I\'ve spent a long time trying to go from a CMYK EPS to a RGB PNG using RMagick and Rails. Hopefully this will be of use to someone:
def convert_image_from_
do you know about the paint_transparent command for RMagick?
image.paint_transparent(color, opacity=TransparentOpacity, invert=false, fuzz=img.fuzz) -> image
Description Changes the opacity value of all the pixels that match color to the value specified by opacity. If invert is true, changes the pixels that don't match color.
Arguments
color Either a color name or a pixel.
opacity The new opacity value, either an opacity value or a number between 0 and QuantumRange. The default is TransparentOpacity.
invert If true, changes all the pixels that are not the target color.
fuzz By default the pixel must match exactly, but you can specify a tolerance level by passing a positive value.
Returns A new image
Magick API TransparentPaintImage
Have you seen this video of railscasts http://railscasts.com/episodes/374-image-manipulation ? He uses the github logo to create a stamp with transparency.