How do I crop an image using a color pattern?

Question

I am developing a small program that slices images by color.

It's easiest to explain with this example image:

black with a purple splotch of color

And I want to create a new image with only purple shape, no black border.

Does anyone have any ideas? I'm using Java 2D, so I believe I need to create a Shape object with a purple area of the first image.

+2

dafero 05 May '10 at 11:10

2 answers

You need to use some kind of fill algorithm that will find the borders of the purple area:

Wikipedia has a page with excellent pseudocode and animation.

+2

aioobe 05 May '10 at 11:20

Neil coffey · Accepted Answer · 2010-05-05T11:21:45+0000

If the image literally looks like the image you are showing, you can:

load the image into BufferedImage (with ImageIO.read ())
create a new BufferedImage of the same size, ensuring that it is at alpha level (for example, set its type to BufferedImage.TYPE_4BYTE_ABGR)
"manually" traverses each pixel in turn in the loaded BufferedImage, getting the pixel's color using getRGB () and checking if it's black
if the color is black, set the corresponding pixel to transparent in the new image, otherwise the original color from the first image (see the setRGB () method)
save new image (using ImageIO.write ())

There are more fun ways, but this simple method is nice and straightforward and will work great for the type of images you showed.