Transparency and resolution problems with exported PDF

Core Library Questions

hmj6jmh

Transparency and resolution problems with exported PDF

in Core Library Questions • 9 months ago

I am trying to create a PDF with image content that has a transparent background. I have tried various methods with disappointing results.

I tried the direct-to-pdf beginRecord(PDF, "filename.pdf") method:

import processing.pdf.*;
void setup() {
size(580, 580);
noLoop();
beginRecord(PDF, "image_test_direct_pdf.pdf");
}
void draw() {
PImage img;
img = loadImage("moon.0096_cr.png");
imageMode(CENTER);
background(0);
pushMatrix();
translate(width/2, height/2);
image(img,0,0,width/4, height/4);
popMatrix();
endRecord();
}

This looks great and has 180ppi resolution but the transparency has been replaced with opaque gray.

The buffered pdf surface (PGraphicsPDF) createGraphics(width, height, PDF, "filename.pdf") method:

import processing.pdf.*;
PGraphicsPDF pg;
void setup() {
size(580, 580);
pg = (PGraphicsPDF) createGraphics(width, height, PDF, "image_test_pdf_createGraphics.pdf");
noLoop(); // Stops Processing from continuously executing the code within draw()
}
void draw() {
beginRecord(pg);
PImage img;
img = loadImage("moon.0096_cr.png");
imageMode(CENTER);
image(img, width/2, height/2);
pg.imageMode(CENTER);
pg.background(0);
pg.pushMatrix();
pg.translate(width/2, height/2);
pg.image(img,0,0,width/4, height/4);
pg.popMatrix();
endRecord();
}

Interestingly enough, this also looks just as good but Acrobat is showing only 72ppi. What's up with that?! Same situation with the transparency.

The off-screen buffer createGraphics(width, height) method:

import processing.pdf.*;
PGraphics pg;
void setup() {
size(580, 580);
pg = createGraphics(width, height);
noLoop(); // Stops Processing from continuously executing the code within draw()
}
void draw() {
pg.beginDraw();
PImage img;
img = loadImage("moon.0096_cr.png");
pg.imageMode(CENTER);
pg.background(0);
pushMatrix();
pg.translate(width/2, height/2);
pg.image(img,0,0,width/4, height/4);
popMatrix();
pg.endDraw();
image(pg,0,0);
pg.save("image_test_createGraphics.png");
beginRecord(PDF, "image_test_createGraphics.pdf");
image(pg, 0, 0);
endRecord();
}

Now transparency is being preserved but the resolution is unacceptable. Again it is showing as 72ppi and this time it looks it...

On the PDF Export library page it says

Images don't look great, mostly because of the difference of expectations in how a PDF should look (scalable and high res) versus what happens when image data is written to it at 72 dpi.

And yet in the first example above, image data was written at 180ppi. I don't know why 72ppi would be the default. It is ridiculously low even for a small-screen monitor. But for a PDF which will likely be printed, 300-1200 ppi is the norm. Why isn't this adjustable? Is there a hack that can make it adjustable?

The PDF version of the exported files is 1.4 (Acrobat 5.x), which supports an alpha channel. I even made a PDF of the same version with the original image and the background was transparent. This also should be programmable. Is there a hack for this?

So I don't know where to go from here. It's either horrible resolution or no transparencies. I can't proceed with either situation. Does anyone know a work-around that will give me high resolution AND transparency at the same time. I still need scalable vector graphics as well for text and graphics objects so a high-res image is not an option.

Replies(4)

PhiLho

Re: Transparency and resolution problems with exported PDF

9 months ago

Quick search:
http://www.processing.org/discourse/beta/num_1276207292.html
https://forum.processing.org/topic/how-to-export-sketches-with-transparency-for-high-resolution-printing
https://forum.processing.org/topic/transparent-image-in-pdf-file
http://processing.org/discourse/beta/num_1252603890.html
and so on...

No ready-made solution, alas, just that you are not the first to have this issue...

