Java Image Quality (JPEG)

Is it possible to get the current quality of an existing image?

I want to load a JPEG and save it again without any change in quality and DPI. (I need to 开发者_如何学Pythondo some pixel manipulation before saving)

JPEG is a lossy format.

The direct way to do this, read the image, do what you need to do, reencode the image, will result in the image being slightly deteriorated.

That said, if that is fine, then you need to know that the way that quality works in JPEG encoding, is to determine how much information to keep about contrast. The less quality, the less sharp a transition you can have. In other words, this is not a single setting enclosed in the JPEG-file, but a setting determining the number of image data saved.

What you can do is to say that the final image need to be around the same size as the original. You can then encode the result at different quality settings and choose the one giving the image size you want.