Reduce JPEG Artifacts

Most digital images are stored as JPEGs. JPEG allows you to compress the original image into a much smaller file size. However, this does come at a price: JPEG artifacts. If an image is highly compressed, JPEG artifacts become quite obvious. Even if an image is not compressed at a high ratio, the JPEG artifacts can become quite obvious when it is enlarged or sharpened.

The image at the top shows, at 200% zoom, a portion of an image compressed with JPEG quality of 25 (out of 100). The JPEG compression artifacts are quite obvious. In the blue sky you can see the tell-tale “blockiness” of JPEG compression. At sharp edges such as the windmill and tree line, there are small speckles around the edges. These are very typical instances of JPEG compression artifacts.

Topaz DeJPEG™ can effectively suppress JPEG compression artifacts. Just apply the filter and set “Suppression” to 80 (keeping the rest of the parameters at default values). You will immediately see that all the JPEG artifacts are gone. The figure below the original image is the filtered image using Topaz DeJPEG™. The filtered image sometimes tends to look a little bit soft. Change the “Sharpen” to 1.5 to compensate for the loss in sharpness. The table below is the complete filter parameter setting.

Topaz DeJPEG™ is very straightforward. There is only one key parameter, “Suppression”. The higher the value, the more JPEG artifacts it can suppress. However, do not set it higher than necessary since it also makes images softer.

To compensate for the softness due to JPEG artifact suppression, Topaz DeJPEG™ integrates a simplified version of Topaz Sharpen™. This sharpening function is controlled by three parameters, “Sharpness” in the “Main” tab page, “Sharpen Radius” and “Edge Crispness” in the “Advanced” page. Please refer to section Sharpen Images for more detailed discussion. In many cases, Topaz DeJPEG™ alone can produce satisfactory results. In other cases, especially when the original images are highly compressed; you may want to take the full advantage of the more advanced Topaz Sharpen™. In this case, leave the “sharpness” and edge crispness value at 1.0 (default value) and apply Topaz Sharpen™ after Topaz DeJPEG™.

For images compressed with JPEG2000, Topaz Vivacity™ contains another filter, Topaz DeJPEG2000™, that is specifically designed to reduce JPEG2000 artifacts. Usage is similar.