JPG Compression

When an image is saved as a JPG (or JPEG) file, it is saved with some level of compression. Unfortunately, JPG uses "lossy compression", unlike a PNG image which is bigger but does not lose image quality. The lower the JPG compression, the higher the image quality will be. Conversely, the higher the JPG compression, the lower the image quality becomes.

How compression affects an image

Here is the same image saved using two different compression settings. We have enlarged both versions to 200% to show the pixel information. If you look carefully at the image on the right, you can see 8 × 8 squares — a clear indication of excessive JPG compression.

Woman saved as a high-quality JPG with low compression — Highest quality (lowest compression)

Woman saved as a low-quality JPG with high compression — Lowest quality (highest compression)

Use the highest-quality source available

To avoid losing too much of the original pixel information, save JPG images using the highest-quality (lowest-compression) setting available in your software.

When Focus Magic saves an image as a JPG, it uses the highest quality and lowest compression possible. If you open a JPG image and Focus Magic detects a high level of compression, it warns you that the image may be low quality and that your result may not be as good as it could be. Whenever you work with JPG images, try to use the highest-quality copy available.

For more technical information, see lossy compression.