How to draw a bitmap with transparency

Question

How to draw a bitmap with a given color set as transparent?
For example I want all white pixels to be transparent.

Manish Burman · Answer 1 · 2011-03-21T19:31:23.763

14

You need to set the Alpha value for the paint you're passing to the Bitmap.

http://developer.android.com/reference/android/graphics/Paint.html#setAlpha%28int%29

Values vary from 0-255

EDIT:

Paint p = new Paint();
//Set Blue Color
p.setColor(Color.WHITE);
//Set transparency roughly at 50%
p.setAlpha(125);

edited Mar 21 '11 at 19:31

answered Mar 20 '11 at 23:57

Manish Burman

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I don't get it. How can I set some color to be transparent if there is only one parameter? To choose a color I need at least three parameters. Could You write a short example how to display a bitmap on the surface view with a transparent white color? – Tomek Tarczynski Mar 21 '11 at 08:27
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I should've replied to this sooner but here goes. p.setColor(Color.White) sets the color of your bitmap to white. Transparency is controlled by one value - aplha which goes between 0 & 255. 0 is completely transparent, 255 is completely opaque - hence p.setAlpha(125) is somewhere in the middle. Does that clear things up? – Manish Burman Aug 02 '11 at 12:51
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This just sets the entire bitmap to be semi-transparent it does not give the intended effect. – Brian Griffey Nov 27 '12 at 20:54
Yeah, I didn't realize that the op wanted to make only one color transparent without affecting the other colors in the bitmap. I misunderstood what he was asking for. Sorry! – Manish Burman Nov 28 '12 at 01:59
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Oddly enough, while this answer failed to answer the OP's question, it did answer the one I googled for. :) Thanks Manish! – William T. Mallard Aug 31 '13 at 18:47

score 4 · Accepted Answer · edited May 23 '17 at 12:18

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you need to check every pixel of image and change its color. you will get your answer in this Post

edited May 23 '17 at 12:18

Community

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answered Mar 21 '11 at 11:48

Saurabh Pareek

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This is the fastest way? I'm a bit shocked that there is no built-in function for that... – Tomek Tarczynski Mar 21 '11 at 12:28

score 1 · Answer 3 · answered Sep 14 '14 at 09:56

Another approach is drawing in trasparent color on your canvas (drawing holes). The bitmapu needs alpha channel.

    //Set transparent paint - you need all of these three
    Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
    paint.setXfermode(new PorterDuffXfermode(Mode.SRC_OUT));
    paint.setColor(Color.TRANSPARENT);

    // Do you wanna soften?
    // Set paint transparency:
    // 0 = transparent ink, no visible effect
    // 255 = full ink, hole in the bitmap
    p.setAlpha(192);

    // Do you want some blur?
    // Set blur radius in pixel
    paint.setMaskFilter(new BlurMaskFilter(10, Blur.NORMAL));

How to draw a bitmap with transparency

3 Answers3