Note: This only works for pictures that have a solid background color, like blue.
1) Open up a pic you want to use. I would reccomend a high resolution picture if possible. Sharpen it if it looks good. For this example, I am going to use a Kenyon Martin photo:
http://img25.imageshack.us/img25/5425/preview15xz.jpg
2) Use the Magic Wand tool to highlight the background.
http://img438.imageshack.us/img438/5855/preview21lo.jpg
3) Feather the image with a one pixel radius. To do this, select the select tool, right click, and click feather.
4) Next, go to "Select" on the top bar, then "Modify", then "Contract". You want to contract it with 1 pixel radius.
5) Press delete six-eight times. I personally use seven. This is your result:
http://img273.imageshack.us/img273/7335/preview38iy.jpg
6) You're not done yet. You need to make a new layer and place it behind your picture. Fill this layer with black to see if there are any spots that the crop missed. Use the one pixel eraser to get rid of them if there are any.
http://img273.imageshack.us/img273/3015/preview45ox.jpg
7) Delete the black layer. Resize the image to a appropriate size (more or less 150 x 150 pixels for http://www.hoopsvibe.com/nba/nba_players/index211.html pictures)
8) Paste it on to a 128 x 128 layer. Save it as a .png file. You now have your .png file for the portrait you will be making.
