Search found 30 matches: tweakpng

Searched query: tweakpng

by XnTriq
Sat Jan 18, 2020 9:00 am
Forum: Classic - Bug Reports
Topic: [Solved] Problem viewing certain PNG files
Replies: 3
Views: 3131

[Solved] Problem viewing certain PNG files

TweakPNG's validity check gives these PNGs a clean bill of health, and I can open them in Photoshop, Firefox etc., but XnView Classic/MP and MS Paint don't like them:
by XnTriq
Tue Sep 12, 2017 10:30 pm
Forum: New
Topic: Can't Open File
Replies: 44
Views: 3508

Re: Can't Open File

Brother Gabriel-Marie wrote:Right now I'm stuck with files that won't display, and I have no idea why. I can see them with any other program; just not MP. When I open a "broken" file in another program, say, Imagine (I use it as a plugin in FreeCommander) then it opens it fine. Photoshop opens them fine, too and nothing seems to be wrong with them.
I successfully opened your sample files with two dozen or more programs (including XnView MP). None of them had any problems whatsoever loading these images. Even all the diagnostic software I use on a regular basis (JPEGsnoop, TweakPNG, and Stuffware Photo Studio, to name but a few) gave them a clean bill of health.
by XnTriq
Sun Dec 25, 2016 4:30 am
Forum: Classic - General Support
Topic: Addons -> PNGOUT
Replies: 14
Views: 3138

Re: Addons -> PNGOUT

SharkD wrote:Do you know which browsers support grayscale+alpha channel? Because even if XnView does not support it, it still might be a good idea to use it on my website.
They're widely used, …
… and all modern web browsers support them “out of the box”.
Can I use… ([url=http://www.caniuse.com/#feat=png-alpha]PNG alpha transparency[/url] » Known issues) wrote:IE7 & 8 do not support PNG's alpha transparency when you apply CSS alpha filter on them or a parent element.
Useful tools:
by XnTriq
Sat Nov 26, 2016 3:45 am
Forum: Classic - Bug Reports
Topic: 2.39: Error opening png file
Replies: 5
Views: 988

Re: 2.39: Error opening png file

Welcome to the forum, Stepa_ua.

I can confirm that XnView Classic v2.37 and v2.39 as well as MP v0.83 don't like SoftJig.png. I had no problem viewing it with v1.99 though, and TweakPNG gives it a clean bill of health.

Update:
Windows Picture and Fax Viewer
Windows Picture and Fax Viewer
p136095.png (19.37 KiB) Viewed 977 times
by XnTriq
Sun Nov 20, 2016 11:15 pm
Forum: Classic - Bug Reports
Topic: 2.39: Gimp-made images crash XnView
Replies: 18
Views: 1960

Re: 2.39: Gimp-made images crash XnView

I don't have any problems opening Gradient.png either.
The file does not contain any metadata or a color profile.
TweakPNG wrote:

