问题
I'm going to create a new JPG image with PHP. How can I set the DBi value of a new JPG image.
Dirk
回答1:
JPG is a Pixel format that doesn't really know physical dimensions like Dots Per Inch.
All you can do is write a dpi value into the file's Metadata as assistance for further processing, but it's just a recommendation and it can't be done using the GD library.
You would have to use an third-party library for this. See e.g. the second answer to this question: How do I add exif data to an image?
来源：https://stackoverflow.com/questions/5077189/how-to-define-dpi-for-a-new-jpg-image