Decode Epson print (ESC-i) command decoding/encoding

Question

I'm trying to understand the algorithm used for compression value = 1 with the Epson ESCP2 print command, "ESC-i". I have a hex dump of a raw print file which looks, in part, like the hexdump below (note little-endian format issues).

000006a  1b  (  U 05 00 08 08 08 40 0b 
         units; (page1=08), (vt1=08), (hz1=08), (base2=40 0b=0xb40=2880)
...
00000c0 691b 0112 6802 0101 de00
        esc i 12 01 02 68 01 01 00
        print color1, compress1, bits1, bytes2, lines2, data...
          color1 = 0x12 = 18 = light cyan
          compress1 = 1
          bits1 (bits/pixel) = 0x2 = 2
          bytes2 is ??? = 0x0168 = 360
          lines2 is # lines to print = 0x0001 = 1
00000c9                       de 1200 9a05 6959
00000d0 5999 a565 5999 6566 5996 9695 655a fd56
00000e0 1f66 9a59 6656 6566 5996 9665 9659 6666
00000f0 6559 9999 9565 6695 9965 a665 6666 6969
0000100 5566 95fe 9919 6596 5996 5696 9666 665a
0000110 5956 6669 0456 1044 0041 4110 0040 8140
0000120 9000 0d00
                  1b0c 1b40 5228 0008 5200 4d45
                    FF esc @ esc ( R 00 REMOTE1

The difficulty I'm having is how to decode the data, starting at 00000c9, given 2 bits/pixel and the count of 360. It's my understanding this is some form of tiff or rle encoding, but I can't decode it in a way that makes sense. The output was produced by gutenprint plugin for GIMP.

Any help would be much appreciated.

In EPSON's ESC/P2 Reference Manual(page 222), ESC i is a 3-byte command for select immediate print mode. It's not the command you interpreted. If your interpretation makes sense, it's when vendors other than EPSON have extended their own commands. Please provide the printer vendor and model and their command specifications. — kunif
– kunif, Commented Mar 2, 2022 at 4:26
Thought I replied already; apparently not. The ESCP2 ref manual is obsolete. The command has been extended, and now takes more arguments: color (1 byte), compression type (1 byte), bits-per-dot (1 byte), bytes of uncompressed data (2 bytes, short int), number of lines (2 bytes, short int) — Gary Aitken
– Gary Aitken, Commented Mar 4, 2022 at 16:43
If so, please show where and how to get the latest specifications. Otherwise, only the EPSON support desk will be able to answer your question. If so, you probably don't need to ask questions on this site. — kunif
– kunif, Commented Mar 4, 2022 at 17:28
An updated version is not publicly available, as nearly as I have been able to determine. The one on their site is the 1997 version. — Gary Aitken
– Gary Aitken, Commented Mar 5, 2022 at 17:00
@kunif ESC i is immediate mode when outside graphics mode. When in graphics mode, it's interpreted differently -- it was repurposed by Epson. — Gábor
– Gábor, Commented May 17, 2023 at 17:09

Gary Aitken · Accepted Answer · 2022-03-02 22:48:45Z

The byte count is not a count of the bytes in the input stream; it is a count of the bytes in the input stream as expanded to an uncompressed form. So when expanded, there should be a total of 360 bytes. The input bytes are interpreted as either a count of bytes to follow, if positive, in which case the count is the byte value +1; and if negative the count is a count of the number of times the immediately following byte should be expanded, again, +1. The 0D at the end is a terminating carriage return for the line as a whole.

The input stream is only considered as a string of whole bytes, despite the fact that the individual pixel/nozzle controls are only 2 bits each. So it is not really possible to use a repeat count for something like a 3-nozzle sequence; a repeat count must always specify a full byte 4-nozzle combination.

The above example then specifies:

  0xde00  => repeat 0x00 35 times
  0x12    => use the next 19 bytes as is
  0xfd66  => repeat 0x66 4 times
  0x1f    => use the next 32 bytes as is
  etc.

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