有没有一种简单的方法可以减少 IndexedColorModel 中的颜色数量?
我有一个大的 8 位 PNG 图像.我正在使用 Java 将图像切成较小的 32x32 图像.我使用 Java 的 ImageIO 将 PNG 加载到 BufferedImage 中，然后将其称为 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.
问题是生成的图像与原始图像具有相同的 IndexColorModel.例如，一个 32x32 的图块总共只有 8 种颜色，但它包含一个颜色模型，其中包含来自原始图像的所有 100 多种颜色.
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.
我想在写出 PNG 之前从 32x32 磁贴的 IndexColorModel 中删除未使用的颜色.包含图像中未使用的颜色的颜色数据是没有意义的，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.
是否有内置机制可以做到这一点，或者有人可以指出一种(简单的)方法来修改/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！
看看java.awt.image中的ColorConvertOp.
Take a look at ColorConvertOp in java.awt.image.
基本上，您创建所需深度的新 IndexColorModel.如果你真的想要最小的，你可以遍历 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 创建一个 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.