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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 [<b>-gamma</b>=<i>value</i>] [<b>-text</b>=<i>filename</i>] [<b>-time</b>] +[<B>-byrow</B>] [<I>pngfile</I>] <P>Minimum unique abbreviation of option is acceptable. You may use double @@ -155,6 +156,62 @@ text comments or annotations. <DD>Prints the tIME chunk to stderr. +<DT><B>-byrow</B> + +<DD>This option can make <b>pngtopam</b> run faster or in environments +where it would otherwise fail. + +<P><B>pngtopam</B> has two ways to do the conversion from PNG to PAM, using +respectively two facilities of the PNG library: + +<DL> + +<DT>Whole Image + +<DD>Decode the entire image into memory at once, using +<b>png_read_image()</b>, then convert to PAM and output row by row. + +<DT>Row By Row +<DD>Read, convert, and output one row at a time using <b>png_read_row()</b>. + +</DL> + +<P>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, <b>pngtopam</b> does +not know how to assemble the rows in the right order. + +<P>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. + +<p>The Netpbm native code may do something correctly that the PNG library does +incorrectly, or vice versa. + +<P>In Netpbm, we stress function over performance, so by default +<B>pngtopam</B> uses Whole Image. You can select Row By Row with +<b>-byrow</b> if you want the speed or resource requirement improvement. + +<p><b>-byrow</b> was new in Netpbm 10.54 (March 2010). + + +<dt><b>-orientraw</b> + +<dd>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. + +<p>The common orientation is the same on the Netpbm formats use, so +<b>tifftopnm</b> can do its jobs quite efficiently when the TIFF raster +is oriented that way. + +<p>But if the TIFF raster is oriented any other way, it can take a +considerable amount of processing for <b>tifftopnm</b> to convert it to +Netpbm format. + </DL> <H2 id="seealso">SEE ALSO</H2> |