Code: Select all

Chunk | Length | CRC      | Attributes                | Contents
------+--------+----------+---------------------------+----------------------------------------------------------------
IHDR  |     13 | c69676e4 | critical                  | PNG image header: 640×400, 8 bits/sample, truecolor, interlaced
gAMA  |      4 | 0bfc6105 | ancillary, unsafe to copy | file gamma = 0.45455
bKGD  |      6 | a0bda793 | ancillary, unsafe to copy | background color = (255,255,255)
pHYs  |      9 | 009a9c18 | ancillary, safe to copy   | pixel size = 2835×2835 pixels per meter (72.0×72.0 dpi)
tIME  |      7 | 9d44472a | ancillary, unsafe to copy | time of last modification = 20 Nov 2016, 16:10:12 UTC
iTXt  |     29 | 642e6507 | ancillary, safe to copy   | text (international), key=“Comment”: “Created with GIMP”
IDAT  |   8192 | ce24ebab | critical                  | PNG image data
IDAT  |   8192 | 5191baca | critical                  | PNG image data
IDAT  |   8192 | 540c47ef | critical                  | PNG image data
IDAT  |   8192 | c1d270d1 | critical                  | PNG image data
IDAT  |   8192 | cd761d6d | critical                  | PNG image data
IDAT  |   8192 | 8ed13a12 | critical                  | PNG image data
IDAT  |   8192 | 1b6981a5 | critical                  | PNG image data
IDAT  |   8192 | 17a0503c | critical                  | PNG image data
IDAT  |   8192 | fa66f225 | critical                  | PNG image data
IDAT  |   8192 | f07a856b | critical                  | PNG image data
IDAT  |   8192 | 45b33ff2 | critical                  | PNG image data
IDAT  |   8192 | cb3d0844 | critical                  | PNG image data
IDAT  |   8192 | 3d0abd63 | critical                  | PNG image data
IDAT  |   8192 | 329de0f7 | critical                  | PNG image data
IDAT  |   8192 | 48a98318 | critical                  | PNG image data
IDAT  |   8192 | 880cd8f4 | critical                  | PNG image data
IDAT  |   8192 | b88cd8b2 | critical                  | PNG image data
IDAT  |   8192 | e720b281 | critical                  | PNG image data
IDAT  |   8192 | 395bd9da | critical                  | PNG image data
IDAT  |   8192 | bc6dac1a | critical                  | PNG image data
IDAT  |   8192 | 4e437488 | critical                  | PNG image data
IDAT  |   8192 | e4a4c4c8 | critical                  | PNG image data
IDAT  |   1322 | 11c5c22d | critical                  | PNG image data
IEND  |      0 | ae426082 | critical                  | end-of-image marker
by XnTriq
Sat Nov 12, 2016 6:45 am
Forum: Classic - General Support
Topic: Way to produce a transparent canvas?
Replies: 6
Views: 1051

Re: Way to produce a transparent canvas?

p135768.zip
(2.77 KiB) Downloaded 42 times
Contents of attachment:
  • 0_Example.png
    1_XnView_Truecolor+Alpha.png
    1_FireWorks_Truecolor+Alpha.png
    1_SuperPNG_Truecolor+Alpha.png
    2_XnView_Palette+Index.png
    2_FireWorks_Palette+Index.png
    2_PNGOptimizer_Palette+Index.png
    3_TweakPNG_Truecolor+tRNS.png (Ignored by XnView)
    4_FireWorks_Palette+Alpha.png (Supported by XnView since v1.97)
cday wrote:you might like this thread: https://www.diybookscanner.org/forum/vi ... 236#p20235
Maybe you have a better solution to the originating problem in the first post of the thread? :wink:
Will do :mrgreen:
by omniplex
Mon Jan 18, 2016 7:44 pm
Forum: Customization
Topic: Open with...
Replies: 0
Views: 3670

Open with...

XnView has an "open with" feature, i.e., if you right-click on a file you can select "open" F3 or "edit" F4 to get the same effect as in Windows explorer "open" or "edit". For images this is rather boring, "open" in explorer on my box starts XnView, so when I am already in XnView I rarely need F3. It is possible to define additional "open with" programs in XnView for any file, e.g., a hex. viewer better than the XnView built-in hex. viewer.

Disadvantages, when you want to get rid of a bad "open with" idea XnView only offers to delete everything, back to only F3 and F4. An additional "open with" tool works for any file, you cannot define something only for, say, PNG. Recently I decided that I want an "open command prompt here" feature also within XnView. And after that worked as expected I modified it to open tweakpng for PNG, or a command prompt for everything else. Eventually I arrived at a script opening exiftool -k for ICC / MIE / XMP, or dcraw -i -v for camera raw.

If you want similar "open with" functions you can copy and edit the code shown below, save it in a tools folder, where you have exiftool / dcraw / tweakpng / etc., and define it as "open with" application in XnView. For the latter XnView first offers to open an *.exe, but it is a simple plain text *.cmd, you have to select * to see all files including *.cmd, not only *.exe and also not only *.bat. The name doesn't matter, I use OPENDIR.cmd:

