My understanding is alpha and opacity are same just different range.
Opacity is 0.0 to 1.0
Alpha is 0 to 255
Jim or Kevin will be authority on this.
Jasper
> On Mar 16, 2014, at 5:55 AM, Tom Schindl <tom.schi...@bestsolution.at> wrote:
>
> Hi,
>
> Maybe I'm completely wrong but to me it looks like the opacity I get
> from Image.getPixelReader.getColor() is wrong.
>
> If not mistaken the relation between alpha and opacity is expressed with:
>
> opacity = (255 - alpha) / 255.0
>
> which means:
>
> opacity 0 => alpha 255
> opacity 1 => alpha 0
>
> Running the following programm on a gif
>
>> public class OpacityBug extends Application {
>>
>> @Override
>> public void start(Stage primaryStage) throws Exception {
>> Image image = new
>> Image(getClass().getResourceAsStream("methpri_obj.gif"));
>> int width = (int) image.getWidth();
>> int height = (int) image.getHeight();
>>
>> PixelReader reader = image.getPixelReader();
>> for (int x = width - 1; x >= 0; x--) {
>> for (int y = height - 1; y >= 0; y--) {
>> int argb = reader.getArgb(x, y);
>> int alphaArgb = (argb >> 24) & 0xFF;
>> Color color = reader.getColor(x, y);
>> double opacity = color.getOpacity();
>> System.err.println(x+","+y + " => alpha: " + alphaArgb + "
>> op: " + opacity + " op-alpha: " + opacityToAlpha(opacity) + " color: " +
>> color);
>> }
>> }
>> }
>>
>>
>> private static int opacityToAlpha(double opacity) {
>> return (int)Math.round((((opacity * 255.0) - 255) * -1));
>> }
>>
>> public static void main(String[] args) {
>> Application.launch(args);
>> }
>> }
>
> produces and output like:
> 15,15 => alpha: 0 op: 0.0 op-alpha: 255 color: 0x00000000
>
> which to my understanding is wrong. The argb value is correct (if
> compared to the image because the pixel at 15,15 is fully transparent)
> but then the the opacity should be 1.0 but is the opposite.
>
> Looking at the code in Image I see:
>> @Override
>> public Color getColor(int x, int y) {
>> int argb = getArgb(x, y);
>> int a = argb >>> 24;
>> int r = (argb >> 16) & 0xff;
>> int g = (argb >> 8) & 0xff;
>> int b = (argb ) & 0xff;
>> return Color.rgb(r, g, b, a / 255.0);
>> }
>
> which means that:
> a) my formula from the above is wrong
> b) or there's the bug because it should be
> return Color.rgb(r, g, b, (255 - a) / 255.0);
>
> May I also suggest to add get a
> - Color.argb(int r,int g,int b,int alpha)
> maybe it is just me but I'm so much more used to alpha than opacity that
> I always have to look it up when i need it.
>
> Tom
