iText binary transparency bug - itext

Question

I came accross the following problem embedding a transparent java.awt.Image into a pdf with iText (tried with 2.1.7 und 5.5.9).
I suppose iText does not handle binary transparent images correctly in this special case when converting them from ARGB Image to iText Image.
When the Image provided only contains 100% and 0% transparent pixels (i.e. binary transparency), and all the pixels are black (the opaqe and transparent ones - i.e. all pixel of the image have color=black but alpha value of 0% or 100%), the transparent pixel color value is internally detected as beeing black (this is wrong in my opinion), which leads to an invisble image in the generated pdf.
Test-Case:
import java.awt.AlphaComposite;
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import com.itextpdf.text.BadElementException;
import com.itextpdf.text.Document;
import com.itextpdf.text.DocumentException;
import com.itextpdf.text.Image;
import com.itextpdf.text.PageSize;
import com.itextpdf.text.Paragraph;
import com.itextpdf.text.pdf.PdfContentByte;
import com.itextpdf.text.pdf.PdfWriter;
public class BinaryTransparencyBug {
private static Image bkgnd;
public static void main(String[] args) throws Exception {
bkgnd = Image.getInstance(new URL("http://gitlab.itextsupport.com/itext/sandbox/raw/master/resources/images/berlin2013.jpg"));
bkgnd.scaleAbsolute(PageSize.A4);
bkgnd.setAbsolutePosition(0, 0);
Document document = new Document();
File file = new File("target/binary_transparency_bug.pdf");
FileOutputStream outputStream = new FileOutputStream(file);
PdfWriter writer = PdfWriter.getInstance(document, outputStream);
document.open();
addBackground(writer);
document.add(new Paragraph("Binary transparency bug test case"));
document.add(new Paragraph("OK: Visible image (opaque pixels are red, non opaque pixels are black)"));
document.add(com.itextpdf.text.Image.getInstance(createBinaryTransparentAWTImage(Color.red,false,null), null));
document.newPage();
addBackground(writer);
document.add(new Paragraph("Suspected bug: invisible image (both opaque an non opaque pixels have the same color)"));
document.add(com.itextpdf.text.Image.getInstance(createBinaryTransparentAWTImage(Color.black,false,null), null));
document.newPage();
addBackground(writer);
document.add(new Paragraph("Analysis: Aliasing makes the problem disappear, because this way the image is not binary transparent any more"));
document.add(com.itextpdf.text.Image.getInstance(createBinaryTransparentAWTImage(Color.black,true,null), null));
document.newPage();
addBackground(writer);
document.add(new Paragraph("Analysis: Setting the color of the transparent pixels to anything but black makes the problem go away, too"));
document.add(com.itextpdf.text.Image.getInstance(createBinaryTransparentAWTImage(Color.black,false,Color.red), null));
document.close();
}
private static void addBackground(PdfWriter writer)
throws BadElementException, MalformedURLException, IOException, DocumentException {
PdfContentByte canvas = writer.getDirectContentUnder();
canvas.saveState();
canvas.addImage(bkgnd);
canvas.restoreState();
}
// Create an ARGB AWT Image that has only 100% transparent and 0%
// transparent pixels.
// All 100% opaque pixels have the provided color "color"
// All transparent pixels have the Color "backgroundColor"
public static BufferedImage createBinaryTransparentAWTImage(Color color, boolean alias, Color backgroundColor) {
Dimension size = new Dimension(200, 200);
BufferedImage awtimg = new BufferedImage(size.width, size.height, BufferedImage.TYPE_INT_ARGB);
Graphics2D g2d = awtimg.createGraphics();
if (backgroundColor!=null)
{
//Usually it doen't make much sense to set the color of transparent pixels...
//but in this case it changes the behavior of com.itextpdf.text.Image.getInstance fundamentally!
g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC, 0f));
g2d.setColor(backgroundColor);
g2d.fillRect(0, 0, size.width, size.height);
}
g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 1f));
g2d.setColor(color);
if (alias)
{
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
}
BasicStroke bs = new BasicStroke(2);
g2d.setStroke(bs);
for (int i = 0; i < 5; i++) {
g2d.drawLine((size.width + 2) / 4 * i, 0, (size.width + 2) / 4 * i, size.height - 1);
g2d.drawLine(0, (size.height + 2) / 4 * i, size.width - 1, (size.height + 2) / 4 * i);
}
return awtimg;
}
}

Answer 1

Here is my proposal for the fix of the problem:
in Image.getInstance(AWTImage,color,forcebw):
in the case forceBW=false and color=null:
for (int j = 0; j < size; j++) {
byte alpha = smask[j] = (byte) (pixels[j] >> 24 & 0xff);
/* bugfix by Chris Nokleberg */
if (!shades) {
if (alpha != 0 && alpha != -1) {
//as soon as there is any pixel with alpha not 0% or 100%
//switch to smask
shades = true;
} else if (transparency == null) {
//in binary transparency mode, determine the transparentPixel Color to be the
//value of the first Pixel we find with 100% transparency
if (alpha == 0) {
transparentPixel = pixels[j] & 0xffffff;
transparency = new int[6];
transparency[0] = transparency[1] = transparentPixel >> 16 & 0xff;
transparency[2] = transparency[3] = transparentPixel >> 8 & 0xff;
transparency[4] = transparency[5] = transparentPixel & 0xff;
// vvv--- added by mkl
// Check whether this value for transparent pixels
// has already been used for a non-transparent one
// before this position
for (int jj = 0; jj < j; jj++)
{
if ((pixels[jj] & 0xffffff) == transparentPixel)
{
// found a prior use of the transparentPixel color
// and, therefore, cannot make use of this color
// for transparency; we could still use an image
// mask but for simplicity let's use a soft mask
// which already is implemented here
shades = true;
break;
}
}
// ^^^--- added by mkl
}
} else if (((pixels[j] & 0xffffff) != transparentPixel) && (alpha==0)) {
//TB: The above if seems incorrect to me. (EDIT: it was if ((pixels[j] & 0xffffff) != transparentPixel)
//As soon as we find any pixel that has differnt color from
//transparentPixel-Color and alpha 0% or 100%
//switch of binary transparency mode.
//IMHO this should only be done if alpha==0!
//so the if clause should be
//((pixels[j] & 0xffffff) != transparentPixel) && (alpha==0)
shades = true;
}
//TB: Proposed fix:
else if ((pixels[j] & 0xffffff) == transparentPixel && alpha!=0) {
//switch of binary transparency mode, if we find any pixel with the transparentPixel-Color,
//but which is not transparent
shades = true;
}
}
...
}