Standard PNGs don't support editing. Simplifying it a bit, they are just what you said they are: losslessly compressed bitmaps (vs JPGs, which employ lossy compression, or GIFs which are also bitmaps, but only support up to a 256 color palette).
Fireworks PNGs contain a special header and extra data that allows them to retain vector and layer information. But they are not standard PNGs.
Fireworks PNG files contain a second "chunk" of data that other applications can't read, which contains proprietary information about things like slicing, interactivity, and any Live Effects that may have been applied.
And finally, to address this:
What gives? Clearly there is way more to the .png format than just losslessly compressed bitmaps.
Yes, there is more to PNG than the standard. Extensions have been added to standard PNG that allow for animation, for example.
I thought .pngs were just bitmaps compressed losslessly using some special png algorithm.
Well, they basically are. The lossless compression algorithm is a simple prediction filter followed by the standad Lempel-Ziv compression. It supports several image depth/formats (RGB with/without alpha channel ; gray ; palette) and it also supports some standard meta information ("Chunks"). Among these metainformation there are things like pysical resolution (DPI), and, in the case of paletted images some transparent colors.
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标准 PNG 不支持编辑。稍微简化一下，它们就是您所说的：无损压缩位图（与 JPG 相比，JPG 采用有损压缩，或者 GIF 也是位图，但最多只支持 256 种调色板）。
Fireworks PNG 包含特殊的标头和额外数据，允许它们保留矢量和图层信息。但它们不是标准的 PNG。
Adobe 参考页面：
最后，解决这个问题：
是的，PNG 不仅仅是标准。例如，标准 PNG 中添加了允许动画的扩展。
Standard PNGs don't support editing. Simplifying it a bit, they are just what you said they are: losslessly compressed bitmaps (vs JPGs, which employ lossy compression, or GIFs which are also bitmaps, but only support up to a 256 color palette).
Fireworks PNGs contain a special header and extra data that allows them to retain vector and layer information. But they are not standard PNGs.
Adobe's reference page:
And finally, to address this:
Yes, there is more to PNG than the standard. Extensions have been added to standard PNG that allow for animation, for example.
嗯，他们基本上是。无损压缩算法是一个简单的预测滤波器，后跟标准 Lempel-Ziv 压缩。
它支持多种图像深度/格式（带/不带 alpha 通道的 RGB；灰色；调色板）
它还支持一些标准元信息（“Chunks”）。这些元信息包括物理分辨率 (DPI) 等，对于调色板图像，还有一些透明颜色。
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Well, they basically are. The lossless compression algorithm is a simple prediction filter followed by the standad Lempel-Ziv compression.
It supports several image depth/formats (RGB with/without alpha channel ; gray ; palette)
and it also supports some standard meta information ("Chunks"). Among these metainformation there are things like pysical resolution (DPI), and, in the case of paletted images some transparent colors.
The specification is open