The Secrets Of Photoshop Edge Detection
Edge detection in Photoshop is effectively invisible. Relatively few Photoshop users have ever delved into the inner workings of the lasso tool by clicking and holding on it so that the flyout menu pops out and allows you to choose from the standard lasso, the polygonal lasso, and the magnetic lasso.
Each one of these lasso tools has its uses. If you're trying to do a quick and easy selection and don't really care about the edges, the lasso is for you. If you're trying to select the 2001 monolith from a starry sky, then the polygonal lasso is your hot ticket. However, if you're trying to separate a single gargoyle from the mass of dancing gargoyles on the front frieze of the Minna stone temple, then you need the magnetic lasso and you need it badly.
Once you have selected the magnetic lasso all you need to do is to start playing with it to get the proper settings for your gargoylization surgery. The first thing you should do is hit the Caps Lock on your keyboard. This will change the silly looking lasso with a magnet icon to a much more useful circle with a crosshair. Not only will it be more accurate to be pixel perfect with the crosshair, but the software will only be examining the pixel values within the circle, rather than having to compute your entire image.
You can change the size of the circle to suit whatever you're doing. just look up to the Options Bar and change the width to whatever pixel setting you want. The smaller the setting, the more accurate the edge detection. You can change sizes on the fly with the ] and [ keys. Try it. It's neat!
When you're working with low contrast images (like the monolith against the starry sky) you'll want to play with the Option Bar's Contrast setting. The lower the setting, the better it will detect low contrast edgings. Change this setting on the fly with the . and , keys.
You can also tell Photoshop how often you want anchor points dropped with the Frequency value on the Option Bar.
Now magnify the beejeezus out of the image. In my Photoshop CS4 I love to work with the 600% setting. At this magnification, the pixels are clearly delineated so it's easy to switch mags back and forth to make sure you're working with the right pixels.
Once you start working with the tool you'll see why it got its magnetic name. As you drag along close to the edge you're trying to select, the trailing tail will adhere to the edge it recognizes quite magnetically, and drop anchor points where it sees fit. If you're trying to round a specifically tight corner or are passing an area of low contrast to the background, just click and you'll drop anchor points wherever you want them.
If you happen to put an anchor point in the wrong place, don't start again. Just hit the Backspace key (Delete on the Mac) and start eliminating anchor points in reverse order. Very handy for those huge jobs. Those gargoyles on the Minna temple are huge! Some are bigger than Ryan Hupfer's chin!
Hey! I can make fun of Ryan. He doesn't work here anymore and he doesn't have my address.
You can switch between lasso tools too with the Alt key (Option on Mac) but don't. It's mostly not necessary and generally screws you up.
When you get to the end of your image, the typical lasso tiny circle will appear and you can close off your selection and introduce the magnificent Adobe marching ant parade.
Now you can copy the selection to another layer or file and you can repeat the process for any dropouts from within the image such as holes in earrings, etc. Pretty soon you've got a perfectly selected image to drop in anywhere you want. Remember to adjust the selection's contrast, brightness, curves, hue, saturation, etc. to look like it really belongs on the new background.
In some cases I like to manually blur my edges with the smudge tool set at one or two pixels. Just drag the smudge along the side of the image to keep that nasty jagged pixilization from making your image look like it was dropped in. For an even better effect, merge your image into the background layer then do the smudge runaround and you'll be able to fool FBI photographic specialists. It's extremely handy for fulfilling all your Forrest Gumpian fantasies. Ever wanted a photo of you standing naked next to Marilyn Monroe? Go for it!
This Hub is for nicomp who requested it and to thank him for tipping me off that his cousin Mine That Bird was the hot pick for the Kentucky Derby (I knew that wasn't a light fixture but a birdhouse)!