On Fri, 8 Nov 2002, Rich wrote:
In article <d174dd4b87.d4b87d174d@bigpond.com>, pdeleeuw <pdeleeuw@telstra.com> writes:
OK I understand. I see where you are coming from. Would we use the fRAc chunk for this? We need to define a few standards before we go in too deep.
I'm not sure if the contents of the fRAc chunk were ever defined. Tim, can you comment on that?
You could always make an application-specific chunk. There is the possibility of chunk name clashes with other apps, so I think the libpng folks recommend registering chunks through them somehow. Its been a while since I looked at that, its probably in the libpng docs somewhere.
From http://www.libpng.org/pub/png/spec/pngext-1.2.0-pdg.html --8<------------
Chunks can be marked public and private. I think only the Public ones need to be run by them. 4. Chunks Not Described Here The definitions of some public chunks are being maintained by groups other than the core PNG group. In general, these are chunks that are useful to more than one application (and thus are not private chunks), but are considered too specialized to list in the core PNG documentation. 4.1. fRAc Fractal image parameters The fRAc chunk will describe the parameters used to generate a fractal image. The specification for the contents of the fRAc chunk is being developed by Tim Wegner, twegner@phoenix.net. In the future, chunks will be fully specified before they are registered. -------------- Also of Interes, this looks like it could be used to store the iteration counts and stuff.... 3.2. pCAL Calibration of pixel values When a PNG file is being used to store physical data other than color values, such as a two-dimensional temperature field, the pCAL chunk can be used to record the relationship (mapping) between stored pixel samples, original samples, and actual physical values. The pCAL data might be used to construct a reference color bar beside the image, or to extract the original physical data values from the file. It is not expected to affect the way the pixels are displayed. Another method should be used if the encoder wants the decoder to modify the sample values for display purposes. And I believe that Fractint currently stores it's info in a GIF Extention block, so as an interum solution until fRAc is defined is.. 3.5. gIFx GIF Application Extension The gIFx chunk is provided for backward compatibility with the GIF89a Application Extension. The Application Extension contains application-specific information. This chunk contains: [blah blah blah]