Code: Select all

@setlocal enableextensions & echo off
if not "%~2" == ""     call "%~0" "%*"
if not "%~2" == ""     goto :EOF
if     "%~1" == ""     goto HELP
if     "%~1" == "?"    goto HELP
if     "%~1" == "/?"   goto HELP
if     "%~1" == "-?"   goto HELP
set PADD=%~dp0;%PATH%;.
set NEED="%~1"
if not exist "%~f1"    goto NEED
set NEED="%~f1\."
if     exist "%~f1\*"  goto OKAY
set NEED="%~f1\.."
if /I "%~x1" == ".ICC" goto EXIF
if /I "%~x1" == ".ICM" goto EXIF
if /I "%~x1" == ".MIE" goto EXIF
if /I "%~x1" == ".PNG" goto PING
if /I "%~x1" == ".ARW" goto CRAW
if /I "%~x1" == ".CR2" goto CRAW
if /I "%~x1" == ".CRW" goto CRAW
if /I "%~x1" == ".DNG" goto CRAW
if /I "%~x1" == ".ERF" goto CRAW
if /I "%~x1" == ".KDC" goto CRAW
if /I "%~x1" == ".KRO" goto CRAW
if /I "%~x1" == ".MEF" goto CRAW
if /I "%~x1" == ".MRW" goto CRAW
if /I "%~x1" == ".NEF" goto CRAW
if /I "%~x1" == ".NRW" goto CRAW
if /I "%~x1" == ".ORF" goto CRAW
if /I "%~x1" == ".PEF" goto CRAW
if /I "%~x1" == ".RAF" goto CRAW
if /I "%~x1" == ".RAW" goto CRAW
if /I "%~x1" == ".RW2" goto CRAW
if /I "%~x1" == ".RWL" goto CRAW
if /I "%~x1" == ".SR2" goto CRAW
if /I "%~x1" == ".SRW" goto CRAW
goto OKAY
:EXIF --------------------------------------------------------------
set NEED=exiftool.exe
for %%x in (%NEED%) do if exist "%%~f$PADD:x" set NEED=%%~f$PADD:x
if     exist "%NEED%"  goto CALL
set NEED=exifgui.exe
for %%x in (%NEED%) do if exist "%%~f$PADD:x" set NEED=%%~f$PADD:x
if     exist "%NEED%"  goto OPEN
if not exist "%NEED%"  goto NEED
:PING --------------------------------------------------------------
set NEED=tweakpng.exe
for %%x in (%NEED%) do if exist "%%~f$PADD:x" set NEED=%%~f$PADD:x
if     exist "%NEED%"  goto OPEN
if not exist "%NEED%"  goto NEED
:CRAW --------------------------------------------------------------
set NEED=dcraw.exe
for %%x in (%NEED%) do if exist "%%~f$PADD:x" set NEED=%%~f$PADD:x
if not exist "%NEED%"  goto NEED
call "%NEED%" -i -v "%~f1"
goto WAIT
:OPEN --------------------------------------------------------------
start "%~n0" /D . "%NEED%" "%~f1"
goto :EOF
:CALL --------------------------------------------------------------
call "%NEED%" "%~f1"
goto WAIT
:NEED --------------------------------------------------------------
echo/
echo Error: %~nx0 found no %NEED%
:HELP --------------------------------------------------------------
echo Usage: %~nx0 FILE
echo/
echo Default action:  Open a command window (CMD.EXE) in the folder
echo of the specified existing FILE or subdirectory.
echo/
echo Edit this script to run another program depending on the FILE
echo extension, e.g., for a PNG start TWEAKPNG.EXE, or for MIE start
echo EXIFTOOL.EXE.
echo/
:WAIT --------------------------------------------------------------
set NEED="%CMDCMDLINE:)=%"
for /F "usebackq tokens=2" %%c in ('%NEED%') do if %%c == /c pause
goto :EOF
:OKAY --------------------------------------------------------------
endlocal & cd /D "%NEED%" & cmd /k title %~nx0
by omniplex
Mon Jan 11, 2016 9:25 pm
Forum: Classic - Bug Reports
Topic: certain PNGs cannot be saved
Replies: 9
Views: 3906

Re: certain PNGs cannot be saved

XnTriq wrote:Trying to do so with m96yxdgsf6j8.png
[...]
still results in an “error writing the file”.
2.35 can save this. The text chunks are gone (as promised), some 72 dpi pHYs chunk appears out of thin air, and the colour profile isn't identical (original: 2627 bytes, saved: 2520). Maybe libpng "upgrades" known colour profiles on the fly. :?

