Skip to main content

linux - Convert image to uncompressed PNG from the command-line


I have a compressed PNG image compressed.png. I can convert it to an uncompressed PNG decompressed.png using GIMP (saving as PNG and setting compression level to 0). How can this be done on the command line (Linux)?


I recall doing this in the past using Imagemagick's convert, but I forgot how. I tried some things that I thought should work based on the documentation:



  • convert compressed.png -compress None decompressed.png

  • convert compressed.png +compress decompressed.png

  • convert compressed.png -quality 0 decompressed.png

  • convert compressed.png -quality 00 decompressed.png


just wrote an ordinary compressed PNG.


Aside: why would you want an uncompressed PNG?


Some cases:



  • You want to support efficient (binary) diffs of the image data, while still using other features of the PNG format (as opposed to storing raw image data or BMP).

  • You want to compress several PNGs together in a tarball or 7z archive, but want to keep using PNG features. If the images are sufficiently similar this can give a better compression ratio than compressing individually.

  • Useful as a baseline size for testing PNG optimizers.



Answer



ImageMagick will always compress PNG files. The worst compression you can get is using:


convert -verbose -quality 01 input.png output.png

but it depends on the image content (the 0 will use Huffman compression which sometimes compress better than zlib).


You can try other tools like pngcrush (http://pmt.sourceforge.net/pngcrush/) to disable the compression:


pngcrush -force -m 1 -l 0 input.png output.png

which create a file the same size GIMP create when using Compression Level 0 (few bytes more or less).


Some example sizes (for a photographic PNG, 1600x1200):



  • original: 1,693,848 bytes.

  • after IM: 2,435,983 bytes.

  • after GIMP: 5,770,587 bytes.

  • after pngcrush: 5,802,254 bytes.


Comments

Post a Comment

Popular Posts

Use Google instead of Bing with Windows 10 search

I want to use Google Chrome and Google search instead of Bing when I search in Windows 10. Google Chrome is launched when I click on web, but it's Bing search. (My default search engine on Google and Edge is http://www.google.com ) I haven't found how to configure that. Someone can help me ? Answer There is no way to change the default in Cortana itself but you can redirect it in Chrome. You said that it opens the results in the Chrome browser but it used Bing search right? There's a Chrome extension now that will redirect Bing to Google, DuckDuckGo, or Yahoo , whichever you prefer. More information on that in the second link.
Post a Comment
Read more

linux - Using an index to make grep faster?

I find myself grepping the same codebase over and over. While it works great, each command takes about 10 seconds, so I am thinking about ways to make it faster. So can grep use some sort of index? I understand an index probably won't help for complicated regexps, but I use mostly very simple patters. Does an indexer exist for this case? EDIT: I know about ctags and the like, but I would like to do full-text search. Answer what about cscope , does this match your shoes? Allows searching code for: all references to a symbol global definitions functions called by a function functions calling a function text string regular expression pattern a file files including a file
Post a Comment
Read more

How do I transmit a single hexadecimal value serial data in PuTTY using an Alt code?

I am trying to sent a specific hexadecimal value across a serial COM port using PuTTY. Specifically, I want to send the hex codes 9C, B6, FC, and 8B. I have looked up the Alt codes for these and they are 156, 182, 252, and 139 respectively. However, whenever I input the Alt codes, a preceding hex value of C2 is sent before 9C, B6, and 8B so the values that are sent are C2 9C, C2 B6, and C2 8B. The value for FC is changed to C3 FC. Why are these values being placed before the hex value and why is FC being changed altogether? To me, it seems like there is a problem internally converting the Alt code to hex. Is there a way to directly input hex values without using Alt codes in PuTTY? Answer What you're seeing is just ordinary text character set conversion. As far as PuTTY is concerned, you are typing (and reading) text , not raw binary data, therefore it has to convert the text to bytes in whatever configured character set before sending it over the wire. In other words, when y...
Post a Comment
Read more

linux - CentOs 7.1 - Install Tomcat 8

I am using this tutorial as a setup reference to getting a Tomcat 8 running on CentOs 7.1 , but after typing: [root@localhost tomcat]# sudo systemctl start tomcat I get the error: Job for tomcat.service failed. See 'systemctl status tomcat.service' and 'journalctl -xn' for details. systemctl status tomcat.service prints the following: [root@localhost tomcat]# systemctl status tomcat.service tomcat.service - Apache Tomcat Web Application Container Loaded: loaded (/etc/systemd/system/tomcat.service; disabled) Active: failed (Result: exit-code) since Wed 2015-11-25 16:54:33 CET; 1min 19s ago Process: 45873 ExecStart=/opt/tomcat/bin/startup.sh (code=exited, status=203/EXEC) Nov 25 16:54:33 localhost.localdomain systemd[1]: Starting Apache Tomcat Web Application Container... Nov 25 16:54:33 localhost.localdomain systemd[1]: tomcat.service: control process exited, code=exited status=203 Nov 25 16:54:33 localhost.localdomain systemd[1]: Failed to start Apache Tomcat Web App...
Post a Comment
Read more