I had a question concerning jpg image creation ImageIO.write(imgStega, "jpeg", file) : I am doing some steganography, and I have to hide data in least significant bit of each pixel. I do this with getRGBA()[pos], which provide me Red, Blue, Green, Alpha components. Then I change each value with a +1 or -1 depending on a %2.
The problem is, every time I use ImageIO.write, it changes all my image at random (it is compressing). So, how can I save my image as it is ? I don't see any solution to do steganography on a real image.
Whether I use png or jpg is the same, the weight changes. Do you know a way to save my image the way it is ?
Thanks in advance !
JPEG is lossy by definition, so the data modifications that you see are expected and there is not much you can do about it in your context.
On the other hand, PNG is also compressed but in a lossless manner. The size of the png file changes because the png compression is similar to regular file compression (called LZ): very grossly explained, it detects repeated byte patterns and encodes them in fewer bytes. Changing the bytes of your image changes these patterns, and this may change the efficiency of the compression. You could as well see an increase in size. But when an application opens your modified image, it should see exactly the bytes that you have stored.
Is the change of size a concern because this might allow someone to detect your modifications? In that case, I don't see any other solution than using only uncompressed formats.