" I still need scalable vector graphics"
Maybe you can try SVG instead?

hmj6jmh

Re: Transparency and resolution problems with exported PDF

9 months ago

Yeah, I read all those unresolved old posts before I decided to start a new one. I was hoping that, by now, someone has come up with a hack or something. BTW I have tried both SVG libraries and they didn't work at all. I got many errors like other people.

You mentioned iText so I did some investigating. The pdf library is apparently a wrapper for iText. The itext.jar file is together with the pdf.jar file in C:\Program Files\Image\processing-2.0b7\modes\java\libraries\pdf\library\. I hacked together some java code to reproduce the same scenario using pure itext code.

import java.awt.Color;
import java.io.*;
import com.lowagie.text.*;
import com.lowagie.text.pdf.*;
public class imagesPDF
{
public static void main(String arg[])throws Exception
{
Rectangle pageRect = new Rectangle (580, 580);
pageRect.setBackgroundColor(new Color(0x00, 0x00, 0x00));
Document document = new Document(pageRect);
PdfWriter.getInstance(document,new FileOutputStream("imagePDF.pdf"));
document.open();
Image image = Image.getInstance ("moon.0096_cr.png");
int ppi = 180;
image.scalePercent(100*72/ppi);
//image.scaleAbsolute(document.getPageSize().getWidth()/4, document.getPageSize().getHeight()/4);
image.setAbsolutePosition(document.getPageSize().getWidth()/2 - image.getScaledWidth()/2, document.getPageSize().getHeight()/2 - image.getScaledHeight()/2);
document.add(image);
document.close();
}
}

The results are surprising and alarming.

The resolution is 180 ppi as in the first example above, BUT the transparency is honored, which is the DEFAULT for PNG in iText PDFs. Same PDF version of 1.4. The transparency shows up in preflight analysis. I don't know what the red X means other than some error, but it may not be good for the service provider. I don't know. But it looks great! I'm getting "high" resolution AND transparency. So now my question is, if this is the default behavior of iText, why isn't it being implemented in the library. I was careful to use the Processing itext.jar, in the directory listed above, directly, to level the playing field, so-to-speak. It is an older version. You will notice that I set the resolution directly with scalePercent so I would get exactly 180 ppi. image.scaleAbsolute(document.getPageSize().getWidth()/4, document.getPageSize().getHeight()/4) gave me like 178.749 ppi. :)

I know people have been able to incorporate calls to iText functions in their .PDE files but I don't know how to mix code like that. Maybe someone here does know and can give an example of how you could make a call to one of the image scale functions from my original script and put the image into the PDF using iText's image function.

PhiLho

Re: Transparency and resolution problems with exported PDF

9 months ago

" I have tried both SVG libraries"
Which ones?
Since I made one (a third one?), I am interested to have feedback.

" The transparency shows up in preflight analysis. I don't know what the red X means other than some error, but it may not be good for the service provider."
I didn't know Preflight, so I went to their site, and they warn:
" Although transparency is now a widely accepted functionality within most design and page layout applications many printing companies are still wary of PDF files containing transparency and like to give them specific attention to ensure they are processed and imaged correctly. "

I suppose you use transparency, not to print, but to load the PDF in some vector drawing application, so it should be OK.

The problem is that iText, like Batik and similar libraries, can work in two modes: the native library mode, like the one you used above in the pure Java program, and the Java2D mode, where the library overrides AWT's Graphics2D, thus transforming regular AWT drawing calls to drawing instructions for the targeted output.
The latter is great for developers that have already Java2D drawings, as they can just make a thin wrapper around the library and redirect the drawings to it. That's what I made with my P8gGraphicsSVG library, inspired by the way PGraphicsPDF is done: if you look at its source, you will find it is quite small!

The downside is that this Java2D mode offers less flexibility overall, and has some limitations.
One of them is handling of fonts (you have to give the path to the font file to be able to use it), another seems to be transparency handling...

