在 Java 中调整索引图像的大小而不丢失透明度

Question

这是我调整图像大小的功能。质量虽然不是photoshop的，但也可以接受。

不可接受的是索引 png 上的行为。
我们预计，如果我们缩小具有透明索引的 256 色调色板的图像，我们将得到具有相同透明度的调整大小的图像，但事实并非如此。

因此，我们对新的 ARGB 图像进行了调整大小，然后将其减少到 256 种颜色。问题是如何“重新引入”透明像素索引。

private static BufferedImage internalResize(BufferedImage source, int destWidth, int destHeight) {
    int sourceWidth = source.getWidth();
    int sourceHeight = source.getHeight();
    double xScale = ((double) destWidth) / (double) sourceWidth;
    double yScale = ((double) destHeight) / (double) sourceHeight;
    Graphics2D g2d = null;

    BufferedImage resizedImage = new BufferedImage(destWidth, destHeight, BufferedImage.TRANSLUCENT);

    log.debug("resizing image to  w:" + destWidth + " h:" + destHeight);
    try {

        g2d = resizedImage.createGraphics();

        g2d.setRenderingHint(RenderingHints.KEY_ALPHA_INTERPOLATION, RenderingHints.VALUE_ALPHA_INTERPOLATION_QUALITY);
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2d.setRenderingHint(RenderingHints.KEY_COLOR_RENDERING, RenderingHints.VALUE_COLOR_RENDER_QUALITY);
        g2d.setRenderingHint(RenderingHints.KEY_DITHERING, RenderingHints.VALUE_DITHER_ENABLE);
        g2d.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BICUBIC);
        g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);

        AffineTransform at = AffineTransform.getScaleInstance(xScale, yScale);

        g2d.drawRenderedImage(source, at);

    } finally {
        if (g2d != null)
            g2d.dispose();
    }

//doesn't keep the transparency
    if (source.getType() == BufferedImage.TYPE_BYTE_INDEXED) {
        log.debug("reducing to color-indexed image");

        BufferedImage indexedImage = new BufferedImage(destWidth, destHeight, BufferedImage.TYPE_BYTE_INDEXED);

        try {
            Graphics g = indexedImage.createGraphics();
            g.drawImage(resizedImage, 0, 0, null);
        } finally {
            if (g != null)
                g.dispose();
        }
        System.err.println("source" + ((IndexColorModel) source.getColorModel()).getTransparentPixel()
                         + "   " + ((IndexColorModel) indexedImage.getColorModel()).getTransparentPixel());

        return indexedImage;
    }

    return resizedImage;

}

Answer 1

尝试改变

BufferedImage indexedImage = new BufferedImage(destWidth, destHeight, BufferedImage.TYPE_BYTE_INDEXED);

到

    BufferedImage indexedImage = new BufferedImage(destWidth, destHeight, BufferedImage.TYPE_BYTE_INDEXED, (IndexColorModel) source.getColorModel());

即使这对您没有帮助（如果调整大小，无论出于何种原因，改变了索引的特定颜色值，则可能不会有帮助），您可以使用给定的值创建新的事实BufferedImage可能IndexColorModel对您非常有用。

http://download.oracle.com/javase/6/docs/api/java/awt/image/BufferedImage.html#BufferedImage%28int,%20int,%20int,%20java.awt.image.IndexColorModel%29

编辑：刚刚注意到您的resizedImage构造函数可能应该使用BufferedImage.TYPE_INT_ARGB而不是BufferedImage.TRANSLUCENT. 不确定这是否会改变它的工作方式，但BufferedImage.TRANSLUCENT不应该传递给构造函数的那种形式。http://download.oracle.com/javase/1,5.0/docs/api/java/awt/image/BufferedImage.html#BufferedImage%28int,%20int,%20int%29

无论如何，也许尝试这样的事情：

DirectColorModel resizedModel = (DirectColorModel) resizedImage.getColorModel();
int numPixels = resizedImage.getWidth() * resizedImage.getHeight();

byte[numPixels] reds;
byte[numPixels] blues;
byte[numPixels] greens;
byte[numPixels] alphas;
int curIndex = 0;
int curPixel;

for (int i = 0; i < resizedImage.getWidth(); i++)
{
    for (int j = 0; j < resizedImage.getHeight(); j++)
    {
        curPixel = resizedImage.getRGB(i, j);
        reds[curIndex] = resizedModel.getRed(curPixel);
        blues[curIndex]= resizedModel.getBlue(curPixel);
        greens[curIndex] = resizedModel.getGreen(curPixel);
        alphas[curIndex] = resizedModel.getAlpha(curPixel);
        curIndex++;
    }
}

BufferedImage indexedImage = new BufferedImage(destWidth, destHeight, BufferedImage.TYPE_BYTE_INDEXED, new IndexColorModel(resizedModel.pixel_bits, numPixels, reds, blues, greens, alphas));

但不知道这是否真的有效。