我可以检测 PNG 文件是否从多页 PDF 文件转换而来，并使用 ImageMagick 将图像拆分为单独的文件吗？

Question

我遇到一个问题，使用 OS X 的预览中的 PDF 导出功能创建的 PNG 文件在某些浏览器（Safari、Firefox）中显示为动画 GIF 或仅显示第一个页 (Chrome) 如果转换后的 PDF 文件不止一页（我所说的动画 GIF 是指它在不同页面之间闪烁）。有没有办法使用 PHP 来检测上传的 PNG 文件是否以这种方式转换，然后将其拆分为单独的图像并使用 ImageMagick 将它们拼接在一起？

Answer 1

它是动画 PNG 或 Mozilla APNG 格式文件。您可以像这样通过运行 pngcheck 检测它：

pngcheck -v npma33-png-convert-test.png

输出

File: npma33-png-convert-test.png (981954 bytes)
  chunk IHDR at offset 0x0000c, length 13
    1275 x 1650 image, 32-bit RGB+alpha, non-interlaced
  chunk acTL at offset 0x00025, length 8                   <--- APNG
    unknown private, ancillary, unsafe-to-copy chunk
  chunk iCCP at offset 0x00039, length 281
    profile name = ICC Profile, compression method = 0 (deflate)
    compressed profile = 268 bytes
  chunk pHYs at offset 0x0015e, length 9: 5906x5906 pixels/meter (150 dpi)
  chunk fcTL at offset 0x00173, length 26                  <--- APNG
    unknown private, ancillary, unsafe-to-copy chunk
  chunk IDAT at offset 0x00199, length 16384
    zlib: deflated, 32K window, superfast compression
  chunk IDAT at offset 0x041a5, length 16384
  chunk IDAT at offset 0x081b1, length 16384
  chunk IDAT at offset 0x0c1bd, length 16384
  chunk IDAT at offset 0x101c9, length 16384
  chunk IDAT at offset 0x141d5, length 16384
  chunk IDAT at offset 0x181e1, length 16384
  chunk IDAT at offset 0x1c1ed, length 16384
  chunk IDAT at offset 0x201f9, length 16384
  chunk IDAT at offset 0x24205, length 16384
  chunk IDAT at offset 0x28211, length 16384
  chunk IDAT at offset 0x2c21d, length 16384
  chunk IDAT at offset 0x30229, length 16384
  chunk IDAT at offset 0x34235, length 16384
  chunk IDAT at offset 0x38241, length 16384
  chunk IDAT at offset 0x3c24d, length 16384
  chunk IDAT at offset 0x40259, length 16384
  chunk IDAT at offset 0x44265, length 16384
  chunk IDAT at offset 0x48271, length 16384
  chunk IDAT at offset 0x4c27d, length 16384
  chunk IDAT at offset 0x50289, length 16384
  chunk IDAT at offset 0x54295, length 16384
  chunk IDAT at offset 0x582a1, length 16384
  chunk IDAT at offset 0x5c2ad, length 16384
  chunk IDAT at offset 0x602b9, length 16384
  chunk IDAT at offset 0x642c5, length 15969
  chunk fcTL at offset 0x68132, length 26                 <--- APNG
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0x68158, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0x6c168, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0x70178, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0x74188, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0x78198, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0x7c1a8, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0x801b8, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0x841c8, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0x881d8, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0x8c1e8, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0x901f8, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0x94208, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0x98218, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0x9c228, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xa0238, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xa4248, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xa8258, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xac268, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xb0278, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xb4288, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xb8298, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xbc2a8, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xc02b8, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xc42c8, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xc82d8, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xcc2e8, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xd02f8, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xd4308, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xd8318, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xdc328, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xe0338, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xe4348, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xe8358, length 16388
    unknown private, ancillary, unsafe-to-copy chunk
  chunk fdAT at offset 0xec368, length 14406
    unknown private, ancillary, unsafe-to-copy chunk
  chunk IEND at offset 0xefbba, length 0

它是 APNG 的赠品是 acTL 和 fcTL 块的存在，它们是 动画控制 和 帧控制.

您可以使用以下命令抑制这些块的输出（这将停止闪烁）：

convert npma33-png-convert-test.png -define png:exclude-chunk=acTL result.png

但我还没有对这是否会影响其他事情进行任何测试，例如实现的压缩或如何影响任何其他元数据 - 所以请自行检查。

所以，如果你使用 bash，你最终会得到这样的结果：

file="npma33-png-convert-test.png"
if pngcheck -v "$file" | grep -q acTL; then 
   convert "$file" -define png:exclude-chunk=acTL "$file"
fi

并排分离和重新加入帧的预期方式可能是

convert npma.... -separate +append result.png

或

convert npma... -coalesce +append result.png

但 ImageMagick 似乎也不愿意这样做 - 我只能猜测 APNG 并不真正受支持。

我也尝试过使用 Photoshop 风格 图层寻址，但这也不起作用：

convert npma...[0] page1.png
convert npma...[1] page2.png

我可以检测 PNG 文件是否从多页 PDF 文件转换而来，并使用 ImageMagick 将图像拆分为单独的文件吗？

Can I detect if a PNG file was converted from a multiple page PDF file and split the image into separate files using ImageMagick?

php

pdf

imagemagick