nbsp;scratchRows,
                     int&nbsp;bytesPerRow,
                     int&nbsp;bytesPerPixel)</pre>
<div class="block">Performs filtering on a row of an image.  This method may be
 overridden in order to provide a custom algorithm for choosing
 the filter type for a given row.

 <p> The method is supplied with the current and previous rows
 of the image.  For the first row of the image, or of an
 interlacing pass, the previous row array will be filled with
 zeros as required by the PNG specifica