问题描述
我有一个大的8位PNG图像。我使用Java将图像切割成较小的32x32图像。我使用Java的 ImageIO 将PNG加载到 BufferedImage 中，然后调用它的 getSubimage（x ，y，32,32）。然后我使用 ImageIO 将每个图块写成PNG。
I have a large 8-bit PNG image. I am using Java to slice the image into smaller 32x32 images. I use Java's ImageIO to load the PNG into a BufferedImage and then call it's getSubimage(x, y, 32, 32). I then use ImageIO to write each tile out as a PNG.
问题是生成的图像具有相同的 IndexColorModel 作为原始图像。例如，一个32x32磁贴只有8种颜色，但它包含一个颜色模型，其中包含原始图像中的所有100种颜色。
The problem is that the resulting image has the same IndexColorModel as the original image. For example, one 32x32 tile has only 8 total colors but it includes a color model with all 100-odd colors from the original image.
我想删除未使用的颜色在我写出PNG之前，从32x32 tile的 IndexColorModel 开始。没有任何意义，包括图像中未使用的颜色的颜色数据，我希望图像尽可能小。
I would like to remove unused colors from the 32x32 tile's IndexColorModel before I write out the PNG. There is no sense including color data for colors not used in the image and I'd like the images to be as small as possible.
是否有内置机制要做到这一点，还是有人能指点我（简单）修改/减少 ColorModel ？
Is there a built-in mechanism to do this or can someone point me to an (easy) way to modify/reduce the ColorModel?
谢谢！
推荐答案
在java.awt.image中查看 ColorConvertOp 。
Take a look at ColorConvertOp in java.awt.image.
基本上，您创建了所需深度的新 IndexColorModel 。如果你真的想要最小的，你可以走过 Raster 并计算颜色。否则，只需选择每像素4或5位。然后使用 TYPE_BYTE_BINARY 和 IndexColorMap 创建 BufferedImage 。最后，使用 ColorConvertOp 的 filter（）方法将原始数据复制到新的 BufferedImage 。
Basically, you create a new IndexColorModel of the desired depth. If you really want the smallest, you can walk through the Raster and count the colors. Otherwise, just choose 4 or 5 bits per pixel. Then create a BufferedImage with TYPE_BYTE_BINARY and the IndexColorMap. Finally, use the ColorConvertOp's filter() method to copy the original data to the new BufferedImage.
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