如何使用透明填充缩放Graphics2D图像-Java 学习之路

我正在尝试编写一个小方法，它采用 BufferedImage 图像和新的宽度和高度，并通过根据图像向左/右或上/下添加透明边框来缩放图像以保持纵横比 . 缩放工作正常，但对于我的生活，我不能让边框透明 .

到目前为止，我有following code posted on pastebin.com可以很好地进行缩放 .

我已经阅读了很多手册和其他SO问题无济于事 . 我尝试了很多填充，复合类型，图像类型等的排列 . 有时我得到一个蓝色的背景，有时是白色但它似乎永远不会透明 .

BufferedImage newImg = new BufferedImage(newWidth, newHeight, img.getType());
Graphics2D g = newImg.createGraphics();
g.setColor(Color.WHITE);
g.fillRect(0, 0, newWidth, newHeight);
g.drawImage(img, x, y, x + scaledWidth, y + scaledHeight, 0, 0,
    currentWidth, currentHeight, Color.WHITE, null);
g.dispose();
return newImg;

知道我需要做什么Graphics2D才能使 Color.WHITE 背景透明并在新的上面绘制旧图像？谢谢你的帮助 .

Edit:

事实证明，我遇到的问题是我试图用JPEG图像生成透明色 . JPEG不支持透明度 . 咄 .

4 回答

3
我刚试了一下它就可以了 .

只需将 Color.WHITE 替换为 new Color(0, 0, 0, 0) ，将 img.getType() 替换为 BufferedImage.TYPE_INT_ARGB .
```
BufferedImage img = ImageIO.read(new File("image.png"));
BufferedImage outImage = scaleWithPadding(img, 300, 100);
ImageIO.write(outImage, "png", new File("newImage.png"));
```
image.png: （204x53）

newImage.png: （300x100）
回复于 2024-04-30T08:26:57+08:00

我和你的帖子有相同的要求，how to make a color transparent上的这个页面给了我很多帮助 .

这是我的最终代码：

public BufferedImage getTransparentScaledImage(BufferedImage originalImage, int finalWidth, int finalHeight) {
    int originalWidth = originalImage.getWidth();
    int originalHeight = originalImage.getHeight();

    int newWidth;
    int newHeight;
    if (originalWidth == 0 || originalHeight == 0
            || (originalWidth == finalWidth && originalHeight == finalHeight)) {
        return originalImage;
    }

    double aspectRatio = (double) originalWidth / (double) originalHeight;
    double boundaryAspect = (double) finalWidth / (double) finalHeight;

    if (aspectRatio > boundaryAspect) {
        newWidth = finalWidth;
        newHeight = (int) Math.round(newWidth / aspectRatio);
    } else {
        newHeight = finalHeight;
        newWidth = (int) Math.round(aspectRatio * newHeight);
    }

    int xOffset = (finalWidth - newWidth) / 2;
    int yOffset = (finalHeight - newHeight) / 2;

    LoggerManager.getInstance().debug("frontoffice",
            "Image Servlet: [" + xOffset + "] [" + yOffset + "] [" + newWidth + "] [" + newHeight + "] [" + originalWidth + "] [" + originalHeight + "] [" + finalWidth + "] [" + finalHeight + "]");

    BufferedImage intermediateImage = new BufferedImage(finalWidth, finalHeight, BufferedImage.TYPE_INT_RGB);
    Graphics2D gi = intermediateImage.createGraphics();
    gi.setComposite(AlphaComposite.SrcOver);
    gi.setColor(Color.WHITE);
    gi.fillRect(0, 0, finalWidth, finalHeight);
    gi.drawImage(originalImage, xOffset, yOffset, xOffset + newWidth, yOffset + newHeight, 0, 0, originalWidth, originalHeight, Color.WHITE, null);
    gi.dispose();

    //if image from db already had a transparent background, it becomes black when drawing it onto another
    //even if we draw it onto a transparent image
    //so we set it to a specific color, in this case white
    //now we have to set that white background transparent
    Image intermediateWithTransparentPixels = makeColorTransparent(intermediateImage, Color.WHITE);

    //finalize the transparent image
    BufferedImage finalImage = new BufferedImage(finalWidth, finalHeight, BufferedImage.TYPE_INT_ARGB);
    Graphics2D gf = finalImage.createGraphics();
    gf.setComposite(AlphaComposite.SrcOver);
    gf.setColor(new Color(0, 0, 0, 0));
    gf.fillRect(0, 0, finalWidth, finalHeight);
    gf.drawImage(intermediateWithTransparentPixels, 0, 0, finalWidth, finalHeight, new Color(0, 0, 0, 0), null);
    gf.dispose();

    return finalImage;
}

public static Image makeColorTransparent(Image im, final Color color) {
    ImageFilter filter = new RGBImageFilter() {
        // the color we are looking for... Alpha bits are set to opaque
        public int markerRGB = color.getRGB() | 0xFF000000;

        public final int filterRGB(int x, int y, int rgb) {
            if ((rgb | 0xFF000000) == markerRGB) {
                // Mark the alpha bits as zero - transparent
                return 0x00FFFFFF & rgb;
            } else {
                // nothing to do
                return rgb;
            }
        }
    };

    ImageProducer ip = new FilteredImageSource(im.getSource(), filter);
    return Toolkit.getDefaultToolkit().createImage(ip);
}

回复于 2024-04-30T08:26:57+08:00

我实施了上述解决方案（或非常相似），如果你不使用，请注意

graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION,RenderingHints.VALUE_INTERPOLATION_BILINEAR);
graphics2D.setRenderingHint(RenderingHints.KEY_RENDERING,RenderingHints.VALUE_RENDER_QUALITY);
graphics2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON;

您的图像将以非常差的质量生成（由于缩放）

回复于 2024-04-30T08:26:57+08:00

0
您的原始 drawImage() 方法没有透明背景，因为正在使用背景颜色 . 替换为以下内容：
```
g.drawImage(img, x, y, x + scaledWidth, y + scaledHeight, 0, 0, currentWidth, currentHeight, null);
```
回复于 2024-04-30T08:26:57+08:00

如何使用透明填充缩放Graphics2D图像

4 回答

相关问题