[Java] How can I cut an image using a color pattern?

Question

Hi there, my name is Daniel and I'm from Spain.

I am developing a small program which cuts images by the color.

That's will be easiest to explain using an example image. I have got this image:

http://dl.dropbox.com/u/944667/Ejemplo1.png

And I want to create a new image just with the purple form, without the black frame.

Does anyone have any idea? I am using Java 2D so I think that I need to create an Object "Shape" with the purple area of the first image.

Thank you!!!

Best regards, Daniel.

Answer 1

You need to use some flood-fill algorithm that finds the boundries of the purple area:

Wikipedia has a page on it with excellent pseudo code and animations.

http://en.wikipedia.org/wiki/Flood_fill

Answer 2

If the image is literally like the one you show, you could:

• load the image into a BufferedImage (with ImageIO.read())
• create a new BufferedImage of the same size, ensuring it has an alpha layer (e.g. set its type to BufferedImage.TYPE_4BYTE_ABGR)
• "manually" go through each pixel in turn in the loaded BufferedImage, getting the pixel colour with getRGB() and checking if it's black
• if the colour is black, set the corresponding pixel to transparent in the new image, else to the original colour from the first image (see setRGB() method)
• save the new image (with ImageIO.write())

There are fancier ways, but this simple method is nice and understandable and will work fine for images of the type you showed.