iOS and Android Algorithm or library for feathering edges of the images similar to photoshop's

Question

I am looking for iOS and Android library for (preferably) or algorithm that would help me to feather edges of the image in similar way how it is handled in Photoshop. The i

Answer 1

You could change the alpha of your border based on the background color of the view.

var r:Float!
var g:Float!
var b:Float!
var a:Float!

if self.view.backgroundColor.getRed(red:r, green:g, blue:b, alpha:a) {
  var imgv = UIImageView(frame: CGRect(x:100, y:100, width:100, height:100))
  imgv.image = UIImage(named:"name")
  imgv.layer.borderWidth = 2.0
  imgv.layer.borderColor = UIColor(red:r, green:g, blue:b, alpha:0.5).CGColor
  imgv.layer.cornerRadius = imgv.frame.size.width / 2
  imgv.clipsToBounds = true
}else{
   //Could not get the RGB of background color
}

You may see errors in this code because I have not yet tested it.

Answer 2

Assuming that you have alpha channel (like on photo with transparent background) it seems that regular convultion blur matrix should satisfy you.

However instead of going through RGB channels - you should go through ALPHA channel only.

Check the blur filter here: https://en.wikipedia.org/wiki/Kernel_%28image_processing%29

You are interested in box blur/gaussian blur. However to make this effect more smooth - you should use matrix of bigger size.

The reason that algorithm will satisfy your needs is that if all surrounding pixels have alpha 0 - it will be still 0. If 255 - it will stay 255. Just pixels in area of border between alpha 0/255 will be affected.

Edit:

Please check this fiddle with chrome (in ff that's really slow): http://jsfiddle.net/5L40ms65/

You can take a look into algorithm in the end of code. Since implementation i noted that: - no need to blur if all neigbour pixels are 255 or 0 (alpha channel) - it is required to blur also RGB in other case

In general:

RADIUS = 2 (makes total width of matrix = 5)
For x = 0..width
  for y = 0..width
    if all pixels in square of radius 2 are alpha = 0
      do nothing
    elsif all pixels in square have alpha = 255
      do nothing
    else
      pixel[x][y].RGB = average RGB of adjacent pixels where alpha != 0
      pixel[x][y].ALPHA = average ALPHA in square

Example result with radius=2

Of course this is rather concept program, there is a lot of place for memoization and tuning this script however it should make a big picture clear