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kornelski / pngquant

Lossy PNG compressor — pngquant command based on libimagequant library
https://pngquant.org
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Question about GPL license. #332

Closed margox closed 5 years ago

margox commented 5 years ago

Hi! I am developing a picture compression program that supports multiple formats, which uses pngquant(in fact, I am using a bin wrapper named pngquant-bin which licensed under MIT).

I want to know if I open the source code of my app on github, then do I have the right to sell my app without buying your commercial license?

kornelski commented 5 years ago

I think pngquant-bin's license information is misleading, because GPL applies to it, too.

You have the right to sell GPL-licensed software, but you don't have a right to stop anyone from distributing it further (i.e. also selling your program, or giving away for free the copy they bought).

You need the commercial license if you want ability to keep your source secret and/or prevent others from sharing the program.

margox commented 5 years ago

It's a little difficult for me to buy a commercial license right now. If I usepngquant as an optional plug-in for my app, open the source code of the plug-in, and let the user decide whether or not to install the plug-in, will my app not be subject to the GPL? If my app can be sold later, I will be able to purchase commercial license.

jibsen commented 5 years ago

IANAL, but you might find the GPL FAQ useful, for instance:

https://www.gnu.org/licenses/gpl-faq.html#GPLWrapper https://www.gnu.org/licenses/gpl-faq.html#NFUseGPLPlugins

You may need legal advice to figure out what constitutes a combined program.

margox commented 5 years ago

The articles you listed above helped me a lot! Thank you very much!