Unrelated, tweakpng is still at version 1.4.6, and I think its "import colour profile" feature is broken. But it can import complete colour profile chunks (exported from another PNG). Truepng.exe is at version 0.6.1.8, but I haven't tested yet if that fixes a truepng bug with odd PNG formats (IIRC 16bits grayscale didn't work for me with truepng 0.5.1.4.)
by XnTriq
Wed Dec 30, 2015 10:15 pm
Forum: Classic - Bug Reports
Topic: Error saving PNG
Replies: 18
Views: 6745

Re: Error saving PNG

Welcome back, omniplex :-)
omniplex wrote:
XnTriq wrote:
...
Can someone please confirm?
WFM.
THX.
omniplex wrote:Presumably you know deark mentioned in another thread, there is a working Windows 64bits binary in the tarball.
I knew about Jason Summers' site and use some of his software (TweakPNG in particular). deark escaped my notice, though. Wow! Danke for the hint :D
omniplex wrote:Something else you presumably know, but I didn't see it in the plugin thread, there are some free and some shareware Simple Filter plugins by a German photographer. The free versions work for me in XnView. The XnView ICC option claims to affect JPEG and TIFF, but actually it also works for PNG:
I've actually posted a link to SimpelFilter before but I failed to realize that they also have LE editions which are free. So again: Thank you for pointing this out!
omniplex wrote:The XnView ICC option claims to affect JPEG and TIFF, but actually it also works for PNG:

[…]

source
Interesting series of articles by SimpelFilter's head honcho 8)
(It's too bad that Heise had to shut down their UK operations.)
by XnTriq
Sat Dec 06, 2014 11:30 am
Forum: Classic - Bug Reports
Topic: certain PNGs cannot be saved
Replies: 9
Views: 3906

Re: certain PNGs cannot be saved

omniplex wrote:
XnTriq wrote:TweakPNG
Brilliant tool, I planned to add this to the "other software" forum as a thank you for lots of interesting links (today I read something about JPEG ELA forensics), but obviously you know TweakPNG already. I could post two scripts for the TweakPNG "tools" feature, combining PNGwolf+TruePNG (if anybody uses that, maybe Dos386.)
I'm glad to hear that you find the links useful, omniplex! (I assume you're referring to JohnFredC's topic about image quality.)
TweakPNG has proven indispensable when it comes to solving PNG mysteries. There's lots of other cool stuff to explore on Jason Summers's site!
omniplex wrote:
XnTriq wrote:XnView will resave sample.png without error, if Use ICC Embedded Profile (JPEG/TIFF) - Very slow (Tools » Options... » General » ICC) is activated.
Good to know, as it happens I have that, together with an "sRGB intent saturation" default. Kudos.
BTW: PngOptimizer discards the iCCP, pHYs as well as the tEXt chunks and combines all IDATs.
by omniplex
Thu Dec 04, 2014 7:14 pm
Forum: Classic - Bug Reports
Topic: certain PNGs cannot be saved
Replies: 9
Views: 3906

Re: certain PNGs cannot be saved

XnTriq wrote:TweakPNG
Brilliant tool, I planned to add this to the "other software" forum as a thank you for lots of interesting links (today I read something about JPEG ELA forensics), but obviously you know TweakPNG already. I could post two scripts for the TweakPNG "tools" feature, combining PNGwolf+TruePNG (if anybody uses that, maybe Dos386.)
XnTriq wrote:XnView will resave sample.png without error, if Use ICC Embedded Profile (JPEG/TIFF) - Very slow (Tools » Options... » General » ICC) is activated.
Good to know, as it happens I have that, together with an "sRGB intent saturation" default. Kudos.
by XnTriq
Wed Nov 26, 2014 12:00 am
Forum: Classic - Bug Reports
Topic: certain PNGs cannot be saved
Replies: 9
Views: 3906

Re: certain PNGs cannot be saved

xnview wrote:i can't reproduce :(
Here's the xnview.ini I use for my tests:

Code: Select all

[Cache]
IsActive=0
SavingMode=1

[Start]
ParamsSavingMode=1
SavingMode=1
Deleting the iCCP chunk (“Artifex Software sRGB ICC Profile”) with TweakPNG enables XnView to resave sample.png.
TweakPNG ([color=green]default_rgb.icc[/color]) wrote:

