PNG compression levels
I need to save some files a PNG. Never having used PNG
before, I'm a bit unsure about the meaning of compression
Is it true that PNG is completely lossless regardless of the
compression level, and that compression level only determines
how fast or slow a file will be to save and open? Is that
the only consideration for PNG compression levels?
Joe <firstname.lastname@example.org> wrote:
> I need to save some files a PNG. Never having used PNG
> before, I'm a bit unsure about the meaning of compression
I would like to compress some Oracle tables to see how well they can
compress. Is there some sort of a guide or rules for how well tables
can compress based on their datatypes? I know that some of our DBA's
have managed to compress tables up to 70%.
What tables if any shouldn't be compressed? Are there datatypes that
compresses better or is it block related only?
I would like to understand and decide which tables should be compressed
without testing each table.
> I would like to compress some Oracle tables to see how...compression level in SSH2
How can one set compression level different than 6 in SSH2?
If it's impossible, why was it possible in SSH1?
There are big differences when I compared:
1) compression level 9 in SSH1,
2) compression level 6 in SSH2,
over a slow link, with huge amounts of text.
...ZLIB Compression levels
I am using zlib 1.1.4 for Solaris and would like to know the
Is there a "C" api call that I can make on a compressed file that will
return me the compression level used to compress that file. If not,
can you provide me with a piece of code that can accomplish this task.
It would be very much appreciated.
Secondly, can you provide me with a list of compression levels. The
only ones I am aware of are below. Are these accurate?
email@example.com (Stu)...JPEG compression and quality level
Is there a way or some (free) 3rd party algorithm to determine the JPEG
compression level? We need to make sure that some JPEGs have a certain
quality. Images under a some threshold value shall be rejected form
E.g. our JPEG quality scale would be from 0-100%, then all images below
70% can't be submitted. (100% is the lowest compression possible, large
Is there such an algorithm?
Karsten Wutzke <firstname.lastname@example.org> writes:
> Is there a way or some (free) 3rd party algorithm to determine the
> JPEG compression level...4-level image compression ?
I'm playing with a small system where the display is 320x240 pixels,
with 4 grey levels. So a picture takes about 19200 bytes.
Now I'm quite sure that these images can be reduced in size
but the algorithms I'm aware of deal with 2-level only (fax) or many-level
images (GIF/PNG etc.). Furthermore, my CPU power and RAM are quite reduced
so even a sub-optimal algorithm could do the trick, as long as it saves
some storage space. The final decoder will be hand-coded in asm
and developed in C.
currently, my idea is to use a paeth predictor followed
by a static huffman encoded en...OT unbelieveable PNG compression
Here is a picture that contains full RGB colours 256x256x256. Each pixel is
represented by different colour and the picture containr full 16.8M colours.
The picture has resolution 4096x4096 pixels and the colours in the picture
are placed in the way to propose maximal possible compression in PNG format.
The size of this compressed picture is just 58kB.
source : http://www.dsl.sk/article.php?article=2850&title=
Bohus Kr�l wrote:
> Here is a picture that contains full RGB colours 256x256x256. Each pixel
> is represented by di...Compressing compressed files?
I have a really crazy idea:
Supposing you took a compressed file (any format) and pass it to a
bijective decompressor,In principle the data should become less
random. After that you can recompress the data with a superior
My reasoning is as follows:
The set of input data for most general purpose compression algorithms
tends to overlap. Within a certain margin , the set of compressed
files overlaps too.
I tried this out on a couple of files with David Scott's BICOM but I
didn't get any positive result.
My idea was that since PPMII does 40 - 50 % better than ZIP and there
...compressing compressed video
Is it possible to noticeably compress already compressed video (DivX/MPEG)
even futher using a loseless compression program? Which programs offer the
highest compression radios in this case?
> Is it possible to noticeably compress already compressed video (DivX/MPEG)
> even futher using a loseless compression program?
Yes, but not by much if at all. The most lossless compression I have
seen of an .AVI occured because the PCM audio was uncompressed. The
only .AVIs you'll see major compression occur is when there is so much
redundant information in a frame or ...compress utility != Compress::Zlib::compress() on linux and Windows
For some reason when the compress utility is used to
create a .Z file, the result is not recognized by the Compress::Zlib
uncompress() function (on either Linux
And it turns out that Compress::Zlib::compress() produces
a _different_ .Z file. Editing the two seems to show that
the contents are the same after a certain point and thus
the headers differ. DOH!
I am running with perl v5.8.6, in which Compress::Zlib
v1.33 is bundled. (v1.34 was released in 2005-01; but I
doubt if 1.33 is drastically out of date.)
Can anyone shed some light on this? If so, you'll be doing
better ...To Compress or Not To Compress -- That is the Question !
I'm running a website (I have three sites on my older Dell -- Pentium 4
with 2GB of Memory and a 350Gig Harddrive) with an xHarbour .exe as the CGI
If I have many simultaneous clients, is there a significant benefit or
penalty to compressing the .exe ?
Currently, one of the compressed executables is 486,400 bytes.
Uncompressed, it is 1,076,224 bytes.
I welcome your opinions.
In case of your setup IMHO the compressed .exe has no advantages, the
decompressing operation ( aka UnZip )
- eats the serv...Compression in PS level 2
I want to compress image data in PS using language level 2.
How to use runlength and other filters to get this done.....
"Needo" <email@example.com> wrote:
>I want to compress image data in PS using language level 2.
>How to use runlength and other filters to get this done.....
The PostScript Language Reference has the details, and either defines
the compressed data format, or gives a refererence to where it is
Some filters are very simple to compress for (RunLength), for some you
would use outside code (e.g. zlib for FlateDecode), and for others
i...Level 0 compression in ZipArchive
Is there a way to use php's ZipArchive and specify No Compression?
