13 Mar
2013
13 Mar
'13
4:51 p.m.
Hi,
I am in the process of working on a new Amiga game, but I have the
graphics saved in .PNG format. I could convert them to the much
easier to decompress .IFF format, but .PNG image save many more
bytes (e.g image is 15KB saved as an .IFF vs. 9KB as a .PNG).
I have sucessfully decoded all the easy stuff, but am currently trying
to decode the IDAT chunk (where the image data is stored).
The format of the data is defined as follows (straight out of the RFC1951
Deflate Compression document available online):
??? 5 Bits: HLIT, # of Literal/Length codes - 257 (257 - 286)
??? 5 Bits: HDIST, # of Distance codes - 1 (1 - 32)
??? 4 Bits: HCLEN, # of Code Length codes - 4 (4 - 19)
??? (HCLEN + 4) x 3 bits: code lengths for the code length
??? alphabet given just above, in the order: 16, 17, 18,
??? 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
??? These code lengths are interpreted as 3-bit integers
??? (0-7); as above, a code length of 0 means the
??? corresponding symbol (literal/length or distance code
??? length) is not used.
??? HLIT + 257 code lengths for the literal/length alphabet,
??? encoded using the code length Huffman code
??? HDIST + 1 code lengths for the distance alphabet,
??? encoded using the code length Huffman code
??? The actual compressed data of the block,
??? encoded using the literal/length and distance Huffman
??? codes
??? The literal/length symbol 256 (end of data),
??? encoded using the literal/length Huffman code.
All the documents I found online either say use the zlib library or point to
the RFC1951 document :(
Does anyone know how to decode the literal / length (HLIT) and distance
codes (HDIST)?
Huffman compression was always something I found hard, but it seemed
much easier after finding this page online:
http://www.cs.duke.edu/csed/poop/huff/info/
Regards,
Andrew B
aliensrcooluk at yahoo.co.uk
13 Mar
13 Mar
7:25 p.m.
On 13/03/13 7:51 PM, Andrew Burton wrote:
Hi,
I am in the process of working on a new Amiga game, but I have the
graphics saved in .PNG format. I could convert them to the much
easier to decompress .IFF format, but .PNG image save many more
bytes (e.g image is 15KB saved as an .IFF vs. 9KB as a .PNG).
I have sucessfully decoded all the easy stuff, but am currently trying
to decode the IDAT chunk (where the image data is stored).
The format of the data is defined as follows (straight out of the RFC1951
Deflate Compression document available online):
5 Bits: HLIT, # of Literal/Length codes - 257 (257 - 286)
5 Bits: HDIST, # of Distance codes - 1 (1 - 32)
4 Bits: HCLEN, # of Code Length codes - 4 (4 - 19)
(HCLEN + 4) x 3 bits: code lengths for the code length
alphabet given just above, in the order: 16, 17, 18,
0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
These code lengths are interpreted as 3-bit integers
(0-7); as above, a code length of 0 means the
corresponding symbol (literal/length or distance code
length) is not used.
HLIT + 257 code lengths for the literal/length alphabet,
encoded using the code length Huffman code
HDIST + 1 code lengths for the distance alphabet,
encoded using the code length Huffman code
The actual compressed data of the block,
encoded using the literal/length and distance Huffman
codes
The literal/length symbol 256 (end of data),
encoded using the literal/length Huffman code.
All the documents I found online either say use the zlib library or point to
the RFC1951 document :(
Does anyone know how to decode the literal / length (HLIT) and distance
codes (HDIST)?
Huffman compression was always something I found hard, but it seemed
much easier after finding this page online:
http://www.cs.duke.edu/csed/poop/huff/info/
There is a very good library for working with PNG: libpng.
http://www.libpng.org/pub/png/libpng.html
Most likely the answer is in its source code. It would save you a lot of
time just to use that library, too.
--Toby
Regards,
Andrew B
aliensrcooluk at yahoo.co.uk
15 Mar
15 Mar
2:10 p.m.
On Mar 13, 2013, at 10:25 PM, Toby Thain <toby at telegraphics.com.au> wrote:
There is a very good library for working with PNG:
libpng.
http://www.libpng.org/pub/png/libpng.html
Most likely the answer is in its source code. It would save you a lot of time just to use
that library, too.
Source, yes. It's probably not a terrible candidate for using
wholesale on Amiga (both it and zlib, which it uses for
compression/decompression, are fairly lightweight), but for
specific purposes, a custom implementation may be faster and/or
smaller.
