Android如何在不损失质量的情况下将png格式的图像转换为jpeg格式

Question

I develop an app which involves a step of uploading image to server.But the server only support jpeg format image,so I have to convert the png format images picked or captured by users on client side.So I use the follow codes do this image format transformation:

bitmap.compress(Bitmap.CompressFormat.JPEG, 100, outputStream);

but some images will loss quality,compared to png format and the eyes can see the loss.Does this method has some bugs?Are there some good methods to do png to jpeg transformation without loss quality in Android?

Answer 1

JPEG is a lossy compression format, it will have data loss. See the post here:

Saving JPEG files in Android with no loss of pixel information

The idea behind "compression" is to reduce the file size, but there is always a tradeoff. You may try increasing the size of the PNG file and then doing "compression" - but then you may need to scale it back down and you are back where you started.

NOTE: PNG is not "lossy" and is "compressed" compared to some other formats, eg Bitmap. I originally posted with the assumption that compression = lossy, but some formats are considered "compressed" simply because they require less storage and without loss. For example, Zip is a file format that will change file data organization to store them with less space and without loss.

This is a different type of compression from what JPEG does, which alters the information in order to "compress" the file, and store it in a smaller file. Compression of this type is fundamentally different.