Attached is a patch that allows a transparent pdf background to be retained if
an rgba image type is selected. Rather than switching on BufferedImage TYPE
constants, it appears the simplest solution is to just use fully transparent
white. Image types with alpha will get the expected transparent background
while others get white.
Does this make sense for inclusion into pdfbox?
Examples:
- convert to png image with rgba color -> image w/ transparent background (new)
- convert to png image with rgb color -> image w/ white background (as before)
- convert to png image with rgb color -> image w/ white background (as before)
- convert to jpg image with rgb image type -> image w/ white background (as
before)
...
Index: pdfbox/src/main/java/org/apache/pdfbox/pdmodel/PDPage.java
===================================================================
--- pdfbox/src/main/java/org/apache/pdfbox/pdmodel/PDPage.java (revision
945442)
+++ pdfbox/src/main/java/org/apache/pdfbox/pdmodel/PDPage.java (working copy)
@@ -69,7 +69,12 @@
private static final int DEFAULT_USER_SPACE_UNIT_DPI = 72;
private static final float MM_TO_UNITS =
1/(10*2.54f)*DEFAULT_USER_SPACE_UNIT_DPI;
-
+
+ /**
+ * Fully transparent that can fall back to white when image type has no
alpha.
+ */
+ private static final Color TRANSPARENT_WHITE = new Color( 255, 255, 255, 0
);
+
private COSDictionary page;
/**
@@ -706,7 +711,7 @@
BufferedImage retval = new BufferedImage( widthPx, heightPx, imageType
);
Graphics2D graphics = (Graphics2D)retval.getGraphics();
- graphics.setBackground( Color.WHITE );
+ graphics.setBackground( TRANSPARENT_WHITE );
graphics.clearRect( 0, 0, retval.getWidth(), retval.getHeight() );
graphics.scale( scaling, scaling );
PageDrawer drawer = new PageDrawer();
Thank you,
Armando
On May 17, 2010, at 3:30 PM, Armando Singer wrote:
> PDFToImage / PDFImageWriter seem to work very well for converting
> mainly text pdf documents to an image.
>
> However, my goal is to convert mainly text pdf documents into a png with
> multiple levels of alpha transparency and to retain the transparent
> background in the original PDF.
>
> It looks like the only thing preventing this is:
>
> graphics.setBackground( Color.WHITE );
>
> Inside PDPage convertToImage(int, int);
>
> I can get the desired result with:
>
> graphics.setBackground( new Color( 0, 0, 0, 0 ) );
>
> Questions:
>
> 1. Should the pdfbox default to a transparent background, at least if
> the chosen color mode is rgba? I'd rather not have to maintain a
> patch on the source!
>
> 2. Is there a better way to accomplish this? I'm not sure if just
> settign the background to transparent is the right thing to do in
> all cases, but it does acheive the desired result whent the pdf is
> just text (including antialiased parts with more than one bit of
> alpha).
>
> Thank you!
> Armando
>
