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Home >> Photography >> Guest Articles Genuine
Fractals Stairstep Resizing Technique - A
Comparison of Image Enhancement with Bicubic and Genuine Fractals Stair-step
Techniques It is becoming fairly well known to many people involved with image sharpening problems that one can often achieve quite good results by successive resizing in a number of small steps -say 8 or 10 - to achieve a final enlargement goal of perhaps 200% of the original size. This is generally referred to as stair-step resizing and until now has been almost exclusively confined to "bicubic" resizing as found in various Photoshop and PaintShopPro imaging programs. In these programs implementation is fairly straightforward. For example if one resizes by successive 109% steps it takes just a hair over 8 steps to achive a final 200% size increase. It will then be found that the resultant image is often noticeably clearer than that which can be achived by normal image sharpening filters. Hence this particular method of stair-step resizing has come into a fair amount of use recently. Not generally known but of great interest to this writer who has developed and applied the technique. is that the stair-step procedure can also be used with fractal image procedures such as Genuine Fractals, which is available as a plug-in for both Photoshop and PaintShopPro, the editor I normally use. One of the primary purposes of this article is to compare the degree of improvement in image clarity which can be achieved by these two stair-step enhancement methods. Further improvement is shown to be achievable by the additional application of the well-known unsharp mask filter. In the actual implemention of the stair-step methods dealt with here it should be noted that whereas the bicubic stair-step resizing is fairly quick and easy to do, not so with Genuine Fractals. This is not too difficult to explain but invoves a number of awkward steps which can easily lead to mistakes and can certainly be frustrating. I have included 3 composite images each involving five operations, Consider now the first image which was made from a web image with my own camera type - the Sony F707.
In image (A) I simply doubled the original crop size using the bicubic resize feature in PaintShopPro7 to provide for easy comparison with the following 4 images. Image (B) was easy again using bicubic resize value to 109% and applying it 8 times to get barely under 200% and then a final pixel count resize to get an even 200%. This first operation is quite easy to do. Getting image (C) was a bit more involved. Using the Genuine Fractals program I first opened the image - which had been saved in the .stn format under the simple name "temp1.stn" - at a size of 100%. Then I saved this using the same file name and closed it. Then I reopened it again with a size of 109% and saved it again. I repeated these operations for a total of 8 times to get just under 200% and then opened a final time at the pixel size correspomding to an even 200% and gave it a final save before transferring it to a file name chosen for the final stair-step result. Images (B) and (C) provide a direct comparison of stair-step resizing with the bicubic method and Genuine Fractals and there were noticeable differencesm which to this writer appeared to favor the latter method. A further difference was that one could apply a conventional image sharpening filter such as the well known unsharp mask filter to create further sharpening. I applied this in image (D) to the bicubic result and in image (E) to the Genuine Fractals image. In this case there seemed to be a significant improvement in (E) versus (D), mainly I feel because the line detail seemed to be smoother in the Genuine Fractals case and this facilitated this further sharpening. The other two examples below, were treated in exactly the same way and the results were fairly comparable with the fractal method apparently superior in each case. The differences are particularly evident if the images are examined under somewhat increased mgnification. Questions about Robert's method can be sent directly to him. Also by Robert Sturrock - Removing Halo Effects from Sharpened Images Edwin's comment - Robert's method of applying stair-step increases via Genuine Fractals seemed quite similar in quality offered by Extensis' pxl SmartScale application. There is a similarity in the manner in which the edges become pronounced, leading to apparent improvement, especially when seen at an appropriate viewing distance.
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