Transparent regions of a BufferedImage are writing out black

Question

I know this is something to do with compositing but I can't work out what. In an earlier section of code, a particular list of pixels in a BufferedImage are set to be transparent black:

        for(Pixel p : closed){
            Color c = new Color(image.getRGB(p.x, p.y));
            Color newC = new Color(0,0,0, 0);
            image.setRGB(p.x, p.y, newC.getRGB() & 0x00000000);
        }

        if(andCrop){
            image = image.getSubimage(left, top, right-left, bottom-top);
        }


        return image;

Then I attempt to write the image out:

try {

            BufferedImage out = new BufferedImage(image.getWidth(), image.getHeight(), java.awt.Transparency.TRANSLUCENT);
            Graphics2D g2d = out.createGraphics();
            g2d.setComposite(AlphaComposite.Clear);
            g2d.fillRect(0, 0, image.getWidth(), image.getHeight());
            g2d.setComposite(AlphaComposite.Src);
            g2d.drawImage(image, 0, 0, image.getWidth(), image.getHeight(), null);
            g2d.dispose();

            File outputfile = new File(file);
            ImageIO.write(out, "png", outputfile);
        } catch (IOException e) {

        }

Now, I know that 'out' is clear before I attempt to draw the image onto it. What I'm not getting is what's wrong with my compositing. Instead of coming out as transparent, I'm getting full-black.

All bufferedimages used are INT_ARGB.

EDIT - This has been solved. The image source was from ImageIO.read and the BufferedImage returned did not support alpha. A quick post-read conversion let the rest of the code run smoothly.

BTW - I would use [`BufferedImage.TYPE_INT_ARGB`](http://docs.oracle.com/javase/7/docs/api/constant-values.html#java.awt.image.BufferedImage.TYPE_INT_ARGB) for the image type rather than [`Transparency.TRANSLUCENT`](http://docs.oracle.com/javase/7/docs/api/constant-values.html#java.awt.Transparency.TRANSLUCENT). — Andrew Thompson, Dec 12 '12 at 01:47

score 1 · Answer 1 · 2012-12-12T02:21:05.170

1

Things that comes to my mind... (thanks to Andrew):

java.awt.Transparency.TRANSLUCENT = 3
TYPE_INT_ARGB = 2
TYPE_INT_ARGB_PRE = 3

public BufferedImage(int width,
                 int height,
                 int imageType)

Constructs a BufferedImage of one of the predefined image types. (TYPE_...)

http://docs.oracle.com/javase/1.4.2/docs/api/java/awt/image/BufferedImage.html

so it seems as basically it's a mixup.

Besides, what is the effect you want to achieve? you clear an empty image, then draw fully transparent pixels to it... I just don't get it.

edited Dec 12 '12 at 02:21

answered Dec 12 '12 at 02:07

I've used ARGB previously - translucent was after some desperate scrabbling. I thought perhaps the initial image needed to be transparent. – mtrc Dec 12 '12 at 02:17
My issues is that I have a BufferedImage which has some - but not all - transparent pixels. The border is transparent, for instance. I need to write it to a file, but when I do so, what were the transparent pixels come out opaque, not transparent. – mtrc Dec 12 '12 at 02:18
uh, there was a typo, in the source there is: public static final int OPAQUE = 1; public static final int BITMASK = 2; public static final int TRANSLUCENT = 3; - but the idea was that the value 3 (from TRANSLUCENT, here meaning just ARGB_PRE) is assigned in a bogus way – Dec 12 '12 at 02:22
Aha, thanks! That's good to know, just generally. I'll switch that back. – mtrc Dec 12 '12 at 02:42

score 0 · Accepted Answer · answered Dec 12 '12 at 02:19

Whelp, this has been downvoted now so I'm not sure this will be relevant, but the issue was that the original BufferedImage was being read in by ImageIO, and this image was not supporting ARGB. A quick post-read conversion allowed the rest of the code to work.

Transparent regions of a BufferedImage are writing out black

2 Answers2