Anti-Aliasing

Anti-aliasing of images is a bit tricky to describe, though for compensating for low resolution images, it is a helpful trick to be aware of. As described in an earlier post relating to limitations with resolution for web images, sometimes things can look more clear by being more blurry. Anti-aliasing works in a similar way.
     Aliasing refers to the unwanted "jagged" look that can be seen with pixels in high contrast areas of an image. The closeups below show a comparison between an image (top) with aliasing, and one (below) with anti-aliasing. Though the resolution (pixels per inch) is the same for both of these, the one with anti-aliasing appears more clear.

The terminology and methods used for enabling anti-aliasing may differ depending on the program being used. This may be found as an option within paint programs, layout programs, PDF generating settings, settings for merging layers, as filters, as effects, etc. Regardless of how it is found within the programs, the main point of this article is to point out its positive effect when used for certain types of images.
    The examples below is from a scanned document which consists primarily of only high contrast text and graphics. By name, "anti-aliasing" was not used through any of the tools or options available to me in the paint program I was using. What was done instead was to adjust the tones of the image in such a way as to manually have less aliasing in the image.

The sample above (top) is with tones adjust to soften the edges between the areas of black and white. Basically some of the gray is allowed to remain as a thin layer of division between the two contrasting colors. If this is removed (second example above), and the tones are adjusted for more contrast between the black and the background white, the image becomes much more "jagged" and rough looking. (And in addition, as seen in the illustrative areas of the image, some detail is lost.)  

Above is an even closer view that more clearly shows the tones being used between the areas of high contrast. As noted earlier, even though the resolution (pixels per inch) remains the same for each, the illusion of added clarity seems greater for one over the other. It is odd to think that the blurry looking one ends up appearing more clear and detailed. 
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Note, earlier post on sharpening filters also relates to perceiving added clarity through seemly odd ways. The two of these kind of go hand-in-hand, and are of interest for both web publishing (where resolution of images is limited) and for print production (for optimizing image quality).    

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Sharpen Filter

    The labeling of this photo editing trick is a bit odd. The term "unsharpen mask" is a term from days when film was shot and darkrooms were used for processing and printing photographs. The name is misleading though I am sure there was a reason for it at the time. Rather than for making something look more "unsharp" (more blurry and out of focus), it is actually for adding more clarity - to make more "sharp" - with details more pronounced rather than less.
     Another fascinating aspect of this trick is that it was evident at a much earlier time as seen in the artwork of Spanish Renaissance painter El Greco (a favorite of mine). Rather than having one area of color align cleanly with another area of a different color, the division between the two can appear more distinct (when seen from a distance) through the use of thin bands of different tones and opposing colors. The result being the illusion and perceiving of added clarity - lines of division between areas becoming more pronounced rather than less.
   

Original scanned photo lacking focus and clarity.

With a limited amount of sharpening added. Though subtle, 

there is some added clarity. 

With an extreme amount added. Though drastic in its effect, this example does show how different bands of varying tones are added to bordering areas of shades (such as on porch roof, end of stairs, wall areas around windows, etc.).   

Another before and after example, enlarged.  

   
     There is obviously a limit to how much clarity can be artificially added. Those TV programs showing photo editing tricks being used for reading license plates from blurry photos take from miles away, are just a bit too good to be true! This being said, this type of "sharpening" is a handy tool and trick to have for improving clarity with images.
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(Image: family photo, corner store in Sinnemahoning, PA.)
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