On Sun, 23 Aug 2009 23:39:32 -0700 (PDT), wrote:
Is there a way with Photoshop 7 to closely crop a light bulb .jpg image where when finished, you have only the outline of the light bulb versus a square image that contains the light bulb image?
Another solution might be if the square was cropped closely with everything outside the bulb being transparent. Not sure if this is possible and haven’t been able to find much on the subject so thought I’d ask here.
Yes, it’s possible. The final image will be square, but with transparent areas outside the bulb.
You will also need to save in a file format that supports transparency.
Here are two ways:
Erase and Delete
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1) Double alt-click on the background layer, turning it into a normal layer that supports transparency.
2) Use the eraser to erase the area outside the bulb. You can also select areas with the lasso tool, and delete them if that’s faster, the use the eraser to get rid of the unwanted material.
3) Save in a file format that supports transparency. This includes png, tif, and psd. Gif format supports only on/off transparency, and will result in a jagged edge.
Layer Mask
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1) Double alt-click on the background layer, turning it into a normal layer that supports transparency.
2) Add a layer mask
3) Paint the layer mask black in the areas outside the bulb
4) If you go too far, you can do a mid flight correction by painting white.
5) Save in a file format that supports transparency. This includes png, tif, and psd. Gif format supports only on/off transparency, and will result in a jagged edge.
There are any number of tricks to make the job easier. You may find Save for Web (which I believe is there in PS 7) easier to use than saving in an explicit file formate. The magnetic lasso is sometimes extremely useful for selecting the edges of an object. Sometimes the image itself contains information that can be used as the transparency mask – you may need to use the levels command to get a clean black/white distinction, and clean up with a brush afterward.
If you notice a black or white fringe when you use the image, google for the concept of pre-multiplied alpha (which Photoshop uses for external image storage), and matte color. When saving the image for later compositing outside of Photoshop, you will need to pick a matte color, which should match the background as closely as possible. —
Mike Russell –
http://www.curvemeister.com 
