Question

我一直在尝试从APNG文件中提取所有png文件。我寻求帮助，而且没有太多帮助。我所能找到的只是一个开源库pngj，有了它我能够获得APNG文件的第一帧。

这是我正在使用的代码

public static void mirror(File orig, File dest, boolean overwrite)
         {
    PngReader pngr = FileHelper.createPngReader(orig);
    PngWriter pngw = FileHelper.createPngWriter(dest, pngr.imgInfo,
            overwrite);
    pngw.setFilterType(FilterType.FILTER_CYCLIC); // just to test all
                                                    // filters
    int copyPolicy = ChunkCopyBehaviour.COPY_ALL;
    pngw.copyChunksFirst(pngr, copyPolicy);
    ImageLine lout = new ImageLine(pngw.imgInfo);
    int cols = pngr.imgInfo.cols;
    int channels = pngr.imgInfo.channels;
    int[] line = new int[cols * channels];
    int aux;
    for (int row = 0; row < pngr.imgInfo.rows; row++) {
        ImageLine l1 = pngr.readRow(row);
        line = l1.unpack(line, false);
        for (int c1 = 0, c2 = cols - 1; c1 < c2; c1++, c2--) {
            for (int i = 0; i < channels; i++) {
                aux = line[c1 * channels + i];
                line[c1 * channels + i] = line[c2 * channels + i];
                line[c2 * channels + i] = aux;
            }
        }
        lout.pack(line, false);
        pngw.writeRow(lout, row);
    }
    pngr.end();
    pngw.copyChunksLast(pngr, copyPolicy);
    pngw.end();
    // // print unknown chunks, just for information
    List<PngChunk> u = ChunkHelper.filterList(pngr.getChunksList()
            .getChunks(), new ChunkPredicate() {
        public boolean match(PngChunk c) {
            return ChunkHelper.isUnknown(c);
        }
    });
    if (!u.isEmpty())
        System.out.println("Unknown chunks:" + u);
}

所以基本上我只是镜像一个apng文件，它被转换成一个png文件，这是第一帧。那么有人可以告诉我如何获取剩余的帧并将它们保存为png文件吗？任何帮助或提示都会被批评

Answer 1

实际上PNGJ库（我是作者）不支持APNG标准（题外话：我决定反对它，因为我不喜欢APGN方法，因为它不符合我的想法library：逐行加载“巨大”数据-IDAT-并直接在内存中加载块（元数据）; APGN通过将帧存储在块中来滥用PGN标准。）

你可以尝试使用它来做你想做的事情，但不能以优雅和健壮的方式。这是一个例子。除了丑陋之外，这不适用于部分帧（小于完整图像的帧，APNG支持的帧），也不适用于叠加层，~~或调色板图像（后期问题最容易修复）~~ （固定，希望）。

使用http://philip.html5.org/tests/apng/028.png

进行测试

import java.io.File;
import java.io.FileOutputStream;

import ar.com.hjg.pngj.FileHelper;
import ar.com.hjg.pngj.ImageLine;
import ar.com.hjg.pngj.PngHelperInternal;
import ar.com.hjg.pngj.PngReader;
import ar.com.hjg.pngj.PngWriter;
import ar.com.hjg.pngj.chunks.*;

public class ApngSplit {

    private static final String PREFIX = "apngf";

    /** reads a APNG file and tries to split it into its frames */
    public static void process(File orig) throws Exception {
        PngReader pngr = FileHelper.createPngReader(orig);
        File dest = new File(orig.getParent(), PREFIX + "0_" + orig.getName());
        PngWriter pngw = FileHelper.createPngWriter(dest, pngr.imgInfo, true);
        System.out.println("writing default frame " + pngw.getFilename());
        pngr.setChunkLoadBehaviour(ChunkLoadBehaviour.LOAD_CHUNK_ALWAYS);
        pngr.setMaxBytesMetadata(Integer.MAX_VALUE);
        pngr.setMaxTotalBytesRead(Long.MAX_VALUE);
        pngr.setSkipChunkIds(new String[] {});
        int copyPolicy = ChunkCopyBehaviour.COPY_PALETTE | ChunkCopyBehaviour.COPY_ALL_SAFE;
        pngw.copyChunksFirst(pngr, copyPolicy);
        int cols = pngr.imgInfo.cols;
        int channels = pngr.imgInfo.channels;
        for (int row = 0; row < pngr.imgInfo.rows; row++) {
            ImageLine l1 = pngr.readRow(row);
            pngw.writeRow(l1, row);
        }
        pngr.end();
        pngw.copyChunksLast(pngr, copyPolicy);
        pngw.end();
        processExtra2(orig, pngr.getChunksList());
    }

    private static void processExtra2(File orig, ChunksList chunks) throws Exception {
        int numframe = 0;
        FileOutputStream os = null;
        boolean afterIdat = false;
        for (PngChunk chunkApng : chunks.getChunks()) {
            if (chunkApng.id.equals("IDAT"))
                afterIdat = true;
            if (chunkApng.id.equals("fcTL") && afterIdat) {
                numframe++;
                if (os != null)
                    endPng(chunks, os);
                File dest = new File(orig.getParent(), PREFIX + numframe + "_" + orig.getName());
                System.out.println("writing seq " + numframe + " : " + dest);
                os = new FileOutputStream(dest);
                beginPng(chunks, os);
            }
            if (chunkApng.id.equals("fdAT")) {
                ChunkRaw crawf = chunkApng.createRawChunk();
                int seq = PngHelperInternal.readInt4fromBytes(crawf.data, 0);
                ChunkRaw crawi = new ChunkRaw(crawf.len - 4, ChunkHelper.b_IDAT, true);
                System.arraycopy(crawf.data, 4, crawi.data, 0, crawi.data.length);
                crawi.writeChunk(os);
            }
        }
        if (os != null)
            endPng(chunks, os);
    }

    private static void endPng(ChunksList chunks, FileOutputStream fos) throws Exception {
        chunks.getById1(PngChunkIEND.ID).createRawChunk().writeChunk(fos);
        fos.close();
    }

    private static void beginPng(ChunksList chunks, FileOutputStream fos) throws Exception {
        fos.write(new byte[] { -119, 80, 78, 71, 13, 10, 26, 10 }); // signature
        chunks.getById1(PngChunkIHDR.ID).createRawChunk().writeChunk(fos);
        PngChunk plte = chunks.getById1(PngChunkPLTE.ID);
        if (plte != null)
            plte.createRawChunk().writeChunk(fos);
    }

    public static void main(String[] args) throws Exception {
        process(new File("C:/temp/029.png"));
    }

}

Answer 2

可能会有所帮助的一些资源：

这些示例显示了如何读取apng文件，但它是C并使用libpng： https://sourceforge.net/projects/apng/files/libpng/examples/
这是一些Java代码，但它只能创建APNG文件，而不能读取它们： https://www.reto-hoehener.ch/japng/index.html
以下是用于读取和显示APNG文件的JavaScript代码： https://github.com/davidmz/apng-canvas

在java中从APNG中提取png文件

2 个答案: