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pngslim
 - when every byte counts!

Andrew C.E. Dent, 2021.


Batch optimization of PNG images for MS Windows, using multiple tools to 
achieve the smallest file size, with scant regard for time.

WARNING: Although this software produces fully compliant PNG images, a
minority of image editors, viewers and certain mobile phones contain bugs
which may cause problems displaying these optimized images.


# Usage

1. Unzip the 'pngslim' folder and place in your chosen location.
2. Then just drag & drop* your PNG files on 'pngslim.cmd' to run.
3. Have fun slimming away those surplus bytes! :-)

* Note: Due to limitations of MS Windows, the maximum number of files that you
can drag & drop depends on the total text length of the image file paths+names.
If the script doesn't run or you see the following error message :
"Windows cannot access the specified device, path, or file...",
you should reduce the number of selected files (typically <100), and consider 
moving your files to shorten the path names (e.g. "C:\png\").


For advanced users please tweak the script to your needs.

- HuffmanTrials: When adjusting the number of Huffman blocks, the number of
 consecutive failed attempts to reduce file size, before quitting the trial.
 From testing 15 (default) works great, with higher numbers giving little
 benefit. For faster processing reduce to 2.

- RandomTableTrials : Number of trials with randomized Huffman tables (default 
100). To squeeze out a few extra bytes set to 500. For fast processing set to 1.

- LargeFileSize : The uncompressed file size in bytes that determines a small/
 large image and adjusts processing effort accordingly. The default 66400 bytes
 corresponds to an image larger than 128 x 128 pixels. 

- ForceRGBA : (0/1) will first rewrite the image as RGBA (32 bits per pixel)
 and then only optimize in that color mode, or restore the original if not 
 compressed. This limits the possible compression methods and may generate an 
 unneccessary alpha channel, so is not recommended (default is off ForceRGBA=0). 


# Legal

The software ('pngslim' script) is provided 'as-is', without any express or
implied warranty. In no event will the author be held liable for any damages
arising from the use of this software. Permission is granted to anyone to use
this software for any purpose, including commercial applications, and to alter
it and redistribute it freely*. The software is dedicated to the Public Domain.

The additional software included in the 'pngslim' package ('apps') is provided
for convenience. The additional software is the property of other authors and
may be subject to different licensing and legal conditions. Please check the
original authors' websites for details and latest information.

* The license for 'pngout.exe' restricts how the software may be distributed:
http://www.advsys.net/ken/utils.htm#pngoutkziplicense . Its inclusion is by
kind permission of K.Silverman and D.Blake. Therefore, you may not redistribute
the pngslim package with 'pngout.exe' without prior arrangement.


# History

v1.1 12-Sep-2021
- Added an early trial with OptiPNG, to losslessly reduce 16 to 8 bit per 
  channel. True 16bpc files are still rejected.
- Added ForceRGBA option. Certain applications require PNG files to be in the 
  RGB+Alpha color mode, at the cost of compression. Default is off.
- Added PNG validation: Basic file attributes tested (greater than 67 bytes); 
  File data checked with pngcheck on input and output.
- Hardened script against malicious filename input (names properly enclosed).
- Improved script readability: Indented with tabs; More consistent label and 
  variable naming; Expanded FOR loops over multiple lines; Avoid long lines 
  (<80chrs); External commands (executables) are identified with '.exe'.
- Fixed up typos and small details in Readme.
- Bundled programs will no longer be UPX compressed. The space saving is not 
  necessary and provides a minor speed up. Programs' license information added.
- Added 'pngcheck.exe' program v3.0.3 (25-Apr-2021) for file validation.
- Updated 'OptiPNG.exe' to v0.7.7 (was v0.6.3). Unpacked the distributed file,
  removing UPX compression. Various vulnerability fixes; Upgrades libpng and 
  zlib; Adds options -nx, -strip, -clobber, -debug; Changes the activity 
  display output from STDOUT to STDERR.
- Updated 'pngrewrite.exe' to version 1.4.0 (was 1.3.0). Maintenance release.
- Updated 'pngout.exe' to 13-Feb-2015 release (was 22-Sep-2009). This gives 
  better randomness when the -r switch is used; Fixes -f5 to generate block 
  boundaries in a consistent and correct manner; Adds -f6 option to reuse 
  filters line-by-line from a source PNG file.

v1.0 25-Sep-2009
- Release of version 1.0, with smarter, more efficient processing!
- Trial 1 to determine the best Color and Pre-filter type has been re-written.
This adjusts the effort used according to the size of the image. While this
should give a speed boost, it should *not* affect compression. Typically
compression should be equal or slightly improved. Let me know if this is not
your experience.
- With the re-write, some of the User variable were no longer necessary and
removed. The script requires less tweaking now and should work great for you
out of the box.
- Checked UPX compression of apps (v3.03W -ultra-brute -compress-icons=3).
Compressed 'pngoptimizercl' and 'pngrewrite'.

v1.0beta3 23-Sep-2009
- Update introduces first step in making the script a bit smarter and efficient.
- Bug fix, for setting the program path using the 'App' directory (from 1.0b2).
- Improved the routine for determining the optimum number of Huffman blocks, and
the Deflate strategy used by pngout. It should be noticeably faster for large
images, and may yield better compression in some cases.
- This is the first part of the script re-write, introducing improvements in
readability and the addition of debug/ geek feedback in the Verbose mode (v=0/1).

v1.0beta2 21-Sep-2009
- Small update release- no compression improvements.
- Reduced the default number of Huffman block trials saving time for large images
(MinBlockSize: 128 to 256bytes, LimitBlocks: 256 to 200 max). These are probably
more optimal settings.
- The color-filter trial tests less block thresholds (skip /b512), but this
should not affect final compression (Huffman blocks are optimized in Trial 2) and
helps improve speed.
_ Testing revealed that in rare instances the color-filter choice was not optimal
when using the quicker Pngout mode (/s1). The better but much slower mode is now
always used (/s0). For many users the original mode would be sufficient.
- More extensive color-filter trials with OptiPNG at 'stage24' may boost speed,
as less randomized trials will be tested with Pngout if OptiPNG is superior.
- Priority of Huffman trials (block number and random tables) increased from Low
to Below Normal for faster processing.
- Trial 3 updated to remove Pngout best strategy (/s0) which is already tested.
- Added the minimal 256byte zlib window size to final, ultimate OptiPNG trial.
- Tweaked compression trial 4 message to report number of trials (RandomTrials).
- Applications have been updated and placed in a separate 'apps' folder.

v1.0beta1 25-Mar-2008
- This update shifts the emphasis further towards compression, with even less
concern for speed / efficiency. More brute force trials are explored initially,
to avoid hitting local minima too early and then wasting time with later trials.
- As several changes have been implemented, this release is marked as a beta
awaiting feedback from the community.
- Renumbered the script stages ('01'>'10', etc.) for greater flexibility.
- Simpler detection of 16bpp / unsupported images using pngout's exitcodes.
- Added 'PngOptimizer' program which sets transparent (A=0) pixels to black and
often improves compression. Although this is technically a lossy process removing
color data, these regions will never be seen in the PNG image.
- It may no longer be necessary to include 'pngrewrite', but until this has been
tested, I will leave the script as is.
- More trials with some logic to determine best color and filter combination. As
a result 'stage20' has been subdivided. Grayscale images should be tested first,
with non-productive trials skipped. Please test my processing; comments welcome!
- Removed 'StartSize' variable and now reuse 'zs' as a general file size counter.
- Some longer running trials (Pngout) now run at low priority (start /low /b).
- Changed executable names to lowercase and removed '.exe' extension from script.
- After compressing each image, the percentage slimmed is now reported.
- Updated 'DeflOpt' (UPX compressed) and 'pngout' to latest versions.
- The following enhancements were suggested by 'fred01' (many thanks!):
- Script uses set- / endlocal, so should play nicer with batch scripting.
- If any of the bundled programs are not found, an error message is now produced.
- Zlib upgraded (1.2.2.1828 from AdvanceComp) to the latest version (1.2.3)
and then compressed with UPX 3.02. The main changes are security fixes, so
hopefully this wont cause any problems.

