Understanding the cause and effects of JPEG Artifacts (as well as being able to recognize them) is very important to the quality of your images. The jpg format is a very popular and widely used format. It’s great for small files used on websites and for emailing because it can load and send faster. However, despite the usefulness it can have, saving an image in the jpeg format also comes with some not-so-great side effects.
The JPEG format uses a lossy compression method during saving. This means that when you save your image as a .jpg some of the [unnecessary] data from the original image file is discarded and your image is saved with a reduced file size. The quality that is lost (discarded) from your image can not be recovered. In addition, each time you save your image more data is lost and image quality reduced. This is also very common with images taken on mobile devices such as camera phones and for many point-and-shoot cameras.
The degradation of image detail can appear as:
1. Blockiness or checkerboarding
2. Mosquito noise
3. Color degradation – false color or color changes
4. Dark color degradation around sharp edges
Every single JPEG image exhibits these characteristics to some degree, and the more compressed your image is the worse it will be.
Besides lowering image quality, the presence of jpeg compression artifacts can have negative effects on your post processing. Applying creative and corrective enhancements to an image plagued with compression artifacts will cause your adjustments to not be as clean and crisp as they should be. So, it is always best to start with a clean image before making any creative or corrective enhancements – this will ensure optimal quality of your final image.