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epochapex

epochapex

loadPixels() and PDF Exporter

in General Discussion • Other • 2 months ago

Hi there,

I'm working on a sketch and it needs to scan an image for colour values using loadPixels(). I'm trying to adjust it to export a PDF, but the PDF exporter doesn't like the loadPixels() function — it doesn't seem like it's included in the renderer.

Is there a work around?

I.E.

Is there a way to loadPixels (or similar function) in the PDF exporter?
Is there a way to export a PDF after loading pixels?
Or is there another solution?

Thanks for your help.

1

Replies(16)

PhiLho

PhiLho

Re: loadPixels() and PDF Exporter

2 months ago

Not too sure what you are trying to do exactly.
If you can reproduce your problem in a minimalistic sketch, it would be better.
I think you need to have a regular PGraphics where you can do your loadPixels(). Maybe as a copy of the PDF one.

dimkir

dimkir

Re: loadPixels() and PDF Exporter

2 months ago

Because of the nature of PDF format it uses vector graphics. (note that if you open typical PDF document, you can zoom as much as you want and you won't see any pixels on the lines or curves).

To put it in a very simple way: PDF is a text file which contains same commands you usually have in "draw()" except but they're in shorthand.

Eg. this text is fragment of PDF file which when rendered by PDF-reader looks like pic on the right

You can see that this PDF contains commands "Line" or "Point" or "Ellipse".

Basically you can say that PDF is just a sketch which only draws one frame (just like processing sketch with noLoop() ). Except that PDF-syntax is way less readable for humans than Processing.

So when in your sketch you do commands

void draw(){
line(...);
ellipse(...);
point(...);
}

when you use default renderer (JAVA2D) or (P2D), Processing actually updates pixels in the frameBuffer, however when you execute the same commands with (PDF) renderer all they do is just write text like:

\Line(...)
\Ellipse(...)(...)
\Point(...)

to text file with .pdf extension.

This is why loadPixels()/ updatePixels() is not supported, because there're NO pixels. It's just your sketch translated into another language (which is PostScript, see PDF PostScript langauge tutorial)

What may be solution to your problem (and that's what PhiLho has offered) is that you first work with pixels with your normal renderer (JAVA2D or P2D) and then when you' have drawn the visuals you want, you can createGraphics() with PDF. And write your stuff to the graphics. However if what you want is to copy many pixels to the PDF, I am not sure how well processing PDF renderer will work with so many individual pixels.

dimkir

dimkir

Re: loadPixels() and PDF Exporter

2 months ago

hope this helps

epochapex

epochapex

Re: loadPixels() and PDF Exporter

2 months ago

Thanks for the very thorough explanation.

I see now that I have to study the createGraphics() function a bit more.

So, if I want to use the loadPixels() function and then draw vectors do I:

Specify the Java2D or P2D renderer in the parameter of the size() function? size(canvasWidth,canvasHeight, P2D); Or do I just leave it out?
And then specify the PDF renderer in the createGraphics parameter which would occur in the createGraphics() function? createGraphics(canvasWidth, canvasHeight, PDF, path);

Is Processing smart enough to switch renderers in the same sketch? (e.g. a separate one for a graphic buffer)

I appreciate your help — I don't think this has been answered on the forums yet. I'll share the answer for others on Twitter.

PhiLho

PhiLho

Re: loadPixels() and PDF Exporter

2 months ago

For some strange reason, Zoho marked the detailed answer as spam (finding a stupid pattern like 'cialis' in specialist or similar). I unmarked it so it is visible, and removed your answer where you quote it, epochapex.

And, yes, each PGraphics is a separate graphic buffer, independent of the others. You can do draw one buffer over the other, draw in parallel the same things, etc.
If you don't specify a renderer in the size() call, it is Java2D by default.

dimkir

dimkir

Re: loadPixels() and PDF Exporter

2 months ago

@PhiLho:

seems like zoho is marking all my posts as spam whenever I embed image from other website http://s21.postimg.org/9zppq709j/screenshot_8.png

@epochapex:

To understand PDF a bit better you may want to play around with simple examples from http://processing.org/reference/libraries/pdf/ until you're sure what every line does.

