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From "Shaola Ren (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (PDFBOX-1915) Implement shading with Coons and tensor-product patch meshes
Date Tue, 03 Jun 2014 13:06:02 GMT

     [ https://issues.apache.org/jira/browse/PDFBOX-1915?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Shaola Ren updated PDFBOX-1915:

    Attachment: shading7.rar

1. rendering correct images: asy-coons-but-really-tensor7.pdf, asy-tensor7.pdf, TENSOR7.pdf

the common characters of these files are, each image has a single data object stream, color
space is DeviceRGB

2. rendering part of the whole file: McAfee-ShadingType7.pdf

this file is made of several shading type 2 image and 1 shading type 7 image, the shading
type 7 is not converted by the program

in a usual file the parameter sequence is like this:
10 0 obj
<</ShadingType 7
/BitsPerCoordinate 24
/BitsPerComponent 16
/BitsPerFlag 8/Length 121>>stream
 ... endstream 

in this file:
18 0 obj
/AntiAlias false
/BitsPerComponent 8
/BitsPerCoordinate 32
/BitsPerFlag 8
/ColorSpace /DeviceCMYK
/Decode [1500.39 1711.32 -2589.48 -2378.55 0.0 1.0 0.0 1.0 0.0 1.0
0.0 1.0]
/Filter /FlateDecode
/Length 64760
/ShadingType 7
stream ... endstream 

when "ShadingType 7" is not at the beginning, the software has problem to deal with the corresponding
data, the shading type 2 part has a similar situation, this may explain why the converted
image lost the red top bar and the correct color of the letters in the gray area

when testing this file, the program throws this message: "org.apache.pdfbox.util.PDFStreamEngine
processOperator INFO: unsupported/disabled operation: BDC"

3. with color problems: XYZsweep7.pdf

the color space of this file is "ColorSpace 9 0 R", I think what I did in the shading package
is right, there must be some problem in the interpretation of the ColorSpace.

when testing this file, the program throus this message: "org.apache.pdfbox.util.PDFStreamEngine
processOperator INFO: unsupported/disabled operation: i"

4. cannot get image: lamp_cairo7.pdf

an file combined by many shading type 7 data streams, the software cannot work correctly here

Now, shading type 7 and shading type 6 have some duplicated code, I will create several shared
classes to remove these duplicates.

> Implement shading with Coons and tensor-product patch meshes
> ------------------------------------------------------------
>                 Key: PDFBOX-1915
>                 URL: https://issues.apache.org/jira/browse/PDFBOX-1915
>             Project: PDFBox
>          Issue Type: Improvement
>          Components: Rendering
>    Affects Versions: 1.8.5, 1.8.6, 2.0.0
>            Reporter: Tilman Hausherr
>            Assignee: Shaola Ren
>              Labels: graphical, gsoc2014, java, math, shading
>             Fix For: 2.0.0
>         Attachments: CONICAL.pdf, GWG060_Shading_x1a.pdf, HSBWHEEL.pdf, McAfee-ShadingType7.pdf,
Shadingtype6week1.pdf, TENSOR.pdf, XYZsweep.pdf, asy-coons-but-really-tensor.pdf, asy-tensor-rainbow.pdf,
asy-tensor.pdf, coons-function.pdf, coons-function.ps, coons-nofunction-CMYK.pdf, coons-nofunction-CMYK.ps,
coons-nofunction-Duotone.pdf, coons-nofunction-Duotone.ps, coons-nofunction-Gray.pdf, coons-nofunction-Gray.ps,
coons-nofunction-RGB.pdf, coons-nofunction-RGB.ps, coons2-function.pdf, coons2-function.ps,
coons4-function.ps, eci_altona-test-suite-v2_technical_H.pdf, lamp_cairo.pdf, pass4FlagTest.rar,
patchCases.jpg, patchMap.jpg, shading6ContourTest.rar, shading6Done.rar, shading7.rar, tensor-nofunction-RGB.pdf,
tensor-nofunction-RGB.ps, updateshading6ContourTest.rar
> Of the seven shading methods described in the PDF specification, type 6 (Coons patch
meshes) and type 7 (Tensor-product patch meshes) haven't been implemented. I have done type
1, 4 and 5, but I don't know the math for type 6 and 7. My math days are decades away.
> Knowledge prerequisites: 
> - java, although you don't have to be a java ace, just feel confortable
> - math: you should know what "cubic Bézier curves", "Degenerate Bézier curves", "bilinear
interpolation", "tensor-product", "affine transform matrix" and "Bernstein polynomials" are,
or be able to learn it
> - maven (basic)
> - svn (basic)
> - an IDE like Netbeans or Eclipse or IntelliJ (basic)
> - ideally, you are either a math student who likes to program, or a computer science
student who is specializing in graphics.
> A first look at PDFBOX: try the command utility here:
> https://pdfbox.apache.org/commandline/#pdfToImage
> and use your favorite PDF, or the PDFs mentioned in PDFBOX-615, these have the shading
types that are already implemented.
> Some simple source code to convert to images:
> String filename = "blah.pdf";
> PDDocument document = PDDocument.loadNonSeq(new File(filename), null);
> List<PDPage> pdPages = document.getDocumentCatalog().getAllPages();
> int page = 0;
> for (PDPage pdPage : pdPages)
> {
> ++page;
> BufferedImage bim = RenderUtil.convertToImage(pdPage, BufferedImage.TYPE_BYTE_BINARY,
> ImageIO.write(bim, "png", new File(filename+page+".png"));
> }
> document.close();
> You are not starting from scratch. The implementation of type 4 and 5 shows you how to
read parameters from the PDF and set the graphics. You don't have to learn the complete PDF
spec, only 15 pages related to the two shading types, and 6 pages about shading in general.
The PDF specification is here:
> http://www.adobe.com/devnet/pdf/pdf_reference.html
> The tricky parts are:
> - decide whether a point(x,y) is inside or outside a patch
> - decide the color of a point within the patch
> To get an idea about the code, look at the classes GouraudTriangle, GouraudShadingContext,
Type4ShadingContext and Vertex here
> https://svn.apache.org/viewvc/pdfbox/trunk/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/graphics/shading/
> or download the whole project from the repository.
> https://pdfbox.apache.org/downloads.html#scm
> If you want to see the existing code in the debugger with a Gouraud shading, try this
> http://asymptote.sourceforge.net/gallery/Gouraud.pdf
> Testing:
> I have attached several example PDFs. To see which one has which shading, open them with
an editor like NOTEPAD++, and search for "/ShadingType" (without the quotes). If your images
are rendering like the example PDFs, then you were successful.
> Optional:
> Review and optimize the complete shading package for speed; implement cubic spline interpolation
for type 0 (sampled) functions (that one is really low-low priority, see details by looking
up "cubic spline interpolation" in the PDF spec, which tells that it is disregarded in printing,
and I don't have a test PDF).
> Mentor: Tilman Hausherr (European timezone, languages: german, english, french)

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