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JPEG File Repair

(October 2002) posted on Wed Oct 09, 2002

Tired of spending hours trying to clean up low-quality JPEG files so that they're suitable for separating and printing?

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By Mark A. Coudray

3. If even the strongest Remove Artifacts setting doesn't remove all of the blocky artifacts, use just enough Blur Edges to remove the artifacts that remain.


4. Use the Add Grain slider to add back any surface detail lost during steps 2 and 3. Add the minimal amount of grain that creates the desired appearance.


Slider and button descriptions


The following descriptions clarify the purpose of the primary controls found in JPEG Repair.


Remove Artifacts This slider controls the strength of deblocking in the program (deblocking is 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.


Blur Edges This slider controls the amount of blur apparent on the dis-crete edges within the selected area of your image. Moving the slider to the right increases the amount of blur. Note that some blurring can help wipe out defects, such as extra-stubborn artifact edges. But too much can wipe out all detail from your image, so use the Blur Edges feature cautiously.


Add Grain JPEG Repair introduces subtle, organic noise-randomly placed blobs in the area of the image you select for enhancement. These blobs help recreate the natural surface textures of higher-resolution, uncompressed images. Moving the slider to the right yields a stronger pattern of dark blobs, so again, only use as much as needed to get the best results.


Randomize Grain To instantly change the arrangement of grain added to your selection, click this button. If you have not added any grain to your selection, this button will have no effect at all.


Correcting a corrupted image is a simple two-step process. The first step is to use the blur slider to soften the edges of the generated artifacts. This has a tendency to flatten the image and lower the overall contrast. But you can remedy this problem with the second step, which is to apply grain to the image until you achieve the desired look. Each of the correction functions are independent of each other, so if you find that applying the grain gives you the surface correction needed, but that some artifacts are still visible, simply increase or de-crease the blur slider and watch the correction in the preview.


Alien Skin offers some very helpful tips and techniques for using JPEG Repair. One is that you should not crop or resize your image before using the filter. Image Doctor relies on the regularity of the JPEG compression grid, which is altered when you crop or resize. Use JPEG Repair first; crop or resize second.


You can use JPEG Repair with or without a selection, but it is suggested that you use selections to separately treat the areas in your image with perceptibly different levels of damage. The JPEG compression effect is more noticeable in areas that are lighter in tone, like skin-tone values, than in darker areas, such as those representing dark hair. With an image that contains both types of graphic elements, applying the same strength of repair across the entire image may wash out some details that you wish to preserve in the hair. Ideally, you should select and treat the areas containing hair first, then repeat the procedure on the skin-tone areas.


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, so apply each function only as much as necessary to prevent creating an "airbrushed" appearance in the repaired image.


The 30-day full-function demo of Image Doctor can be downloaded from Alien Skin's Website at Demo's are available for both Mac and PC platforms.





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