[magick-users] Summary: drop shadow

[Andrew Graham]

Here is a summary of this thread.

Goal
Add a drop shadow to an image, from the command line.

Method
convert -depth 8 -threshold 0 -negate source.png 
    -bordercolor white -border 20x20 -gaussian 0x3
    -shave 15x15 - | composite -gravity northwest 
    source.png - out.png 

Adjustments
- Set the background color with:
    -bordercolor <color>
- Set the color of the drop shadow by adding:
    -colorize <r>/<g>/<b>
  before -negate, where <r>, <g>, and <b> are the 
  percentages of red, green, and blue of the desired color.
- Adjust the amount of blur with:
    -gaussian <radius>x<sigma>
  I find values from 0x3 to 0x5 to be useful.
- Empirical method to adjust the drop shadow's offset:
  Set the parameters of -border to four times the desired offset in
  pixels, and the parameters of -shave to three times the desired offset.

Notes
- The command is one line, wrapped for the mail message.
- The source image is referenced twice in the command line.
- This method fails when the amount of blur is greater than 
  the offset of the drop shadow.

Andrew Graham 
using IM 5.4.7 on WinXP.