From b8f930fcb9f6960cc223f4a950b8f501d6ae39ff Mon Sep 17 00:00:00 2001 From: giraffedata Date: Sat, 12 Mar 2011 02:57:14 +0000 Subject: miscellaneous update git-svn-id: http://svn.code.sf.net/p/netpbm/code/userguide@1429 9d0c8265-081b-0410-96cb-a4ca84ce46f8 --- pngtopam.html | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 57 insertions(+) (limited to 'pngtopam.html') diff --git a/pngtopam.html b/pngtopam.html index a499ecb8..7fd04f00 100644 --- a/pngtopam.html +++ b/pngtopam.html @@ -20,6 +20,7 @@ pngtopam - convert a PNG image into a Netpbm image [-gamma=value] [-text=filename] [-time] +[-byrow] [pngfile]

Minimum unique abbreviation of option is acceptable. You may use double @@ -155,6 +156,62 @@ text comments or annotations.

Prints the tIME chunk to stderr. +
-byrow + +
This option can make pngtopam run faster or in environments +where it would otherwise fail. + +

pngtopam has two ways to do the conversion from PNG to PAM, using +respectively two facilities of the PNG library: + +

+ +
Whole Image + +
Decode the entire image into memory at once, using +png_read_image(), then convert to PAM and output row by row. + +
Row By Row +
Read, convert, and output one row at a time using png_read_row(). + +
+ +

Whole Image is generally preferable because the PNG library does more of +the work, which means it understands more of the PNG format possibilities now +and in the future. Also, if the PNG is interlaced, pngtopam does +not know how to assemble the rows in the right order. + +

Row By Row uses far less memory, which means with large images, it +can run in environments where Whole Image cannot and may also run +faster. And because Netpbm code does more of the work, it's possible +that it can be more flexible or at least give better diagnostic +information if there's something wrong with the PNG. + +

The Netpbm native code may do something correctly that the PNG library does +incorrectly, or vice versa. + +

In Netpbm, we stress function over performance, so by default +pngtopam uses Whole Image. You can select Row By Row with +-byrow if you want the speed or resource requirement improvement. + +

-byrow was new in Netpbm 10.54 (March 2010). + + +

-orientraw + +
A TIFF stream contains raster data which can be arranged in the +stream various ways. Most commonly, it is arranged by rows, with the +top row first, and the pixels left to right within each row, but many +other orientations are possible. + +

The common orientation is the same on the Netpbm formats use, so +tifftopnm can do its jobs quite efficiently when the TIFF raster +is oriented that way. + +

But if the TIFF raster is oriented any other way, it can take a +considerable amount of processing for tifftopnm to convert it to +Netpbm format. +

SEE ALSO

-- cgit 1.4.1