct access.
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From: ruben safir
Newsgroups: comp.lang.c
Subject: Re: PNG coding
Date: Tue, 15 Nov 2016 15:20:21 -0500
Organization: PANIX Public Access Internet and UNIX, NYC
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Xref: panix comp.lang.c:1094871
On 11/15/2016 03:02 PM, Rick C. Hodgin wrote:
> On Windows and with a C++ compiler, you can use the built-in
> Gdiplus::Bitmap object and load the png and then write it out
> as a standard .bmp format, which is much easier to access
> line-by-line
I can't use MS, and I'm not looking for a solution, just source code to
learn by, read and adapt.
FWIW, Rick, I wouldn't touch a slaveware MS OS if it was the last
platform on earth. I suggest strongly for you to try something else.
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Subject: Re: PNG coding
From: "Rick C. Hodgin"
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Xref: panix comp.lang.c:1094873
On Tuesday, November 15, 2016 at 3:20:29 PM UTC-5, ruben safir wrote:
> On 11/15/2016 03:02 PM, Rick C. Hodgin wrote:
> > On Windows and with a C++ compiler, you can use the built-in
> > Gdiplus::Bitmap object and load the png and then write it out
> > as a standard .bmp format, which is much easier to access
> > line-by-line
>
> I can't use MS, and I'm not looking for a solution, just source code to
> learn by, read and adapt.
>
> FWIW, Rick, I wouldn't touch a slaveware MS OS if it was the last
> platform on earth. I suggest strongly for you to try something else.
Couldn't agree more, though I also extend the definition to include
Mac OS and Linux among others:
http://www.libsf.org/wiki/index.php/Main_Page
https://github.com/RickCHodgin/libsf/tree/master/exodus
I named it Exodus in the 1990s, about six years before I became a
Christian. It was given that name because I wanted it to be "a mass
departure from evil" which was Microsoft.
Today I am pursuing Exodus an OS/2 compatible kernel with some more
modern extensions, called ES/2.
Best regards,
Rick C. Hodgin
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From: "James R. Kuyper"
Newsgroups: comp.lang.c
Subject: Re: PNG coding
Date: Tue, 15 Nov 2016 15:34:19 -0500
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Xref: panix comp.lang.c:1094875
On 11/15/2016 02:40 PM, ruben safir wrote:
> Does anyone know of any sample code for reading PNG files that doesn't
> include using libpng.... just straight direct access.
How about looking at libpng itself? It is the official reference
implementation for PNG, and the source code is available under a
permissive free software license. I'd think you'd learn at least as much
by looking at the code for the official reference implementation as
you'd learn by looking at any other code.
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From: Popping mad
Newsgroups: comp.lang.c
Subject: Re: PNG coding
Date: Tue, 15 Nov 2016 20:57:07 +0000 (UTC)
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Xref: panix comp.lang.c:1094877
On Tue, 15 Nov 2016 15:34:19 -0500, James R. Kuyper wrote:
> How about looking at libpng itself?
because after 15 years they suddenly broke half my images with their bug
update and I specifically need to work around it to fix my images, not
through it.
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From: "James R. Kuyper"
Newsgroups: comp.lang.c
Subject: Re: PNG coding
Date: Tue, 15 Nov 2016 16:12:15 -0500
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Xref: panix comp.lang.c:1094879
On 11/15/2016 03:57 PM, Popping mad wrote:
> On Tue, 15 Nov 2016 15:34:19 -0500, James R. Kuyper wrote:
>
>> How about looking at libpng itself?
>
> because after 15 years they suddenly broke half my images with their bug
> update and I specifically need to work around it to fix my images, not
> through it.
Reading the source code might be the easiest way to figure out how to
work around it.
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Subject: Re: PNG coding
From: jadill33-at-gmail.com
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Xref: panix comp.lang.c:1094892
On Tuesday, November 15, 2016 at 3:57:17 PM UTC-5, Popping mad wrote:
> On Tue, 15 Nov 2016 15:34:19 -0500, James R. Kuyper wrote:
>
> > How about looking at libpng itself?
>
> because after 15 years they suddenly broke half my images with their bug
> update and I specifically need to work around it to fix my images, not
> through it.
