[FFmpeg-devel] [PATCH v3] avcodec/pngenc: support writing iCCP chunks

[Niklas Haas <ffmpeg@haasn.xyz>]

From: Niklas Haas <git@haasn.dev>

encode_zbuf is mostly a mirror image of decode_zbuf. Other than that,
the code is pretty straightforward. Special care needs to be taken to
avoid writing more than 79 characters of the profile description (the
maximum supported).

To write the (dynamically sized) deflate-encoded data, we allocate extra
space in the packet and use that directly as a scratch buffer. Modify
png_write_chunk slightly to allow pre-writing the chunk contents like
this. This implementation does unfortunately require initializing the
deflate instance twice, but deflateBound() is not redundant with
deflate() so we're not throwing away any significant work.

Also add a FATE transcode test to ensure that the ICC profile gets
encoded correctly.
---

Changes in v3:
- rewrite to write the chunk in-place (inside the packet buffer)

Actually, I implemented an AVBPrint-less version that I think I'm
happier with overall. The extent of the "crimes" needed to support
writing chunks in-place was a single `if` in png_write_chunk and
hard-coding an 8 byte start offset.

I like this the most, since it doesn't require dynamic allocation _at
all_. It also ends up producing a 1 byte smaller test file for some
reason (not as a result of any obvious bug, but simply because zlib
compresses the last few bytes of the stream in a slightly different way,
probably as a result of some internal heuristics related to the buffer
size - the decoded ICC profile checksum is the same).

---
 libavcodec/pngenc.c    | 93 +++++++++++++++++++++++++++++++++++++++++-
 tests/fate/image.mak   |  3 ++
 tests/ref/fate/png-icc |  8 ++++
 3 files changed, 102 insertions(+), 2 deletions(-)
 create mode 100644 tests/ref/fate/png-icc

diff --git a/libavcodec/pngenc.c b/libavcodec/pngenc.c
index 3ebcc1e571..e9bbe33adf 100644
--- a/libavcodec/pngenc.c
+++ b/libavcodec/pngenc.c
@@ -235,7 +235,8 @@ static void png_write_chunk(uint8_t **f, uint32_t tag,
     bytestream_put_be32(f, av_bswap32(tag));
     if (length > 0) {
         crc = av_crc(crc_table, crc, buf, length);
-        memcpy(*f, buf, length);
+        if (*f != buf)
+            memcpy(*f, buf, length);
         *f += length;
     }
     bytestream_put_be32(f, ~crc);
@@ -343,10 +344,88 @@ static int png_get_gama(enum AVColorTransferCharacteristic trc, uint8_t *buf)
     return 1;
 }
 
+static size_t zbuf_bound(const uint8_t *data, size_t size)
+{
+    z_stream zstream;
+    size_t bound;
+
+    zstream.zalloc = ff_png_zalloc,
+    zstream.zfree  = ff_png_zfree,
+    zstream.opaque = NULL;
+    if (deflateInit(&zstream, Z_DEFAULT_COMPRESSION) != Z_OK)
+        return 0;
+
+    zstream.next_in = data;
+    zstream.avail_in = size;
+    bound = deflateBound(&zstream, size);
+    deflateEnd(&zstream);
+    return bound;
+}
+
+static int encode_zbuf(uint8_t **buf, const uint8_t *buf_end,
+                       const uint8_t *data, size_t size)
+{
+    z_stream zstream;
+    int ret;
+
+    zstream.zalloc = ff_png_zalloc,
+    zstream.zfree  = ff_png_zfree,
+    zstream.opaque = NULL;
+    if (deflateInit(&zstream, Z_DEFAULT_COMPRESSION) != Z_OK)
+        return AVERROR_EXTERNAL;
+    zstream.next_in  = data;
+    zstream.avail_in = size;
+    zstream.next_out  = *buf;
+    zstream.avail_out = buf_end - *buf;
+    ret = deflate(&zstream, Z_FINISH);
+    deflateEnd(&zstream);
+    if (ret != Z_STREAM_END)
+        return AVERROR_EXTERNAL;
+
+    *buf = zstream.next_out;
+    return 0;
+}
+
+static int png_write_iccp(uint8_t **bytestream, const uint8_t *end,
+                          const AVFrameSideData *side_data)
+{
+    const AVDictionaryEntry *entry;
+    const char *name;
+    uint8_t *start, *buf;
+    int ret;
+
+    if (!side_data || !side_data->size)
+        return 0;
+
+    /* write the chunk contents first */
+    start = *bytestream + 8; /* make room for iCCP tag + length */
+    buf = start;
+
+    /* profile description */
+    entry = av_dict_get(side_data->metadata, "name", NULL, 0);
+    name = (entry && entry->value[0]) ? entry->value : "icc";
+    for (int i = 0;; i++) {
+        char c = (i == 79) ? 0 : name[i];
+        bytestream_put_byte(&buf, c);
+        if (!c)
+            break;
+    }
+
+    /* compression method and profile data */
+    bytestream_put_byte(&buf, 0);
+    if ((ret = encode_zbuf(&buf, end, side_data->data, side_data->size)))
+        return ret;
+
+    /* rewind to the start and write the chunk header/crc */
+    png_write_chunk(bytestream, MKTAG('i', 'C', 'C', 'P'), start, buf - start);
+    return 0;
+}
+
 static int encode_headers(AVCodecContext *avctx, const AVFrame *pict)
 {
     AVFrameSideData *side_data;
     PNGEncContext *s = avctx->priv_data;
+    int ret;
 