- Dave
13 Mar
13 Mar
7:36 p.m.
On 3/13/2013 7:51 PM, Andrew Burton wrote:
Hi,
I am in the process of working on a new Amiga game, but I have the
graphics saved in .PNG format. I could convert them to the much
easier to decompress .IFF format, but .PNG image save many more
bytes (e.g image is 15KB saved as an .IFF vs. 9KB as a .PNG).
Sorry I can't help you with the PNG decompression, but I think it is
very cool that you are working on a new Amiga game! Do you have a
website for the work-in-progress details?
Cheers,
Bryan
5 Sep
5 Sep
2:38 p.m.
----- Original Message -----
From: "Bryan Pope" <pet4032 at gmail.com>
To: <cctalk at classiccmp.org>
Sent: Thursday, March 14, 2013 3:36 AM
Subject: Re: PNG image decompression
Sorry I can't help you with the PNG decompression,
but I think it is
very cool that you are working on a new Amiga game! Do you have a
website for the work-in-progress details?
Cheers,
Bryan
Apologies for the slow reply...
I have just finished (as of Tuesday 3rd Sept) the ASM code to decode 16
colour images produced by Personal Paint (Amiga). I have started adding code
to decode 16 colour images from MS Paint - which shouldn't take long as all
the hard work decoding the IDAT data has already been done :)
Here's a link to a page where all the latest info regarding my game will be
displayed.
http://www.aliensrcooluk.com/mysite/glists/my_amigagames2
You can find a list of new Amiga games on the English Amiga Board too:
http://eab.abime.net/amiga-scene/68891-amiga-games-wip-released-index.html
Mine isn't listed their yet. Once it is playable I shall ask them to add it
to the list :)
Regards,
Andrew B
aliensrcooluk at yahoo.co.uk
15 Mar
15 Mar
1:28 p.m.
On Wed, 13 Mar 2013, Andrew Burton wrote:
Hi,
I am in the process of working on a new Amiga game, but I have the
graphics saved in .PNG format. I could convert them to the much
easier to decompress .IFF format, but .PNG image save many more
bytes (e.g image is 15KB saved as an .IFF vs. 9KB as a .PNG).
I have sucessfully decoded all the easy stuff, but am currently trying
to decode the IDAT chunk (where the image data is stored).
The format of the data is defined as follows (straight out of the RFC1951
Deflate Compression document available online):
If you support amigaos 3.x and newer, you can just use the
datatype.library, it will open any format you have the datatypes installed
for and give you an object to work with.
If you are aiming for older versions of amigaos, there are libpng on
aminet http://aminet.net/search?query=libpng .
regards
--
Jacob Dahl Pind | telefisk.org | fidonet 2:230/38.8
16 Mar
16 Mar
4:35 p.m.
From: "rachael at telefisk.org" <rachael at telefisk.org>
To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
Sent: Friday, 15 March 2013, 20:28
Subject: Re: PNG image decompression
On Wed, 13 Mar 2013, Andrew Burton wrote:
libpng and zlib are two choices. Personal Paint (by Cloanto in 1996)
also supports PNG's, though looking at their custom PNG library
(and even disassembling it) hasn't revealed anything terribly useful to
me. I'm sure some better coders could probably work out what it does.
I found a site (link below) where someone else had the same problem
and Mark Adler (one of the guys behind the PNG format and/or the
libraries) was kind enough to post some information. It has helped
me progress a little further :)
http://newsgroups.derkeiler.com/Archive/Comp/comp.compression/2009-04/msg00…
Thanks to everyone for your suggestions.
Regards,
Andrew B
aliensrcooluk at yahoo.co.uk
Hi,
I am in the process of working on a new Amiga game, but I have the
graphics saved in .PNG format. I could convert them to the much
easier to decompress .IFF format, but .PNG image save many more
bytes (e.g image is 15KB saved as an .IFF vs. 9KB as a .PNG).
I have sucessfully decoded all the easy stuff, but am currently trying
to decode the IDAT chunk (where the image data is stored).
The format of the data is defined as follows (straight out of the RFC1951
Deflate Compression document available online):
If you support amigaos 3.x and newer, you can just use the
datatype.library, it will open any format you have the datatypes installed
for and give you an object to work with.
If you are aiming for older versions of amigaos, there are libpng on
aminet http://aminet.net/search?query=libpng .
regards
--
Jacob Dahl Pind | telefisk.org | fidonet 2:230/38.8
15 Mar
15 Mar
3:09 p.m.