One option is to use a tool like Beyond Compare to compare the source trees
of the two versions of libpng to try to isolate the file change(s) that
caused your problem. If the versions are not too far apart (so that there
are not many large file differences), you may be able to merge the new file
versions from the new libpng into the old libpng and try to rebuild
incrementally to eliminate file changes that do not affect your images.
An alternative is that you can do the same in Subversion/git or other source
control program to visualize the differences. Commit the newest version of
libpng that works with your images to a repo, then copy over files from the
new version of libpng one at a time until you hack a version that works for
you.
You can also try contacting a libpng developer and if you have a couple
sample images that demonstrate the problem that you're able to share, they
may be considerate enough to do this analysis for you.
I've experienced something similar myself when I need to migrate Wireshark
plugin code to new major versions (e.g. 1.10->1.12->2.0->2.2) as the API
changes can be somewhat significant.
Best regards,
John D.
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From: Richard Heathfield
Newsgroups: comp.lang.c
Subject: Re: PNG coding
Date: Tue, 15 Nov 2016 21:45:21 +0000
Organization: Fix this later
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Xref: panix comp.lang.c:1094886
On 15/11/16 20:34, James R. Kuyper wrote:
> On 11/15/2016 02:40 PM, ruben safir wrote:
>> Does anyone know of any sample code for reading PNG files that doesn't
>> include using libpng.... just straight direct access.
>
> How about looking at libpng itself? It is the official reference
> implementation for PNG, and the source code is available under a
> permissive free software license. I'd think you'd learn at least as much
> by looking at the code for the official reference implementation as
> you'd learn by looking at any other code.
Just to encourage people to take James up on his suggestion, here are
some statistics from the libpng code.
Firstly, there'd better be LOTS of it. We want to learn a lot, don't we?
C files: 17
H files: 6
That looks promising, but not too impressive. Maybe we'd better count
lines instead:
Lines of C: 33593
Lines of H: 6791
Ah, that's better! But how much does it all *weigh*?
Kilobytes of C: 1116
Kilobytes of H: 304
Ah, that's very reassuring. Over a megabyte of C code. Let's remind
ourselves what we're doing: reading a PNG into memory, or writing it
out. Okay, a megabyte (of *source*) seems perfectly reasonable for that.
Now, we all know that there's nothing like the pre-processor for making
code readable, so let's hope they use the pre-processor a *lot*:
Number of lines of H starting #: 1667
Number of lines of C starting #: 2223
Yep, excellent.
Disappointingly, they supply a file, example.c, that shows you how to
use the library. You'd have thought you'd learn more from reading the
whole of the library code line by line in order to understand how to
call it.
But they redeem themselves in a most unexpected manner --- example.c
/does not compile/! And it's not supposed to. There's a comment to that
effect:
"This file does not currently compile, because it is missing certain
parts, like allocating memory to hold an image. You will have to supply
these parts to get it to compile."
They refer the interested reader, instead, to a 2000+ line test program,
which I presume was originally developed as an IOCCC entry. The main()
function calls a function named test_one_file(), which sounds quite a
promising place to start. Let's take a look at it:
/* Test one file */
static int
test_one_file(PNG_CONST char *inname, PNG_CONST char *outname)
{
static png_FILE_p fpin;
static png_FILE_p fpout; /* "static" prevents setjmp corruption */
pngtest_error_parameters error_parameters;
png_structp read_ptr;
png_infop read_info_ptr, end_info_ptr;
#ifdef PNG_WRITE_SUPPORTED
png_structp write_ptr;
png_infop write_info_ptr;
png_infop write_end_info_ptr;
#ifdef PNG_WRITE_FILTER_SUPPORTED
int interlace_preserved = 1;
#endif /* WRITE_FILTER */
#else /* !WRITE */
png_structp write_ptr = NULL;
Actually, since it's about 900 lines long, I don't think I'll show any
more of it. It's obviously all quite self-explanatory, and you won't
need any help at all in understanding it completely. Five minutes should
do it. Maybe ten if you're having a bad day. For the whole library?
Perhaps an hour. After all, it's only 40,000 lines.
