JPEG Repair

Table of Contents

JPEG compression separates an image into 8x8 (pixel) rectangles, then independently compresses each rectangle. The result of a poor use of JPEG compression is an ugly, repetitive pattern of blocks. Over-compression can take place when an image is saved as a JPEG in computer software, like Photoshop, or when an image is snapped at low-resolution in hardware, like a digital camera. JPEG Repair reduces the damage caused by over-compressing screen-resolution JPEG image files, making damaged images more aesthetically pleasing.

Note: It is impossible to restore details from the original uncompressed image—details that were lost in the compression process. JPEG Repair reduces the visual impact of over-compression.

Before

After

This chapter contains the following sections:

Using JPEG Repair

Use the following procedure to use JPEG Repair:

1. Select the area to be repaired.

2. Starting from the lowest setting, increment the Remove Artifacts slider until the perceptible blocky defects of JPEG compression have been removed. Do not overuse.

3. If even the strongest Remove Artifacts settings do not remove all of the blocky artifacts, use just enough “Blur Edges” to remove the remaining artifacts.

4. Use the “Add Grain” slider to add back any surface detail lost during Steps 2 and 3. Use only as much grain as needed.

Slider and Button Descriptions

Remove Artifacts

This slider controls the strength of “deblocking” in JPEG Repair—the reduction of rectangle-shaped artifacts in highly compressed JPEGs. Moving the slider to the right strengthens the deblocking effect. You might assume that selecting the highest value would give you the best results. This, however, is not the case. Excessive “Remove Artifacts” values result in an unnaturally soft appearance in your image. Don’t smear too much Vaseline on the lens. Use only as much artifact removal as necessary.
Range: 1 – 100

Blur Edges

This slider controls the amount of blur apparent on the discrete edges within your selection. Moving the slider to the right increases the amount of blur applied. Some blur can help wipe out defects, such as extra stubborn artifact edges. Too much can wipe out all detail from your image. Use Blur Edges cautiously.
Range: 1 – 20

Add Grain

JPEG Repair introduces subtle, organic noise—randomly placed blobs in your image or selection that help recreate the organic surface textures of higher-resolution, un-compressed images. Moving the slider to the right yields a stronger pattern of dark blobs. Again, only use as much as needed to get the best results.
Range: 0 – 20

Randomize Grain

To instantly change the arrangement of grain added to your selection, click this button. If the “Add Grain” slider is set to 0, the “Randomize Grain” button is disabled.

Tutorials

Using Multiple Selections to Repair a JPEG

Sometimes, JPEG compression artifacts seem perceptibly stronger in different areas within an image. It is best to separately select and filter these areas. By treating all damaged areas the same, you risk losing detail in the less damaged areas of your image.

Use the following procedure to get the best results when using multiple selections.

1. Identify the areas of your image containing visually similar damage. The image below provides a simple example of how damage can look different in parts of an image. In this picture, the yolks exhibit more damage than the whites.

2. Select one of the visually similar areas.

3. Perform JPEG Repair on this selection and click OK.

4. Repeat steps 2 and 3 until you have removed the JPEG artifacts from your image.

Tips and Tricks

Do Not Crop/Resize Images Before Using JPEG Repair

JPEG Repair relies on the 8x8 pixel regularity of the JPEG compression grid. Cropping or resizing your image will limit the effectiveness of the filter. Use JPEG Repair first, then crop or resize.

Using JPEG Repair with Selections

You can use JPEG Repair with or without a selection, but we suggest using selections to separately treat the areas in your image with perceptibly different levels of damage. For example, skin may exhibit stronger artifacts than hair. Applying the same strength of repair to the entire image may wash out some details that you wish to preserve in the hair. In this case, you should select and treat the hair first, then repeat the procedure on the skin-toned areas.

Do Not Overuse JPEG Repair

JPEG Repair is extremely easy to use. With only three sliders to adjust, it’s hard to screw up. It’s also an easy filter to overuse. Use it only as much as necessary to prevent creating an “airbrushed” appearance in your repaired image.