Trouble retaining transparent back color while setting opacity

[playwin2]

Hello,
I'm trying to set opacity of an image and also making it's back transparent....

The program suppose to mark the back color (the 1st pixel's color) of an image to transparent and also define the whole opacity (translucent) of the image...

The problem is if I, first make the image transparent and then apply the opacity the image is loosing it's backcolor :confused:

However if I do opposite that is , first apply opacity and then make it transparent then everythings is OK.

Why is this happening?

Bellow is the code that make the opacity...

private BufferedImage getTranslucentImage(float opacity)
    {
               
        int width = img.getWidth();
        int height = img.getHeight();


        BufferedImage tmp = new BufferedImage(width, height,
                BufferedImage.TRANSLUCENT);

        Graphics2D g2 = tmp.createGraphics();
        g2.setComposite(AlphaComposite.getInstance(
                AlphaComposite.SRC_OVER, opacity));
        g2.drawImage(img, null, 0, 0);
        g2.dispose();

        return tmp;
    }

[hardwired]

BufferedImage tmp = new BufferedImage(width, height,
        BufferedImage.TRANSLUCENT);

Translucent is a field of the Transparency interface which BufferedImage implements. Its value is 3.
The BufferedImage constructor you are using takes an int imageType. The types are listed in the Field Summary section of the BufferedImage api. The type whose value is 3 is TYPE_INT_ARGB_PRE. This may be what you want. Try experimenting with the types.

[playwin2]

Hello,

now I can preserve the back-color with transparency,

I just find and set the back color and then paint a rect (same size as the image) and then draw the image on it and then apply transparency, this preservs the back color with transparency.

However now I got problem to read them back in java ( I saved the image as png) , Does anyone know how to read TYPE_CUSTOM images in java?

[Supamagier]

You mean you have the problem that when you save an image Java does not read it's correct transparency?

In that case read the color per pixel and use this (which works for me):
Color c;

RED: (c>>>16)&0xff
GREEN: (c>>>8)&0xff
BLUE: c&0xff
ALPHA (tranparency): (c>>>24)&0xff

Hope this helps...

[playwin2]

No, I meant i can not preserve transparent backcolor when setting opacity , drawImage makes it black :mad:, if alpha is 0.

However presently I'm doing this and it seems working.... what do you think?

private BufferedImage getTranslucentPic(BufferedImage img, float opacity)
    {
        if( ! isBackTrans(img))
        {
            return setOpacity(img, opacity);
        }

        int width = img.getWidth();
        int height = img.getHeight();
        int oldBackColor = getBackColor(img);

        BufferedImage tmp = new BufferedImage(width, height,
                BufferedImage.TYPE_INT_ARGB);

        Graphics2D g2 = tmp.createGraphics();
        g2.setComposite(AlphaComposite.getInstance(
                AlphaComposite.SRC_OVER, opacity));
        g2.drawImage(img, null , 0, 0);
        g2.dispose();

        int newBackColor = tmp.getRGB(0, 0);

        for(int i = 0; i < height; i++)
        {
            for(int  j = 0; j < width; j++)
            {
                if( newBackColor == tmp.getRGB(j, i))
                {
                    tmp.setRGB(j, i, oldBackColor);
                }
            }
        }

        return tmp;
    }

    private BufferedImage setOpacity(
            BufferedImage img,
            float opacity)
    {
        int width = img.getWidth();
        int height = img.getHeight();

        BufferedImage tmp = new BufferedImage(width, height,
                BufferedImage.TYPE_INT_ARGB);
        Graphics2D g2 = tmp.createGraphics();
        g2.setComposite(AlphaComposite.getInstance(
                AlphaComposite.SRC_OVER, opacity));
        g2.drawImage(img, null, 0, 0);
        g2.dispose();

        return tmp;
    }