Re: [Gimp-user] Epson <esc>i print format (Gutenprint question)

[Robert Krawitz <rlk alum mit edu>]

On 3/1/22 14:00, Gary Aitken wrote:
> On 3/1/22 8:59 AM, Gary Aitken wrote:
> > I have a simple image with one straight line of a single color.
> > Using the gutenprint dialog, I can print that file.
> > If I do a "reverse translation" of the raw file, there is one escp2 command
> > in it to print the line, shown below with some notes:
> >
> > 0000006a  1b  (  U 05 00 08 08 08 40 0b
> >          units; (page1=08), (vt1=08), (hz1=08), (base2= 40 0b = 0xb40 = 2880)
> > ...
> > 000000c0  1b  i 12 01 02 68 01 01 00
> >          Print color1, compress1, bits1, bytes2, lines2, data...
> >          color1 = 0x12 = 18 = light cyan
> >          compress1 = 1 (TIFF compression)
> >          bits1 (bits/pixel) = 0x2 = 2
> >          bytes2 = ???? = 0x068 = 360
> >          lines2 is # lines to print = 0x0001 = 1
> >          data = unknown, not dumped; specifies the dot size, 2 bits each
> > 00000124  0c
> >          FF
> >
> > What I don't understand is what bytes2 is counting.
> > There are 100 bytes between 000000c0 and 00000124.
> > What does the 360 mean?
> > Do the horizontal units factor or the compression type factor into this
> > in some way?
>
> My oversight, I see the bytes2 is a count of pixels in each line.
> But the question remains:
>
> > How do you compute where the next command (the FF) is?
>
> Do you have to actually decode the tiff data?

Yes you do.  It's basically a simple RLE compression scheme.  Repeated bytes (up to 128) are
represented as

[1-N][byte]

Non-repeated sequences (up to 128 bytes) are output as

[N][sequence]

It is possible for the "compression" to expand the data some; there's a very hairy calculation for
the worst case.