How to remove constant background from an image?

Question

I'm not sure how to remove the paper background from this logo with v9.

This is really not the same as this question, but I think similar methods apply.

Answer 1

Not as classy as @belisarius', but:

i1 = Import@"http://i.stack.imgur.com/LKZfw.png"
ColorReplace[i1, RGBColor@PixelValue[i1, {2, 2}], .02]

Edit:

Perhaps it would be better would be to use Vitaliy's method, illustrated in this excellent answer. In this version, the image has a white background, not transparent (hence the difference in color, I suppose):

data = ImageData[i1];
Image[data /. {x_, y_, z_} /; 
    EuclideanDistance[{x, y, z}, data[[2, 2]]] < .3 -> {1, 1, 1}]

The value of .3 is taken from looking at a ListPlot of the EuclideanDistance values.

Answer 2

It's actually easier than your linked question, since your ROI is monochromatic!

i1 = Import@"http://i.stack.imgur.com/LKZfw.png"
i2 = Image[ImageData[
   ImageMultiply[Binarize[ColorSeparate[i1, "HSB"][[1]]], i1]] /. {0., 0., 0.} -> {1, 1, 1}]

Edit

If you want a fully saturated image, you could do something like

pmax = Position[ImageData[ColorSeparate[i1, "HSB"][[2]]], 1.][[1]]
Image@Replace[#, Except[{1., 1., 1.}] -> Extract[#, pmax], {2}] &@ ImageData[i2]