Also it seems that PDF Graphics impelementation in Processing doesn't really have any of the pixel methods ( loadPixels() and even get() see for yourselves. https://github.com/processing/processing/blob/544df088ca0ed6439811e5decb7fb0518085f17a/java/libraries/pdf/src/processing/pdf/PGraphicsPDF.java#L493

Also I tried to make an example of how to save contents of current sceen to PDF

And here's the example on github:

https://github.com/dimkir/processingForumSnippets/tree/scr2pdf/pdfWriter

PhiLho

PhiLho

Re: Re: loadPixels() and PDF Exporter

2 months ago

" seems like zoho is marking all my posts as spam whenever I embed image from other website"
Indeed, I found lot of your answers in the moderation area, all with an image. Stupid Zoho spam catcher...
I untagged them, they should be all visible from everybody, now.

epochapex

epochapex

Re: loadPixels() and PDF Exporter

2 months ago

PhilLho, Dimkir — Thanks so much for the clarification. I'll have a look at the examples. This is a great help.

epochapex

epochapex

Re: loadPixels() and PDF Exporter

2 months ago

Your sketch works, but from some reason I'm getting the following errors:

The method flushGraphicsToPdf(PGraphics,String) in the type sketchname is not applicable for the arguments (float,String)

dimkir

dimkir

Re: loadPixels() and PDF Exporter

2 months ago

It looks like when you're passing a "graphics" variabel to the flushGraphicsToPdf(THIS_VARIABLE_IS_NOT_GRAPHICS_BUT_FLOAT_VAR, ...)

epochapex

epochapex

Re: loadPixels() and PDF Exporter

2 months ago

Yes, that's where the problem is happening, but I'm not sure why. Maybe the graphics buffer is already in use.

I also notices that the PDF in your example is no actual vector information. It's a raster image embedded in the PDF.

What I'm trying to accomplish is saving vector data in a PDF. To this end, I found a processing library which can do this:

http://www.ricardmarxer.com/geomerative/

dimkir

dimkir

Re: loadPixels() and PDF Exporter

2 months ago

The most likely reason for a problem is because you defined somewhere yourself the variable which is pased to

flushGraphicsToPdf(THIS_ONE_SHOULD_BE_PGRAHICS_BUT_YOU_DECLARED_IT_AS_FLOAT_SOMEWHERE, ...)

As to

I also notices that the PDF in your example is no actual vector information. It's a raster image embedded in the PDF.

This is something which you were asking yourself:

I'm working on a sketch and it needs to scan an image for colour values using loadPixels()

you can only access pixels in raster image. They don't exist in vector formats.

Also if you want to write VECTOR information into PDF, you can uncomment these lines from the draw() method from this example: https://github.com/dimkir/processingForumSnippets/blob/master/pdfWriter/pdfWriter.pde#L44

pdfGraphics.fill(random(255));
pdfGraphics.stroke(random(255));
randomShape(pdfGraphics);

And then these lines will be writing vector information to file until you click mouse.

Hope this helps.

As to Geomerative library by Ricard Marxer this is an amazing library. And a must learn for every processing programmer.

epochapex

epochapex

Re: loadPixels() and PDF Exporter

2 months ago

Hi Dimkir,

Sorry for not explaining properly. What I'm doing is:

Loading an image and analyzing its pixels in a grid using loadPixels()
Generating an array of objects that contain the colour information from loadPixels()
Distributing them in a grid
Saving them (right now it's raster, but I'm trying to save vector)

Here's a final example of what my sketch is outputting:

http://www.flickr.com/photos/epochapex/sets/72157632547424502/

I'll try replacing the pdfGraphics() lines you've recommended. Although I feel at a loss to troubleshoot where I might be using the g variable to save the PDF. Maybe that graphics buffer is already occupied and needs to be cleared?

GoToLoop

GoToLoop

Re: loadPixels() and PDF Exporter

2 months ago

You can obtain a copy of g's PImage by issuing get().

epochapex

epochapex

Re: loadPixels() and PDF Exporter

2 months ago

Thanks GoToLoop. I'll try it. :)

epochapex

epochapex

Re: loadPixels() and PDF Exporter

2 months ago

Yay! I got it working. The PGraphics code was what it needed — no image buffer required in my case.

Thanks for your help people!

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