--
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
Sig line 4 vacant - apply within
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From: "James R. Kuyper"
Newsgroups: comp.lang.c
Subject: Re: PNG coding
Date: Tue, 15 Nov 2016 17:15:55 -0500
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Xref: panix comp.lang.c:1094895
On 11/15/2016 04:45 PM, Richard Heathfield wrote:
> On 15/11/16 20:34, James R. Kuyper wrote:
>> On 11/15/2016 02:40 PM, ruben safir wrote:
>>> Does anyone know of any sample code for reading PNG files that doesn't
>>> include using libpng.... just straight direct access.
>>
>> How about looking at libpng itself? It is the official reference
>> implementation for PNG, and the source code is available under a
>> permissive free software license. I'd think you'd learn at least as much
>> by looking at the code for the official reference implementation as
>> you'd learn by looking at any other code.
>
> Just to encourage people to take James up on his suggestion, here are
> some statistics from the libpng code.
...
> Ah, that's very reassuring. Over a megabyte of C code. Let's remind
> ourselves what we're doing: reading a PNG into memory, or writing it
> out. Okay, a megabyte (of *source*) seems perfectly reasonable for that.
With you, it's sometimes hard to tell, but I'm going to assume you're
being sarcastic.
Keep in mind that this is the official reference implementation of PNG.
Any fully functional alternative to libpng is likely to be comparably
complicated - unless the implementors of libpng are exceptionally
incompetent. I know nothing about that personally, but it seems unlikely
that PNG would be as popular as it is if that were the case.
Would a less-than-fully-functional alternative be acceptable? In that
case, such an alternative could be a lot simpler - but that depends upon
which features of PNG ruben needs to handle correctly.
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From: Richard Heathfield
Newsgroups: comp.lang.c
Subject: Re: PNG coding
Date: Tue, 15 Nov 2016 22:41:23 +0000
Organization: Fix this later
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Xref: panix comp.lang.c:1094896
On 15/11/16 22:15, James R. Kuyper wrote:
> On 11/15/2016 04:45 PM, Richard Heathfield wrote:
>> On 15/11/16 20:34, James R. Kuyper wrote:
>>> On 11/15/2016 02:40 PM, ruben safir wrote:
>>>> Does anyone know of any sample code for reading PNG files that doesn't
>>>> include using libpng.... just straight direct access.
>>>
>>> How about looking at libpng itself? It is the official reference
>>> implementation for PNG, and the source code is available under a
>>> permissive free software license. I'd think you'd learn at least as much
>>> by looking at the code for the official reference implementation as
>>> you'd learn by looking at any other code.
>>
>> Just to encourage people to take James up on his suggestion, here are
>> some statistics from the libpng code.
> ...
>> Ah, that's very reassuring. Over a megabyte of C code. Let's remind
>> ourselves what we're doing: reading a PNG into memory, or writing it
>> out. Okay, a megabyte (of *source*) seems perfectly reasonable for that.
>
> With you, it's sometimes hard to tell,
Good. :-)
> but I'm going to assume you're being sarcastic.
On this occasion, you have correctly divined my intent.
> Keep in mind that this is the official reference implementation of PNG.
> Any fully functional alternative to libpng is likely to be comparably
> complicated - unless the implementors of libpng are exceptionally
> incompetent. I know nothing about that personally, but it seems unlikely
> that PNG would be as popular as it is if that were the case.
I don't think for a moment that they're incompetent. But readable code
clearly is not their priority.
>
> Would a less-than-fully-functional alternative be acceptable?
Hell yes!
> In that
> case, such an alternative could be a lot simpler - but that depends upon
> which features of PNG ruben needs to handle correctly.
I can't speak for Ruben's needs. But if anyone is planning to write a
simple PNG library, I would recommend the following interface:
/* returns width*height unsigned longs, encoding RGBA 00-FF */
unsigned long *png_load(const char *filename,
size_t *width,
size_t *height);
int png_save(const char filename,
unsigned long *frame,
size_t width,
size_t height);
And *nothing else*!
--
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
Sig line 4 vacant - apply within
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From: Melzzzzz
Newsgroups: comp.lang.c
Subject: Re: PNG coding
Date: Tue, 15 Nov 2016 23:49:03 +0100
Organization: albasani.net
Message-ID: <20161115234903.5851f221-at-maxa-pc>
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Xref: panix comp.lang.c:1094898
On Tue, 15 Nov 2016 22:41:23 +0000
Richard Heathfield wrote:
>
> I can't speak for Ruben's needs. But if anyone is planning to write a
> simple PNG library, I would recommend the following interface:
>
> /* returns width*height unsigned longs, encoding RGBA 00-FF */
> unsigned long *png_load(const char *filename,
> size_t *width,
> size_t *height);
>
> int png_save(const char filename,
> unsigned long *frame,
> size_t width,
> size_t height);
>
> And *nothing else*!