Code: Select all

Compressed size: 2341
Uncompressed size: 2576

― Header ―
Profile size: 2576
Preferred CMM type: “”
Profile version: 2.1.0
Profile/device class: “mntr”
Data color space: “RGB ”
Profile connection space: “XYZ ”
Profile creation time: 0-00-00 00:00:00 UTC
Profile file signature: “acsp”
Primary platform: “APPL”
Embedded profile flag: 0
Dependent profile flag: 0
Device manufacturer: “”
Device model: “”
Attributes: Reflective, Glossy, Positive, Color
Rendering intent: 0 (Perceptual)
Illuminant: X=0.96419, Y=1.00000, Z=0.82489
Profile creator: “”
Profile ID: 00000000000000000000000000000000

― Tags ―
Number of tags: 10
Tag #1 signature=“desc” offset=252 size=124 type=“desc”
	“Artifex Software sRGB ICC Profile”
Tag #2 signature=“cprt” offset=376 size=40 type=“text”
	“Copyright Artifex Software 2011”
Tag #3 signature=“wtpt” offset=416 size=20 type=“XYZ ”
	X=0.95045, Y=1.00000, Z=1.08905
Tag #4 signature=“bkpt” offset=436 size=20 type=“XYZ ”
	X=0.00000, Y=0.00000, Z=0.00000
Tag #5 signature=“rXYZ” offset=456 size=20 type=“XYZ ”
	X=0.43607, Y=0.22249, Z=0.01392
Tag #6 signature=“gXYZ” offset=476 size=20 type=“XYZ ”
	X=0.38515, Y=0.71687, Z=0.09708
Tag #7 signature=“bXYZ” offset=496 size=20 type=“XYZ ”
	X=0.14307, Y=0.06061, Z=0.71410
Tag #8 signature=“rTRC” offset=516 size=2060 type=“curv”
Tag #9 signature=“gTRC” offset=516 size=2060 type=“curv”
Tag #10 signature=“bTRC” offset=516 size=2060 type=“curv”
CreativeWorld ([url=http://newsgroup.xnview.com/viewtopic.php?p=115823#p115823]2.12 XnView: PNG resize[/url]) wrote:XnView versions after 2.05 are unable to (re)save some (?) PNGs, just creates an empty output file and exits without any messages (silently crashes?).
Sample file: http://i58.fastpic.ru/big/2013/1206/fe/ ... 40fffe.png
<--// EDIT //

XnView will resave sample.png without error, if Use ICC Embedded Profile (JPEG/TIFF) - Very slow (Tools » Options... » General » ICC) is activated.

// EDIT //-->
by XnTriq
Tue Jul 29, 2014 11:00 pm
Forum: New
Topic: IPTC/XMP Editor does not save metadata in PNG files
Replies: 18
Views: 2414

Re: IPTC/XMP Editor does not save metadata in PNG files

Extracted from 14584184510_0e8e56a51d_o_d.png with TweakPNG:

Code: Select all

Chunk | Length | CRC      | Attributes                | Contents
——————+————————+——————————+———————————————————————————+—————————————————————————————————————————————————————————————————————————
IHDR  |     13 | e2c59e60 | critical                  | PNG image header: 111x111, 8 bits/sample, truecolor+alpha, noninterlaced
sBIT  |      4 | 7c086488 | ancillary, unsafe to copy | significant bits/sample: R:8,G:8,B:8,A:8
pHYs  |      9 | 3d6683c7 | ancillary, safe to copy   | pixel size = 787x787 pixels per meter (20.0x20.0 dpi)
tEXt  |     25 | 9bee3c1a | ancillary, safe to copy   | standard text: [Software]=[www.inkscape.org]
tEXt  |    496 | 9076c43d | ancillary, safe to copy   | nonstandard text: [Raw profile type iptc]=[…]
tEXt  |   3674 | 7fd4a41d | ancillary, safe to copy   | nonstandard text: [XML:com.adobe.xmp]=[…]
IDAT  |   3867 | 20a7ea0a | critical                  | PNG image data
IEND  |      0 | ae426082 | critical                  | end-of-image marker
tEXt chunk ([color=green]Raw profile type iptc[/color]) wrote:

