Well, docs indicate:
JPEG 2000 encoder
Required arguments
Infile (format pnm, pgm, ppm, pgx or bmp): -i Infile.pgm
And on those sites they say that PNM is PPM + PAM.
http://netpbm.sourceforge.net/doc/pnm.html
http://netpbm.sourceforge.net/doc/pam.html
From PAMS description:
"Transparent
Each of the visual image formats mentioned above has a variation that contains transparency information. In that variation, the tuple type has "_ALPHA" added to it (e.g. "RGB_ALPHA") and one more plane. The highest numbered plane is the opacity plane (sometimes called an alpha plane or transparency plane).
In this kind of image, the color represented by a pixel is actually a combination of an explcitly specified foreground color and a background color to be identified later."
Hope that helps.
JPEG 2000 encoder
Required arguments
Infile (format pnm, pgm, ppm, pgx or bmp): -i Infile.pgm
And on those sites they say that PNM is PPM + PAM.
http://netpbm.sourceforge.net/doc/pnm.html
http://netpbm.sourceforge.net/doc/pam.html
From PAMS description:
"Transparent
Each of the visual image formats mentioned above has a variation that contains transparency information. In that variation, the tuple type has "_ALPHA" added to it (e.g. "RGB_ALPHA") and one more plane. The highest numbered plane is the opacity plane (sometimes called an alpha plane or transparency plane).
In this kind of image, the color represented by a pixel is actually a combination of an explcitly specified foreground color and a background color to be identified later."
Hope that helps.