Something similar to "zip -0" on the command line. Thanks very much.
...compression level with tarfile (w:gz) ?
I was wondering if it possible to specify a compression level when I
tar/gzip a file in Python using the tarfile module. I would like to
specify the highest (9) compression level for gzip.
t = tarfile.open(tar_file_name+'.tar.gz', mode='w:gz:9')
When I create a simple tar and then gzip it 'manually' with compression
level 9, I get a smaller archive than when I have this code execute with
the w:gz option.
Is the only way to accomplish the higher rate to create a tar file
and then use a different module to gzip it (assuming I can specify
the compr...Low Level Data Compression, Language Impact?
es a method of data compression. The exact impact on source code structure =
and hardware architecture are not yet fully known. I'd assume people in thi=
s group know assembly level and below as well as more high level ideas.
...J2k Lossy Compression
I am using jpeg 2000 lossy compression on my dicom images. I have
noticed that often the default values in the header for window level
are no longer appropriate after the image is compressed. Are window
center and window width generally updated when j2k lossy compression
is applied? Also, should I be updating the smallest/largest pixel
value ( 0028,0106 and 0028,0107 ) after compression?
Thanks in advance for any answers.
as DICOM Lossy Compression usually requires the generation of a new
Instance, you should appropriately all presentation rel...colour bits compress? (png 48 bits)
I know that lower bits will be cut when the "system bits"
does not corresponds to the "image bits".
For example, if I create 48-bit PNG image, and present it
with 30-bit dispay system, how precisely the original RGB
information can remained (on the displayed image)?
I would like to know how it happens more qunatitatively.
Does it depends on the display system?
Would it be possible to let me have some imformation, say
is there any documentations I could find?
Thank you very much for your help in advance.
...Optimum number of steps for PNG compression (Infranview): about 8.
Optimum number of steps for PNG compression (Infranview): about 8.
The PNG compression plug-in seems to have a logrythmic decrease in image
size, step by step.
File : 'changes.txt' - Info about IrfanView updates (important changes
Author: Irfan Skiljan
WWW : http://www.irfanview.com
Version 3.97 (Release date: 2005-04-22)
- New "Browse Subfolders" dialog, when folder end/begin re...How to recompress existing zip files with a higher level of compression
I have loads (1000+) zip files, that were compressed with the default
level of compression. Is there any easy way of recompressing these
files, with a higher level of compression??
I don't want to compress the existing zip file into another zip file,
but rather recompress the contents of the file.
> I have loads (1000+) zip files, that were compressed with the default
> level of compression. Is there any easy way of recompressing these
> files, with a higher level of compression??
> I don't want to compress the existing zip file int...c is a low-level language or neither low level nor high level language
I have a doubt that 'c' is low level language or neither low level
nor high level language.please give me details.
In article <firstname.lastname@example.org>,
pabbu <email@example.com> wrote:
> I have a doubt that 'c' is low level language or neither low level
>nor high level language.please give me details.
Rather than have this turn into a long quibble about semantics,
let me turn the question around and ask you:
What do *you* mean by "low level language"?
What do *you* mean by "h...Level 14 Privilege Level
I want to create a username/password with a privilege level of
14. Creating it is easy enough. It just takes the syntax of
'username cisco privilege 14 password cisco'.
The issue is that I want level 14 to be able to do [almost]
anything that the level 15 password can do *except*
add/remove/delete/change passwords. At some future point, I might
want to restrict some other commands but which other ones are yet to
I'm not really sure how to go about doing that. Does anyone
have any feedback on this? Syntax for the commands would be great if
you k...Compress an already compressed Jpeg
We are trialing some software that very basically allows your average Joe
with the correct client software installed send an image file via the
internet to a server running the server side of this software. While this is
already very easy to do with a bit of HTML code and asp/php e.t.c to receive
and manipulate the file. This software claims to compress the image before
it is sent and then decompress the server end with no loss using file
compression rather than further image compression. What's more it claims it
compresses them up to 80% compression before transfer!
While I can believe t...Building Voxel arrays from png files (compression, analysis, and visualization)
I have no previous programming experience, prior to this I was a
biology student with some computing background. I am working on
speeding up the below script and trying to reduce the amount of data
lost during compression. Currently I am relying on the IDL
Interpolation to create a new voxel array from a series of
2-dimensional images. I am constrained to 1.5 GB of RAM and I am
using the two for loops in an attempt to reduce the amount of data in
memory at any one time.
The program usually takes 4 days or more hours to run a set of 10,000
images compressed 4x, resulting in a voxel...PNG to PNG alpha (on Adjust)
I have a black-on-white greyscale PNG diagram which is antialiased on a
white background. I'd like to rejig it so I have a completely black PNG
with the 8-bit alpha channel being the original diagram. In other words the
black on the original diagram means 0% transparency and the white on it
means 100% transparency. So that effectively it gets anti-aliased onto
whatever colour I place it on (a blue background means a black-to-blue
Is it possible to do this with RISC OS? Adjust Paint does alpha sprites and
PNGs, but I can't work out how to write the alpha channel other than ...Further compress a already compressed file
My question is, can a compressed file be further compressed by
the same compression algorithm or other compresssion
algorithm? Why or Why not?
My experimental result is. Yes, it can be further compressed by a
considerably amount. (sometimes 50%)
Is that theoratically possible? This is against the impression I used
to have. Can some one kindly answer my question or give me some
- detailed description -------------------------------------
compression library : LZO
my data set : binary data.
I have a program that uses lzo library to com...