v0.91 21-Aug-2007
- Added 'VersionText' variable for identifying customized scripts (i.e. 'Fast',
'Extreme', etc.)
- Check added for detecting 'zlib.dll'.
- First step of uncompressing PNG with Pngout now always uses RGBA (-c6).
- Reordered trials in 'Stage02' and added a Pngout trial with some default
settings. This may occasionally find better color and filter parameters,
improving compression.
- Used UPX 3.01 (--ultra-brute) to compress the packaged software except for
pngout.exe and OptiPNG.exe (it seems the originals are already compressed).
- Updated 'readme.txt', reformatted for fixed width and included details of
'pngout' license.

v0.9 09-Jul-2007
- Fixed missing quotes for checking if required programs are present.
- Reduced range of Huffman blocks tested (Trial 2) for quicker processing.
- Slight syntax changes for future porting efforts.
- After Stage01 (where metadata is stripped), all further compression stages
have been set to preserve meta data (-k1). Hence, ancillary chunks can be kept
by editing the script to skip the first stage.
- Updated the included software to latest versions.
- Removed the 'pngexpand' script. I believe few users would benefit from it.
- Updated 'readme.txt'. Added warning for mobile phone developers.

v0.8 20-Jan-2007
- The pngslim directory is now set automatically by reading the directory of
the script and setting the executable search path to this directory. This
removes the need to edit the script manually; More user friendly.
- The minimum block size was increased to be more practical (64 > 128bytes),
reducing number of trials (hence time) for larger images.
- Unsupported formats of PNG files (e.g. 16bpp) are checked for and skipped.
- Window title is more compact for easier viewing when minimized.
- Added 'pngexpand' script to help avoid bugs in Photoshop and other editors.
- 'readme.txt' file cleaned up.

v0.7 04-Jan-2007
- Stage02: Initial compression with OptiPNG tests all filters (0-5).
- Stage02/Trial3: Added /s0 to test default Huffman tables and improve
compression before Stage03.

v0.6 01-Jan-2007
- First public release.


# Included programs

Note: I have no affiliation with the authors of the included software.
Please read the comments under the 'Legal' section of this readme.

- advdef.exe v1.15 (31-Oct-2005) by Andrea Mazzoleni.
   http://www.advancemame.it/comp-readme.html

- DeflOpt.exe v2.07 (05-Sep-2007) by Ben Jos Walbeehm.
   http://web.archive.org/web/20131208161446/http://www.walbeehm.com/download/index.html

- OptiPNG.exe v0.7.7 (27-Dec-2017) by Cosmin Truta.
   http://optipng.sourceforge.net/

- pngcheck.exe v3.0.3 (25-Apr-2021) by Alexander Lehmann, Andreas Dilger, Greg Roelofs.
   http://www.libpng.org/pub/png/apps/pngcheck.html

- PngOptimizerCL.exe v1.8 (6-Nov-2008) by H.Nilsson
   http://psydk.org/PngOptimizer.php

- pngout.exe (13-Feb-2015) by Ken Silverman.
   http://advsys.net/ken/utils.htm

- pngrewrite.exe v1.4.0 (8-Jun-2010) by Jason Summer.
   http://entropymine.com/jason/pngrewrite/

- zlib.dll v1.2.3 (18-Jul-2005) by Jean-loup Gailly and Mark Adler.
   http://www.zlib.net/


# Thanks!

Inspiration came from a script by JensRex ([email protected]) 11-Jun-2005
(http://hydrogenaudio.org/forums/?showtopic=22036).
Big thanks to: D.Blake, counting_pine, fred01, Greg Roelofs, markcramer, 
Ken Silverman, Sined, Thundik81, Cosmin Truta, UncleBuck, Zardalu and others.
Finally a massive thanks to all authors of the software on which this script
depends, and those pioneers developing and optimizing the PNG standard.


https://github.com/ace-dent/pngslim/releases