Re: rendering png without page

[Carl Sorensen]

On 7/19/11 10:21 AM, "Federico Bruni" <address@hidden> wrote:

> 2011/7/19 Neil Puttock <address@hidden>
>> On 19 July 2011 16:08, Federico Bruni <address@hidden> wrote:
>> 
>>>> About the transparency in PNG, last year Patrick McCarty said that he could
>>>> implement it eventually:
>>>> http://lists.gnu.org/archive/html/lilypond-user/2010-04/msg00115.html
>>>> 
>>>> But AFAIK nobody sent a feature request to bug-lilypond (I can't find
>>>> anything in the tracker).
>> 
>> Probably because it's already implemented:
>> 
>> -dpixmap-format=pngalpha
>> 
>> 
> 
> Great!
> 
> But it's not documented... or I'm missing something? (I did a quick search)
> 
lilypond -dhelp

shows all the -d options.  (And this is documented in Usage 1.2 Command line
options for lilypond.)

When done, you get

  pixmap-format ("png16m")
                              Set GhostScript's output format for pixel
images.


This tells you that you need to go to GhostScript's output formats to get
the answer.

gs --help

displays all the devices for GhostScript, and includes the following (among
others):

  pkm pkmraw pksm pksmraw plan9bm png16 png16 png16m png16m png256 png256
   png48 pngalpha pngalpha pnggray pnggray pngmono pngmono pnm pnmraw ppm
 
A google search for ghostcript devices gets me

http://www.ghostscript.com/doc/current/Devices.htm#PNG

where I read:

PNG file format
PNG (pronounced 'ping') stands for Portable Network Graphics, and is the
recommended format for high-quality images. It supports full quality color
and transparency, offers excellent lossless compression of the image data,
and is widely supported. Please see the PNG website
<http://www.libpng.org/pub/png/pngintro.html> for a complete description of
the format.

Ghostscript provides a variety of devices for PNG output varying by bit
depth. For normal use we recommend png16m for 24-bit RGB color,
or pnggray for grayscale. The png256, png16 and pngmono devices respectively
provide 8-bit color, 4-bit color and black-and-white for special needs.

The pngalpha device is 32-bit RGBA color with transparency indicating pixel
coverage. The background is transparent unless it has been explicitly
filled. PDF 1.4 transparent files do not give a transparent background with
this device. Text and graphics anti-aliasing are enabled by default.


This is not directly documented in LilyPond, because it's not a feature of
LilyPond, it's a feature of GhostScript.

Thanks,

Carl