Pngcrush is a tool that lets you compress PNG images. Pngcrush optimizer for PNG (Portable Network Graphics) files can only be run from a command line in an MSDOS window, or from a UNIX or LINUX command line.
Its main purpose is to reduce the size of the PNG IDAT datastream by trying various compression levels an PNG filter methods. It also can be used to remove unwanted ancillary chunks, or to add certain chunks including gAMA, tRNS, iCCP, and textual chunks.
Neils has posted a way to include into context menu —here’s how to add a ‘Crush’ option to the context (right-click) menu in Windows Explorer for quicker crushing.
1. Open Control Panel and choose Folder Options. Select the File Types tab, and scroll down to the ‘PNG’ entry. Click on ‘Advanced’, then click on ‘New…’.
In ‘Action’, type Crush, and in ‘Application used to perform action’, type the following:
C:\Downloads\pngcrush\pngcrush.exe -e 2.png "%1"
The first portion should be the location of the pngcrush.exe file that you extracted from the archive. The ‘-e 2.png’ bit specifies what the outputted PNG image will be called, which in the case it’ll be the filename with ‘2’ appended to it (so the crushed version of ‘catpicture.png’ would be called ‘catpicture2.png’). You could also use the following:
C:\Downloads\pngcrush\pngcrush.exe -brute -e 2.png "%1"
This does the same as the above but does a ‘brute force’ crush - rather than use one of a few common methods to crush the file, it will use all of them. It’ll take longer, especially on older hardware, but may result in a smaller PNG file.
And you’re done. Now, when you right-click on a PNG file, you can select ‘Crush’ and have Pngcrush your image for you.