View source for Scratch-O-Gram

==Scratch-O-Grams or Hand Drawn Holograms==

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Scratch-O-Gram by Raul.

Scratch-O-Grams or Hand Drawn Holograms were first popularized by William J. Beaty in 1995. His article titled [[http://www.amasci.com/amateur/holo1.html Abrasion Holography]] is available on Science Hobbiest's website. A more technical paper by William J. Beaty was published by SPIE titled [[http://amasci.com/amateur/hand1.html Drawing Holograms by Hand]]. Tips for fabricating Scratch-O-Grams are [[http://amasci.com/amateur/holohint.html here.]] The definitive reference is:

W. T. Plummer and L. R. Gardner, "A mechanically generated hologram", Applied Optics Vol.31, No. 31 (1 November 1992) pp.6585-6588.

==Computer Help for Designing Hand Drawn Holograms==

Recently Holography Forum Member Raul provided a simple Visual Basic program for generating the scratch patterns from a 3D file. It currently works with small .3ds files or with .mcl files. .mcl files are created by a free program called MarbleCLAY and is available [http://homepage3.nifty.com/escargot/DownLoadFrm.html here]. Raul's program is called [http://www.holographyforum.org/files/3dS.zip 3dSilhouette]. The VB6 libraries are available [http://www.microsoft.com/downloads/details.aspx?familyid=7b9ba261-7a9c-43e7-9117-f673077ffb3c&displaylang=en  Here]. He has a web site [http://3dalter.50megs.com/ here].

It generates a pattern showing the length and placement of the compass for making the scratches for complex objects. It can also break the object into pages of equal length lines to speed fabrication.

==Here are the instructions from Raul:==

''This is the program for making patterns. It  is written in Visual Basic 6, and it needs some libraries. You need to download them or simply install VB6 on your PC. It works with .mcl, or.3ds input files. Mcl are marbleclay 3d files. Marbleclay can be freely downloaded from Internet, and is a very easy 3D editor.''

''You need to create a folder c:\3dSilhouette and extract files into that folder.'' '''The software will not run at any other path.'''

''Patterns are printed in letter format sheets, files are located in the OUT folder. Several files may be generated, depending on object complexity.''

''3d object can be rotated, moved and scaled. There is an option GetSilhouette that generates a wire frame model leaving only most important lines of the object for minimizing its complexity. You can then edit the object adding or erasing lines by simply double clicking on them.''

''Set render options:''

''XYScale –Vertical and Horizontal size of the object,''

''Min Radius, Max Radius –They define object depth''

''Left and Top margins – Is obvious.''

''Line and scratch spacing define hologram density. Try to set a bigger number to reduce the number of patterns.''

''Then you go to generate patterns, and render.''

''With Line Patterns, scratches are drawn putting the compass centre on the bottom  end of the lines and use line length as compass aperture. For horizontal lines, center compass in the right end. I use to make arc-shaped scratches with convexity looking to the top side of the sheet.''

'''One tip:'''

''If yow visualize the hologram in the way it appeared on the screen, image will go on deep. If you turn it upside down, image will pop in front of the sheet.'' 

'''Other tip (For Line Patterns)'''

''No matter that in even pages patterns appear horizontally all scratches are drawn the same way. In that cases you must center the compass in the right end of lines, and draw scratches in such a way that the tops of the arches aim to the top of the sheet. For vertical lines, it is more intuitive: center at the bottom and the top of arches matches with the top end with the lines.''

''Equal depth pages option was implemented lately following a suggestion of Adam Libura.''

''Program displays a page for each depth value (compass aperture) calculated. It is intended mostly for drawing on a transparency sheet laying directly on the lcd display screen. It displays a page of starting points for each compass aperture, which is shown in the left bottom corner of the page. You can use patterns right from Patterns window, or display bmp image files using windows image viewer. Pressing the button “Follow”, a cross pointer will navigate over the points to make it easier to find them correctly.''

'''One Suggestion:'''

''For drawing scratches in a transparency sheet, you can put the transparency on the sheet with pattern. Put compass tip on a piece of thick transparent plastic, to avoid damage the transparency. You can freely move the plastic piece on the transparency surface, to match the compass center with the bottom end of the lines. When lines are horizontal, center should be positioned at the right end of the lines.''

'''Another Suggestion:'''

''When viewing hologram, I backed it with a mirror, it help to increase brightness. I used to hang the hologram on the wall, at the height of the eyes, and illuminate it with a bright focus from a 3m distance. For viewing, I stayed 3m from the hologram, and focus hanged 20 cm over my head, in such a way that the focus slightly disappeared over the top border of the mirror.''

[http://www.youtube.com/watch?v=A40e2PgHPCQ U-tube Demonstration of a Scratch-O-Gram made by Raul]