If your third attempt is almost OK with only the resolution issue, you can try and draw on a much bigger PGraphics, no?

" I don't know why 72ppi would be the default. It is ridiculously low even for a small-screen monitor."
72 dpi was the standard resolution of CRT monitors not so long ago...
I think it is the default of iText, unless otherwise specified.

Perhaps you can take the PGraphicsPDF as a start, and hack it to get the intended result: make a library out of it (compile and put the .class file in a jar) or just add the .java file to you sketch. Thus, you can add anything you might need.

hmj6jmh

Re: Transparency and resolution problems with exported PDF

9 months ago

"I have tried both SVG libraries"

Which ones?

Since I made one (a third one?), I am interested to have feedback.

I tried prosvg and the PDE couldn’t find the library even though it was in the libraries folder with the other libraries. I tried P8gGraphicsSVG but none of the examples worked so I gave up. I don’t really want SVG output anyway.

"The transparency shows up in preflight analysis. I don't know what the red X means other than some error, but it may not be good for the service provider."

I didn't know Preflight, so I went to their site, and they warn:

"Although transparency is now a widely accepted functionality within most design and page layout applications many printing companies are still wary of PDF files containing transparency and like to give them specific attention to ensure they are processed and imaged correctly. "

I suppose you use transparency, not to print, but to load the PDF in some vector drawing application, so it should be OK.

I tried fixing the problem in Acrobat and all it did was flatten the image (removed the transparency) and changed the entire background to dark gray. Bogus. And this is probably what a service provider is going to do too. I read that Adobe has a 100-page treatise about transparency in PDFs so I guess it’s not as easy as you might imagine. I mentioned in my other post, about fonts, that I intend to send this to a service provider, or actually to a local (cheap) photo printer like Costco. Their prices are great but I don’t know about quality. In any case I want the PDF to be perfect because they will not provide any personal service or expertise, I’m sure.

The latter is great for developers that have already Java2D drawings, as they can just make a thin wrapper around the library and redirect the drawings to it. That's what I made with my P8gGraphicsSVG library, inspired by the way PGraphicsPDF is done: if you look at its source, you will find it is quite small!

The downside is that this Java2D mode offers less flexibility overall, and has some limitations.

One of them is handling of fonts (you have to give the path to the font file to be able to use it), another seems to be transparency handling...

I’ll take a look but that transparency limitation would kill it for me.

If your third attempt is almost OK with only the resolution issue, you can try and draw on a much bigger PGraphics, no?

Well yeah, but it is not optimal. I plan to add different scalable fonts and vector graphics so it seems a real pain to have to worry about scaling everything to fit the large bitmap. Maybe not but I’d really like to be able to add some code and get the full functionality of iText, which BTW is quite sophisticated. Update: it doesn't matter how big you make your buffer, it still only outputs to a 72 ppi PDF. I could find nothing on changing the ppi of a PDF, at least with Acrobat Pro.

"I don't know why 72ppi would be the default. It is ridiculously low even for a small-screen monitor."

72 dpi was the standard resolution of CRT monitors not so long ago...

I think it is the default of iText, unless otherwise specified.

Not so long ago? You mean 15-20 years is ‘not so long ago’? In terms of Moore’s law it is comparable to the Middle Ages of computing. Yes, iText defaults, sadly, to 72 ppi. That’s why they provide scaling functions, which are obviously being ignored by the PDF library.

Perhaps you can take the PGraphicsPDF as a start, and hack it to get the intended result: make a library out of it (compile and put the .class file in a jar) or just add the .java file to you sketch. Thus, you can add anything you might need.

That’s the last thing I want to do. I might as well use iText directly rather than hack the library. How would you add a java file to my sketch above and access the iText functions using data from Processing as much as possible? That would be very helpful. I can’t find enough about doing that online. I’m not an experienced java programmer, though I write various scripting code all the time and do have experience with C++. I am using eclipse for both Processing and iText, so that helps a lot.

Top Reply