In the interests of accuracy and completeness, I propose a new special-
purpose public chunk for the PNG standard.

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 Title:         The 'tIML' Time Chunk
 Date:          Wed 11 Jun 1997
 Author:        David R. Tribble
 email:         david.tribble@beasys.com,
                dtribble@flash.net
 Phone:         +1-972-738-6125, 16:00-00:00 UTC
                +1-972-964-1720, 01:00-05:00 UTC
 Address:       *******************

 Description:

 'tIML' - Long-precision image last-modification time

 The 'tIML' chunk gives the time that the image was last modified.
 It contains:

     Year:     2 bytes (complete, for example, 1995, not 95)
     Month:    1 byte (1-12)
     Day:      1 byte (1-31)
     Hour:     1 byte (0-23)
     Minute:   1 byte (0-59)
     Second:   1 byte (0-60)
     Nanosec:  4 bytes (0-999,999,999)

 Universal coordinated time (UTC, sometimes called GMT) should be used
 rather than local time.

 This is an ancillary, public, safe-to-copy chunk.  There can be only one
 of these chunks types in a given image, but the chunk is not required.
 This chunk has no ordering constraints.

 This chunk is similar to the 'tIME' chunk, but encodes the modification
 time of the image with a higher resolution, to the nearest nanosecond,
 rather than only to the nearest second.

 The 'tIML' chunk is intended for use as an automatically-applied time
 stamp that specifies the actual time that the image was modified.
 It is recommended that 'tIML' not be changed by PNG editors that do not
 change the image data.

 The 'tIML' chunk encodes the time to a high accuracy in order to support
 applications that are capable of creating many images per second and for
 applications that require a high degree of time accuracy (such as
 astronomical and atomic imaging systems).  If subsecond accuracy is not
 available on the system that creates the image, the 'Nanosec' field should
 be set to zero.

 Since accuracy to the nearest nanosecond is possible, many existing
 standards for time encoding can be accommodated.  For example, the SMPTE
 time frame format encodes time in the form "HHH:MM:SS:FF", where HHH is
 the hour (relative to an arbitrary starting point in the past), MM is the
 minute, SS is the second, and FF is the frame number.  Several SMPTE
 frame rates are allowed, reflecting the number of frames per second: 24,
 30, and 30 drop.  Converting these values into 'tIML' chunks is
 straightforward.

 If a PNG file contains both a 'tIME' and a 'tIML' chunk, the one that
 encodes the latest date and time should take precedence.  (A time chunk
 is considered to encode a date later than another if the numeric fields
 comprising it are greater than the field of the other chunk, comparing
 the 'Year' field first, the 'Month' field second, and so forth, and the
 'Nanosec' field last.)

 Using a 'tEXt' chunk to encode the same information as the 'tIML' chunk
 is possible, but no standard keyword or text format has been proposed to
 accomplish this so far.

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Thank you for your consideration of this proposal.