>
Well, one can write wrapper around libpng, possibly C++ ;)
--
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From: Melzzzzz
Newsgroups: comp.lang.c
Subject: Re: PNG coding
Date: Tue, 15 Nov 2016 23:42:14 +0100
Organization: albasani.net
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Xref: panix comp.lang.c:1094897
On Tue, 15 Nov 2016 17:15:55 -0500
"James R. Kuyper" wrote:
> On 11/15/2016 04:45 PM, Richard Heathfield wrote:
> > On 15/11/16 20:34, James R. Kuyper wrote: =20
> >> On 11/15/2016 02:40 PM, ruben safir wrote: =20
> >>> Does anyone know of any sample code for reading PNG files that
> >>> doesn't include using libpng.... just straight direct access. =20
> >>
> >> How about looking at libpng itself? It is the official reference
> >> implementation for PNG, and the source code is available under a
> >> permissive free software license. I'd think you'd learn at least
> >> as much by looking at the code for the official reference
> >> implementation as you'd learn by looking at any other code. =20
> >
> > Just to encourage people to take James up on his suggestion, here
> > are some statistics from the libpng code. =20
> ...
> > Ah, that's very reassuring. Over a megabyte of C code. Let's remind
> > ourselves what we're doing: reading a PNG into memory, or writing it
> > out. Okay, a megabyte (of *source*) seems perfectly reasonable for
> > that. =20
>=20
> With you, it's sometimes hard to tell, but I'm going to assume you're=20
> being sarcastic.
>=20
> Keep in mind that this is the official reference implementation of
> PNG. Any fully functional alternative to libpng is likely to be
> comparably complicated - unless the implementors of libpng are
> exceptionally incompetent. I know nothing about that personally, but
> it seems unlikely that PNG would be as popular as it is if that were
> the case.
>=20
> Would a less-than-fully-functional alternative be acceptable? In that=20
> case, such an alternative could be a lot simpler - but that depends
> upon which features of PNG ruben needs to handle correctly.
>=20
Well, how about Golang implementation?
[bmaxa-at-maxa-pc png]$ ls -l
total 28
drwxr-xr-x 3 bmaxa users 15 14.07.2015 20:01 testdata/
-rw-r--r-- 1 bmaxa users 3685 24.09.2016 02:52 example_test.go
-rw-r--r-- 1 bmaxa users 1768 11.12.2014 20:19 paeth.go
-rw-r--r-- 1 bmaxa users 2252 11.12.2014 20:19 paeth_test.go
-rw-r--r-- 1 bmaxa users 25588 28.10.2016 16:47 reader.go
-rw-r--r-- 1 bmaxa users 17597 28.10.2016 16:47 reader_test.go
-rw-r--r-- 1 bmaxa users 12530 01.10.2016 00:01 writer.go
-rw-r--r-- 1 bmaxa users 4670 11.12.2014 20:19 writer_test.go
reader/writer_test are bunch of golang routines to test every aspect of
library.
This is example decode:
func ExampleDecode() {
// This example uses png.Decode which can only decode PNG images.
// Consider using the general image.Decode as it can sniff and deco=
de any registered image format.
img, err :=3D png.Decode(gopherPNG())
if err !=3D nil {
log.Fatal(err)
}
levels :=3D []string{" ", "=E2=96=91", "=E2=96=92", "=E2=96=93", "=
=E2=96=88"}
for y :=3D img.Bounds().Min.Y; y < img.Bounds().Max.Y; y++ {
for x :=3D img.Bounds().Min.X; x < img.Bounds().Max.X; x++ {
c :=3D color.GrayModel.Convert(img.At(x, y)).(color=
.Gray)
level :=3D c.Y / 51 // 51 * 5 =3D 255
if level =3D=3D 5 {
level--
}
fmt.Print(levels[level])
}
fmt.Print("\n")
}
}
--=20
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