#16 Ability to set jpeg quality of ppmtoy4m output.

closed
None
5
2005-12-25
2005-12-25
J CMD
No

The man page for ppmtoy4m does not list any options to
adjust the quality setting (quantization level) for the
output.

For example, here is the command I am using from
qdvdauthor to generate the menu:

jpegtopnm "/tmp/Hanne/Main Menu VMGM/background.jpg" |
ppmtoy4m -n 1 -F25:1 -A59:54 -I t -L -S 420mpeg2 |
mpeg2enc -b 8000 -f 8 -n p -o "/tmp/Hanne/Main Menu
VMGM/menu.m2v"

The file "/tmp/Hanne/Main Menu VMGM/background.jpg" is
perfect to the nakede eye and mpeg2enc lets me set the
bitrate to be DVD quality, but the quality is still
degraded to the point that the readibility of the text
is reduced, apparently because the default quality
level of ppmtoy4m is set fairly low; and there is no
option to increase it.

The ability to specify a higher jpeg quality for the
output of ppmtoy4m would be useful.

Discussion

  • Bernhard Praschinger

    • assigned_to: nobody --> waldviertler
    • status: open --> closed
     
  • Bernhard Praschinger

    Logged In: YES
    user_id=155293

    2 Notes PPM and y4m are not compressed formates. So there is
    no need to set a quality. (Ever set the qualiy of a
    uncompressed BMP or TIFF ?)

    You loose some quality whne converting from jpeg->ppm and a
    littel when you convert to 420mpeg2. The main factor here is
    mpeg2enc.

    If you have a problem with the quality of the output take a
    look at the mjpeghowto. There are some hints how to get a
    better picture quality. You might also want to check out the
    mpeg2enc manpage. And read at least the decription of the -q
    option.

     
  • J CMD

    J CMD - 2005-12-25

    Logged In: YES
    user_id=1374990

    Thanks. I've used the -q option before, but increasing the
    quality in mpeg2enc didn't make a visible difference. The
    biggest improvement I managed to get was in dropping the
    "-l t" option, trying to interlace a single frame static
    menu seemed to just reduce the effective resolution.
    Perhaps I should suggest to the qdvdauthor that he should
    make the "-l p" option the default instead.

     

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