如何使用透明填充缩放Graphics2D图像 [英] How to scale a Graphics2D image with transparent padding

问题描述

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，并通过添加透明边框来缩放保持纵横比的图像左/右或上/下取决于图像。缩放工作正常，但对于我的生活，我无法使边框透明。

I'm trying to write a small method which takes a BufferedImage image and a new width and height and scales the image keeping the aspect ratio by adding transparent border to the left/right or top/bottom depending on the image. The scaling works fine but for the life of me I can't get the border to be transparent.

到目前为止，我有在pastebin.com上发布了以下代码，它可以很好地扩展。

So far I have the following code posted on pastebin.com which does the scaling well.

我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背景，有时是白色但它似乎永远不会透明。

I've read a lot of manuals and other SO questions to no avail. I've tried numerous permutations of fills, composite types, image types, etc.. Sometimes I get a blue background, sometimes white but it never seems to be transparent.

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才能拥有 Color.WHITE 背景是透明的和在旧的上面绘制旧图像？感谢您的帮助。

Any idea what Graphics2D call I need to make to have the Color.WHITE background be transparent and draw the old image over the new? Thanks for any help.

修改：

原来这个问题我当时正试图用JPEG图像生成透明色。 JPEG不支持透明度。 Duh。

It turned out that the problem I was having was that I was trying to generate a transparent color with a JPEG image. JPEGs do not support transparency. Duh.

推荐答案

我刚试了一下它的确有效。

I've just tried it out and it works.

只需将 Color.WHITE 替换为新颜色（0,0,0,0）和 img.getType（） with BufferedImage.TYPE_INT_ARGB 。

Just replace Color.WHITE with new Color(0, 0, 0, 0), and img.getType() with 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）

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