Removing JPEG Artifacts in Photoshop

When digital camera images—or any other images for that matter—are saved as highly compressed JPEGs, you will have to contend with the presence of JPEG artifacts. These artifacts are often in the form of compression artifacts in the pixel patterns. Here you will learn what to do—and even more important, what not to do—when working with these types of images:

1. Open and make a copy of the Cowboy_RGB image.
2. Zoom in on the cowboy’s face. You will clearly see a rectangular pattern of compression artifacts in the pixels. These are groups of pixels that have similar values. The loss of image detail that has resulted from this JPEG compression cannot be reclaimed. But what you can do is decrease the visual effects of the compression artifacts that have been created. Apattern of posterized pixels has recognizable edges. Choose Filter --> Sharpen --> Unsharp Mask, and assign the following values: Amount = 100, Radius = 1, Threshold = 0. Click the Preview button to witness the disturbing results. Notice how the JPEG pattern of compression artifacts is exacerbated by the sharpening. The sharpening attacks the edges of compression artifacts pattern just like any other high-contrast edge. So don’t do this! Always soften the artifacts prior to sharpening. You will want to get in the good habit of zooming in and checking for these JPEG patterns of compression artifacts before sharpening these compressed images.
3. While still zoomed in with the compression artifacts patterns visible, choose Filter --> Blur --> Gaussian Blur. The Gaussian Blur dialog box appears.
4. Set the Gaussian Blur radius initially to 0.1.
5. While watching the compression artifacts in the pixels, start raising the Gaussian Blur radius in 0.1 increments. At around 0.3 to 0.4, you will see a dramatic softening of the JPEG pattern of artifacts. How much blur you should apply depends on the amount of posterization in the image.

Sharpening after Removing Artifacts
After you have softened the pattern of JPEG degradation, you can carefully apply some sharpening to regain some image focus:

1. While still zoomed in and watching both the high-contrast edges and the smoother skin tones, choose Filter --> Sharpen --> Unsharp Mask.
2. Assign the following Unsharp Mask values: Amount 50 Radius 1 Threshold 3–5 View the results of this sharpening.
3. While carefully watching the skin tones to monitor the return of any posterization, apply the same amount again, and perhaps even a third time. Applying your sharpening incrementally like this affords you more control over the final results. One final tip here: always check your image at 100% view before you accept the final results. Although you may want to zoom in to inspect how the sharpening affects the image at the per pixel level, viewing your image at 100% provides you with the best approximation of what this image’s sharpness and focus will look like when printed. At 100% view, your image should look slightly sharper onscreen than when printed. Remember, not all of this sharpening will make it through the printing process, because printing in general softens your image.

Well, there you have it, a whole set of smoothing and sharpening skills, tools, and techniques that you can use to improve the quality of your print images. By mixing and matching these various skills, tools, and techniques, you should be able to tackle just about any noise or sharpening challenge. And as you gain experience working with your own images, you can fine-tune these techniques to suit your needs. In time you will no doubt develop your own methods. My final suggestion for you is to always evaluate your images prior to making adjustments. Take time to zoom in and look through the channels. With a thorough image evaluation, you will save yourself lots of time flailing around with inappropriate tools or techniques. Ultimately, you will work faster and achieve better results.