Code: Select all

IPTC profile
     222
4e616d651c0250000642796c696e651c0255000c42796c696e65207469746c651c025a00
04436974791c025c00084c6f636174696f6e1c025f000553746174651c02640003555341
1c02650007436f756e7472791c0267001f4f726967696e616c207472616e736d69737369
6f6e207265666572656e63651c02690009486561646c696e652e1c026e00076372656469
74731c02730006536f757263651c02740009436f707972696768741c0278001a43617074
696f6e2c2063617074696f6e2c2063617074696f6e2e1c027a000e43617074696f6e2077
726974657200
tEXt chunk ([color=green]XML:com.adobe.xmp[/color]) wrote:

Code: Select all

<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="XMP Core 5.1.2">
   <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
      <rdf:Description rdf:about=""
            xmlns:Iptc4xmpCore="http://iptc.org/std/Iptc4xmpCore/1.0/xmlns/">
         <Iptc4xmpCore:CountryCode>USA</Iptc4xmpCore:CountryCode>
         <Iptc4xmpCore:Location>Location</Iptc4xmpCore:Location>
      </rdf:Description>
      <rdf:Description rdf:about=""
            xmlns:dc="http://purl.org/dc/elements/1.1/">
         <dc:creator>
            <rdf:Seq>
               <rdf:li>Byline</rdf:li>
            </rdf:Seq>
         </dc:creator>
         <dc:description>Caption, caption, caption.</dc:description>
         <dc:rights>Copyright</dc:rights>
         <dc:title>Object Name</dc:title>
      </rdf:Description>
      <rdf:Description rdf:about=""
            xmlns:photoshop="http://ns.adobe.com/photoshop/1.0/">
         <photoshop:AuthorsPosition>Byline title</photoshop:AuthorsPosition>
         <photoshop:CaptionWriter>Caption writer</photoshop:CaptionWriter>
         <photoshop:City>City</photoshop:City>
         <photoshop:Country>Country</photoshop:Country>
         <photoshop:Credit>credits</photoshop:Credit>
         <photoshop:Headline>Headline.</photoshop:Headline>
         <photoshop:Source>Source</photoshop:Source>
         <photoshop:State>State</photoshop:State>
         <photoshop:TransmissionReference>Original transmission reference</photoshop:TransmissionReference>
      </rdf:Description>
   </rdf:RDF>
</x:xmpmeta>
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                                                                                                    
                           
<?xpacket end="w"?>
Android the Andrew wrote:While looking at this, I noticed in the Info pane, under the Exiftool tab, under the Exiftool heading, there's a warning:
Warning Bad Photoshop IRB resource "\x20Cap"
I hope this information is somehow helpful in identifying the problem.
by cday
Mon Jul 28, 2014 1:47 pm
Forum: NConvert
Topic: copy png to png expands palette
Replies: 7
Views: 2408

Re: copy png to png expands palette

dlang wrote:Using -colors <numColors> is not practical when I am converting a bunch of images using a DOS "for" loop command.

Code: Select all

for %f in (*.png)  do nconvert -o out\%f  %f
Is not practical because... ? It doesn't run, or some other reason?
I also do not know the number of color used in each image.
If you open an image in a GUI image editor such as XnView you should be able to see the image properties including the number of colours, or you could upload an example image.[/quote]
I used tweakPng to display the file details and noticed the palette size increased.
But that shows the number of colours??

When a png file is opened NConvert may convert it to a 24-bit image while preserving the actual colours used; when you use the -colours option you would need to set a value equal to greater than the number of colours in the original image.
I am using nconvert to strip off some of the meta chunk sections (text, iText, and zText).
You should be able to do that using the following flag:

-rmeta : Remove Metadata (EXIF/IPTC/...)

Have you created a list of the available NConvert commands using -help ?
by dlang
Mon Jul 28, 2014 1:13 pm
Forum: NConvert
Topic: copy png to png expands palette
Replies: 7
Views: 2408

Re: copy png to png expands palette

Using -colors <numColors> is not practical when I am converting a bunch of images using a DOS "for" loop command.

for %f in (*.png) do nconvert -o out\%f %f

I also do not know the number of color used in each image.
I only determined that nconvert was expanding the palette because some of my images got larger (size on disk).
I used tweakPng to display the file details and noticed the palette size increased.

I am using nconvert to strip off some of the meta chunk sections (text, iText, and zText).