android - Converting ARGB to RGB in java -

i'm trying algorithms write method remove alpha value color , give identical rgb values seems test failing. belive called alpha blending? i'm not sure. algorithm use converting.

public static int removealpha(int foreground, int background) {         int redforeground = color.red(foreground);         int redbackground = color.red(background);         int greenforeground = color.green(foreground);         int greenbackground = color.green(background);         int blueforeground = color.blue(foreground);         int bluebackground = color.blue(background);         int alphaforeground = color.alpha(foreground);         int rednew = (redforeground * alphaforeground) + (redbackground * (1 - alphaforeground));         int greennew = (greenforeground * alphaforeground) + (greenbackground * (1 - alphaforeground));         int bluenew = (blueforeground * alphaforeground) + (bluebackground * (1 - alphaforeground));         return color.rgb(rednew, greennew, bluenew);     } 

and test this

@test     public void removealpha() {         int red = color.red;         assert.assertequals(0xffff7f7f, heatmap.removealpha(red, 0xffffffff));     }  junit.framework.assertionfailederror:  expected :-32897 actual   :-258 

when draw red in photoshop , set opacity 50%, gives me 255,127,127 rgb seems identical 50% opaque pure red. think there algorithm false. helps appreciated.

edit: here mock color:

 powermockito.mockstatic(color.class);         powermockito.when(color.rgb(mockito.anyint(), mockito.anyint(), mockito.anyint())).thenanswer(new answer<object>() {             @override             public object answer(invocationonmock invocation) throws throwable {                 int red = (int) invocation.getarguments()[0];                 int green = (int) invocation.getarguments()[1];                 int blue = (int) invocation.getarguments()[2];                 return (0xff << 24) | (red << 16) | (green << 8) | blue;             }         });         powermockito.when(color.alpha(mockito.anyint())).thenanswer(new answer<object>() {             @override             public object answer(invocationonmock invocation) throws throwable {                 return ((int)invocation.getarguments()[0])>>>24;             }         });         powermockito.when(color.red(mockito.anyint())).thenanswer(new answer<object>() {             @override             public object answer(invocationonmock invocation) throws throwable {                 return (((int)invocation.getarguments()[0])>>16) & 0xff;             }         });         powermockito.when(color.green(mockito.anyint())).thenanswer(new answer<object>() {             @override             public object answer(invocationonmock invocation) throws throwable {                 return (((int)invocation.getarguments()[0])>>8) & 0xff;             }         });         powermockito.when(color.blue(mockito.anyint())).thenanswer(new answer<object>() {             @override             public object answer(invocationonmock invocation) throws throwable {                 return (int)invocation.getarguments()[0] & 0xff;             }         }); 

note: i'm not java, can wrong. i'm using common programming notions, tweakings can needed.

i think messing data types... getting integer representation of color, i.e. 0-255, , multiplying if 0-1 representation. try this:

double alphaforeground = ((double)color.alpha(foreground)) / 255.0; int rednew = ((int)round((redforeground * alphaforeground) + (redbackground * (1 - alphaforeground)))); int greennew = ((int)round((greenforeground * alphaforeground) + (greenbackground * (1 - alphaforeground)))); int bluenew = ((int)round((blueforeground * alphaforeground) + (bluebackground * (1 - alphaforeground)))); 

there can rounding issues, but... should work.

just remark: color.red has 255 alpha channel. means removealpha(red, 0xffffffff) returns red itself, not 0xffff7f7f. in order value should write

int red = color.red; red.alpha = 0x80; 

(or close value)