In article <1363218663.27571.YahooMailNeo at web171605.mail.ir2.yahoo.com>,
Andrew Burton <aliensrcooluk at yahoo.co.uk> writes:
I have sucessfully decoded all the easy stuff, but am
currently trying
to decode the IDAT chunk (where the image data is stored).
Why aren't you using libpng?
--
"The Direct3D Graphics Pipeline" free book
<http://tinyurl.com/d3d-pipeline>
The Computer Graphics Museum <http://computergraphicsmuseum.org>
The Terminals Wiki <http://terminals.classiccmp.org>
Legalize Adulthood! (my blog) <http://legalizeadulthood.wordpress.com>
16 Mar
16 Mar
4:24 p.m.
From: Richard <legalize at xmission.com>
To: cctalk <cctalk at classiccmp.org>
Sent: Friday, 15 March 2013, 22:09
Subject: Re: PNG image decompression
In article <1363218663.27571.YahooMailNeo at
web171605.mail.ir2.yahoo.com>,
? ? Andrew Burton <aliensrcooluk at yahoo.co.uk> writes:
Because that is far too easy and I wanted to learn how to decode the
PNG file format. Using a library teaches me nothing, not to mention
adds unecessary bulk (the routines I don't use) to whatever I'm using
PNG's in.
I have sucessfully decoded all the easy stuff,
but am currently trying
to decode the IDAT chunk (where the image data is stored).
Why aren't you using libpng?
6:34 p.m.
In article <1363476251.91693.YahooMailNeo at web171605.mail.ir2.yahoo.com>,
Andrew Burton <aliensrcooluk at yahoo.co.uk> writes:
From: Richard <legalize at xmission.com>
Meh. There's more important things to learn that aren't available in
canned libraries, IMO. Good game design and gameplay, for instance.
Why aren't you using libpng?
Because that is far too easy and I wanted to learn how to decode the
PNG file format. Using a library teaches me nothing, not to mention
adds unecessary bulk (the routines I don't use) to whatever I'm using
PNG's in.
Whatever you don't use doesn't get linked into your executable because
each "feature" in libpng is it's own compilation unit, IIRC.
--
"The Direct3D Graphics Pipeline" free book
<http://tinyurl.com/d3d-pipeline>
The Computer Graphics Museum <http://computergraphicsmuseum.org>
The Terminals Wiki <http://terminals.classiccmp.org>
Legalize Adulthood! (my blog) <http://legalizeadulthood.wordpress.com>
7:44 p.m.
On Sat, Mar 16, 2013 at 07:34:46PM -0600, Richard wrote:
Andrew Burton <aliensrcooluk at yahoo.co.uk>
writes:
Sometimes programming is an end in itself! And anyway, often shoe-horning
code that's lying around is a bigger battle than just writing your own that's
an exact fit.
John Wilson
D Bit
Because that is far too easy and I wanted to
learn how to decode the
PNG file format.
Meh. There's more important things to learn that aren't available in
canned libraries, IMO. Good game design and gameplay, for instance.
8:43 p.m.
In article <20130317024443.GA20737 at dbit.dbit.com>,
John Wilson <wilson at dbit.com> writes:
On Sat, Mar 16, 2013 at 07:34:46PM -0600, Richard
wrote:
I'm not saying that doing things on your own isn't a learning
experience.
However, if your goal is to build a fun game on the Amiga, there's
better ways to spend your time than going through every nook and
cranny of PNG. It's not even directly related to gameplay, only asset
loading.
--
"The Direct3D Graphics Pipeline" free book
<http://tinyurl.com/d3d-pipeline>
The Computer Graphics Museum <http://computergraphicsmuseum.org>
The Terminals Wiki <http://terminals.classiccmp.org>
Legalize Adulthood! (my blog) <http://legalizeadulthood.wordpress.com>
Andrew Burton <aliensrcooluk at
yahoo.co.uk> writes:
Sometimes programming is an end in itself! Because that is far too easy and I wanted to
learn how to decode the
PNG file format.
Meh. There's more important things to learn that aren't available in
canned libraries, IMO. Good game design and gameplay, for instance.
3892
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4068
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11 comments
7 participants
participants (7)
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aliensrcooluk＠yahoo.co.uk -
fraveydank＠gmail.com -
legalize＠xmission.com -
pet4032＠gmail.com -
rachael＠telefisk.org -
toby＠telegraphics.com.au -
wilson＠dbit.com