     /* write png header */
     AV_WB32(s->buf, avctx->width);
@@ -399,7 +478,14 @@ static int encode_headers(AVCodecContext *avctx, const AVFrame *pict)
     if (png_get_gama(pict->color_trc, s->buf))
         png_write_chunk(&s->bytestream, MKTAG('g', 'A', 'M', 'A'), s->buf, 4);
 
-    /* put the palette if needed */
+    side_data = av_frame_get_side_data(pict, AV_FRAME_DATA_ICC_PROFILE);
+    if ((ret = png_write_iccp(&s->bytestream, s->bytestream_end, side_data))) {
+        av_log(avctx, AV_LOG_WARNING, "Failed writing iCCP chunk: %s\n",
+               av_err2str(ret));
+        return ret;
+    }
+
+    /* put the palette if needed, must be after colorspace information */
     if (s->color_type == PNG_COLOR_TYPE_PALETTE) {
         int has_alpha, alpha, i;
         unsigned int v;
@@ -526,6 +612,7 @@ static int encode_png(AVCodecContext *avctx, AVPacket *pkt,
                       const AVFrame *pict, int *got_packet)
 {
     PNGEncContext *s = avctx->priv_data;
+    const AVFrameSideData *sd;
     int ret;
     int enc_row_size;
     size_t max_packet_size;
@@ -537,6 +624,8 @@ static int encode_png(AVCodecContext *avctx, AVPacket *pkt,
             enc_row_size +
             12 * (((int64_t)enc_row_size + IOBUF_SIZE - 1) / IOBUF_SIZE) // IDAT * ceil(enc_row_size / IOBUF_SIZE)
         );
+    if ((sd = av_frame_get_side_data(pict, AV_FRAME_DATA_ICC_PROFILE)))
+        max_packet_size += zbuf_bound(sd->data, sd->size);
     if (max_packet_size > INT_MAX)
         return AVERROR(ENOMEM);
     ret = ff_alloc_packet(avctx, pkt, max_packet_size);
diff --git a/tests/fate/image.mak b/tests/fate/image.mak
index 573d398915..da4f3709e9 100644
--- a/tests/fate/image.mak
+++ b/tests/fate/image.mak
@@ -385,6 +385,9 @@ FATE_PNG_PROBE += fate-png-side-data
 fate-png-side-data: CMD = run ffprobe$(PROGSSUF)$(EXESUF) -show_frames \
     -i $(TARGET_SAMPLES)/png1/lena-int_rgb24.png
 
+FATE_PNG_PROBE += fate-png-icc
+fate-png-icc: CMD = transcode png_pipe $(TARGET_SAMPLES)/png1/lena-int_rgb24.png image2 "-c png"
+
 FATE_PNG-$(call DEMDEC, IMAGE2, PNG) += $(FATE_PNG)
 FATE_PNG_PROBE-$(call DEMDEC, IMAGE2, PNG) += $(FATE_PNG_PROBE)
 FATE_IMAGE += $(FATE_PNG-yes)
diff --git a/tests/ref/fate/png-icc b/tests/ref/fate/png-icc
new file mode 100644
index 0000000000..fd92a9f949
--- /dev/null
+++ b/tests/ref/fate/png-icc
@@ -0,0 +1,8 @@
+a50d37a0e72bddea2fcbba6fb773e2a0 *tests/data/fate/png-icc.image2
+49397 tests/data/fate/png-icc.image2
+#tb 0: 1/25
+#media_type 0: video
+#codec_id 0: rawvideo
+#dimensions 0: 128x128
+#sar 0: 2835/2835
+0,          0,          0,        1,    49152, 0xe0013dee
-- 
2.35.1

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