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cachemash #209: TUTORIAL | by eaubscene
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cachemash #209: TUTORIAL

cachemash tutorial

by H.Manon


Cachemashing is my name for a somewhat more controlled approach to what Daniel Temkin identified as the Photoshop Truncating Glitch—an approach to image glitching that exploits a problem with early versions of Photoshop. Cachemashing is in my view a relatively pure or true form of glitching, because my control over the outcome is limited almost exclusively to the selection of input files, and to standard user-end changes to Photoshop settings. Once these decisions are made, Photoshop glitches a truncated jpeg file in ways that are difficult and at times impossible to predict. However, what makes this technique compelling is that, through practice, one may nonetheless develop and refine a personal approach, even if the final cause of the glitch remains opaque—a mystery taking place behind-the-scenes of Photoshop’s interface.


I want to preface what follows by saying that I am not a programmer. Although I am fairly savvy as a Photoshop user, my understanding of the program’s internal workings are almost nil. I'm sure if I knew more about the causes of this technique I would be less interested in it. The fun here is really in the "not knowing why."


In this tutorial I mainly describe how I arrived at the image above (a glitched “Currier and Ives” style print of a duck hunt). These specific techniques could be altered in numerous ways and still produce the effect of a cachemash.


What you need to cachemash:


1) Photoshop 6.0 or earlier. I am running Photoshop Elements 1.0, which is the Elements version that corresponds with PS 6.0. My system is Windows XP, and I know that the technique also works when Photoshop 6.0 (or PE 1.0) is installed on Vista. I have not tested this technique on any other OS.


2) A truncated jpeg file in which the point of truncation appears close to the top, resulting in a mostly “blank” image when opened in PS. Jpegs are easy to truncate using code editing programs like Notepad++. My approach is to open the jpeg in Notepad++, delete a couple of lines of data somewhere just below the file header, save, and then open in PS. You have succeeded when you open the file and receive the golden message “This document may be damaged (the file may be truncated or incomplete). Continue?” Sometimes it takes ten or so tries to successfully truncate the file, rendering it partially damaged, but not too damaged to open.


3) At least one non-truncated image file that you want to form the mashed-up content of the final image. These are the files you will load into the PS cache.


4) A computer that has sufficient speed and RAM to process the size of image you want to produce.


The procedure:


1) Open a truncated jpeg in Photoshop. The truncated file I used for the “duck hunt” cachemash is 4500 x 4822 pixels @ 300 ppi. The compression rate of the truncated file does not seem to matter. The original image content also does not seem to matter, since the truncation renders it blank.


2) The message pops up: “This document may be damaged (the file may be truncated or incomplete). Continue?” Click OK. You will see a blacked-out image, with perhaps a tiny line of color at the top (depending on how near to the top you truncated the file).


3) Now is when you can get creative, in a fascinatingly limited way. Open any file or set of files. Manipulate them as usual in PS, or not. Then close them. For the “duck hunt” image, I pre-sized a jpeg at a width of 8984 (almost but not quite twice the width of the truncated file). This is the trick to obtaining something like a “full frame” cachemash in which the cached image is fully or mostly visible in the final version.


4) Use the filter called Gaussian Blur on the truncated file. A blur radius setting of 0.1 pixels is ideal. This procedure “fixes” the mashed image, in the photographic sense of the word; it stabilizes the data which, up to now, tended to load randomly into the void space of truncated file. The result is a mash-up of certain files and parts of files that have been temporarily stored in the PS cache. (Note: I use Gaussian Blur at 0.1 because of all the possible filters, this one seems to least alter the final image, while still “fixing” it. However virtually every PS filter will "fix" a truncated file).


5) The truncated file is now cachemashed. If you like the results, save to the file format of your choice.


6) Undoing the Gaussian Blur returns the truncated file to its volatile state.


7) Redoing the Gaussian Blur will give new results each time. However (and this is what makes the technique really interesting), the more you undo and redo, the more your “fixed” images also become part of the PS cache. You might think of this as “caching the cache.” If you undo and redo fifty times, the image will be really minced up. But, if at any point you open a new non-truncated jpeg in PS, that jpeg will become part of the cache, and may appear largely in tact as a portion or layer of the mashed image.


Some other tips and observations:


1) In the process of doing and undoing, you will see that when the PS cache attempts to “fill in” the truncated image, it does so in a cycle. The length of the cache cycle is controlled by the size of the cache you elect in Preferences > Memory & Image Cache. I mostly keep cache levels set at 8 (this is max) and RAM used by PS set at 100%. Striking embroidery-like effects can be achieved by reducing RAM used by PS down to 15% or so.


2) Incorporating high contrast RGB images (color or b/w, doesn’t matter) yields brighter colors in the final “fixed” version. Low contrast images produce subtler, more muted colors.


3) Introducing Inverted (i.e. negativized) images to the cache produces interesting results, as do images to which Gradient Map has been applied.


4) It is very unusual to produce a final cachemash that is grayscale, but it sometimes happens.


5) The non-truncated sliver of the truncated file will appear as a black band at the top of the final “fixed” version. I usually crop this out, but this is the only post-processing I do. All of the other effects in images I have posted to Flickr happened prior to the moment of glitching, which I take to be the moment at which PS “fixes” the images.


6) It is possible to create the same cachemash twice. Just open the same files in the same order with the same settings on the same machine. This suggests that there is nothing random about cachemashing. At the same time, if you begin by caching an image that is even one pixel larger or smaller, the results after several cycles of do-and-undo could be radically different.


7) If you overlay the PS crop tool on top of a truncated file, and there is data in the cache, the space within the cropped area will weirdly animate. When you press “crop,” the animation will stop because the image is now fixed.


8) When the final colors you achieve are saturated reds, blues and greens, it is sometimes possible to experience the optical illusion called chromostereopsis.


I will continue to add observations on this page as they come to me.


Good luck!



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Taken on August 10, 2012