To-do list:

Author's tasks:

* Make the -i option work (once the library can support suppressing
  normal IDAT processing).

* MNG support?  (May mean an MNG library has to be written first...)
  MNG test images are at ftp://swrinde.nde.swri.edu/pub/mng/images. 
  Glenn adds:

Also you can make all the test images you want by capturing animated   
GIF ad banners and converting them with ImageMagick's "convert".  I've
made about 450 of them and haven't yet found one that wouldn't convert.
Can't post them though because they don't belong to me.  Use "-quality 90"
to get the best compression of typical GIF banners.

Blue-sky stuff:

Structured syntax for ICC profiles.  See <http://www.color.org/>.

The following is a plausible XML syntax.  Would it be an improvement?

<IHDR
   height={long}
   width={long}
   bitdepth={byte} 
   [using=color+palette+alpha]	# PNG color type information
   [interlace=none|adam7]	# Adam7 assumed if interlacing on
/>

<PLTE>
   [<rgb r={byte} g={byte} b={byte}/>|<rgb name={string}>]*
</PLTE>

<IDAT>
   {data}
</IDAT>

<gAMA gamma={float}/>

<cHRM
   white=({float},{float})      # White point x and y
   red=({float},{float})
   green=({float},{float})
   blue=({float},{float})
/>

<sRGB intent={byte}/>           # Colorimetry intent, range 0-3

<iCCP name={keyword}>           # International Color Consortium profile
   <pixels>{data}</pixels>               
</iCCP>

<sBIT
   red={byte}                   # Color images only
   blue={byte}                  # Color images only
   green={byte}                 # Color images only
   gray={byte}                  # Grayscale images only
   alpha={byte}                 # Images with alpha only
/>

<bKGD
   red={short}                  # Color images only
   blue={short}                 # Color images only
   green={short}                # Color images only
   gray={short}                 # Grayscale images only
   index={byte}                 # Paletted images only
/>

<hIST>
   {short} [, {short}]*         # Count must match palette size
</hIST>

<tRNS
   [gray={short}]               # Grayscale images only
   [red={short}]                # True-color images only
   [green={short}]              # True-color images only
   [blue={short}]               # True-color images only
/>

or

<tRNS>
   [{byte}]*                    # Paletted images only
</tRNS>

<pHYs
   xpixels={long}
   ypixels={long}
   [per meter]
/>

<tIME
   year={short}
   month={byte}
   day={byte}
   hour={byte}
   minute={byte}
   second={byte}
/>

<tEXt keyword={keyword}>        # Ordinary text chunk
  {data}
</tEXt>

<zTXt keyword={keyword}>        # Compressed text chunk
  {data}
</zTXt>

<iTXt                           # International UTF-8 keywo
  language={keyword}
  keyword={keyword}
  translated={keyword}          # Translation of the keyword
  [compressed=yes|no]		# Defaults to "no"
>{data}</iTXt>


<oFFs
  xoffset={slong}
  yoffset={slong} 
  [unit=pixels|micrometers]*
/>

<sPLT name={keyword} depth={byte}>
   [<rgbaf r={short}, g={short}, b={short}, a={short}, f={short}>]*
</sPLT>

<pCAL
   name={keyword}
   x0={slong}
   x1={slong}
   mapping linear|euler|exponential|hyperbolic
   unit={string}
   [parameters={string}] 
>

<sCAL
   unit=meter|radian
   width={string}
   height={string}
/>

<IMAGE>
   {data}
</IMAGE>

<gIFg
   disposal={byte}
   input={byte}
   delay={short}
/>

<gIFx
   identifier={string}                # Must be 8 characters
   code={string}>                     # Must be 3 characters
>{data}</gIFx>

<private name={string}>               # Private chunk declaration
   {data}
</private>

In data, remember we have to escape any '<' or  '&' characters. Or use a
CDATA marked section, then you only have to escape ]]> which is unlikely
(but possible) to occur.

An XML parser is required to halt on well formedness errors, deal with
entities, and so on.