如何在Java中生成透明GIF？ [英] How can I generate a transparent GIF in Java?

问题描述

以下代码生成半红半蓝的GIF图像。
如何获得半红半透明？

The code below generates a GIF image that’s half red and half blue. How can I get one that’s half red and half transparent?

我尝试过使用 IndexColorModel 构造函数，它将透明像素索引作为参数，并在调用 BufferedImage IMAGE_TYPE_ARGB c>构造函数，但没有什么对我有效。

I’ve tried using the IndexColorModel constructor that takes a transparent pixel index as a parameter, and also changing the image type to IMAGE_TYPE_ARGB in the call to the BufferedImage constructor, but nothing is working for me.

    int pixels[] = new int[90000];
    for (int x = 0; x < 300; x++) {
        for (int y = 0; y < 300; y++) {
            pixels[(300 * y) + x] = (x < y) ? 1 : 0;
        }
    }

    Color oneColor = Color.red;
    Color anotherColor = Color.blue;

    byte[] redMap = {(byte) (oneColor.getRed()), (byte) (anotherColor.getRed())};
    byte[] greenMap = {(byte) (oneColor.getGreen()), (byte) (anotherColor.getGreen())};
    byte[] blueMap = {(byte) (oneColor.getBlue()), (byte) (anotherColor.getBlue())};

    IndexColorModel colorModel = new IndexColorModel(1, 2, redMap, greenMap, blueMap);

    MemoryImageSource mis = new MemoryImageSource(300, 300, colorModel, pixels, 0, 300);

    Image image = Toolkit.getDefaultToolkit().createImage(mis);
    BufferedImage bufferedImage = new BufferedImage(300, 300, BufferedImage.TYPE_INT_RGB);
    bufferedImage.getGraphics().drawImage(image, 0, 0, null);

    try {
        ImageIO.write(bufferedImage, "gif", new File("example.gif"));
    } catch (IOException e) {
        e.printStackTrace();
    }

推荐答案

原来 BufferedImage.TYPE_BYTE_INDEXED 更适合这种情况。这段代码可以解决问题：

Turns out that BufferedImage.TYPE_BYTE_INDEXED is more appropriate for this case. This code does the trick:

    Color oneColor = Color.blue;
    Color anotherColor = Color.red;

    byte[] redMap = {(byte) (oneColor.getRed()), (byte) (anotherColor.getRed())};
    byte[] greenMap = {(byte) (oneColor.getGreen()), (byte) (anotherColor.getGreen())};
    byte[] blueMap = {(byte) (oneColor.getBlue()), (byte) (anotherColor.getBlue())};

    IndexColorModel colorModel = new IndexColorModel(1, 2, redMap, greenMap, blueMap, 0);

    int transparency = colorModel.getTransparency();
    int transparentPixel = colorModel.getTransparentPixel();
    System.out.println("colorModel.getTransparency(): " + transparency);
    System.out.println("colorModel.getTransparentPixel(): " + transparentPixel);

    BufferedImage bufferedImage = new BufferedImage(300, 300, BufferedImage.TYPE_BYTE_INDEXED, colorModel);

    WritableRaster writableRaster = bufferedImage.getRaster();

    for (int x = 0; x < 300; x++) {
        for (int y = 0; y < 300; y++) {
            int[] fill = new int[1]; // A large block...
            Arrays.fill(fill, (x < y) ? 0 : 1);  // ..  filled with one of the 7 first colors in the LUT.
            writableRaster.setSamples(x, y, 1, 1, 0, fill);
        }
    }

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