How can I convert a scanned PDF to an image using MATLAB?

How can I import a scanned PDF into MATLAB and convert it to image files?

I tried to use extractFileText() from Text Analytics Toolbox, but it only works for native PDFs and not scanned PDFs:

https://www.mathworks.com/help/textanalytics/ref/extractfiletext.html

>> extractFileText('example.pdf')
ans = 
    <missing>

Answer 1

[MathWorks Support Team]

MATLAB ships with the Apache PDFBox Java library which allows importing and rendering PDF files. Use the following MATLAB function PDFtoImg() to import a scanned PDF, and save each page as a separate PNG file:

function images = PDFtoImg(pdfFile)
import org.apache.pdfbox.*
import java.io.*
filename = fullfile(pwd,pdfFile);
jFile = File(filename);
document = pdmodel.PDDocument.load(jFile);
pdfRenderer = rendering.PDFRenderer(document);
count = document.getNumberOfPages();
images = [];
for ii = 1:count
    bim = pdfRenderer.renderImageWithDPI(ii-1, 300, rendering.ImageType.RGB);
    images = [images (filename + "-" +"Page" + ii + ".png")];
    tools.imageio.ImageIOUtil.writeImage(bim, filename + "-" +"Page" + ii + ".png", 300);
end
document.close()

Notes:

1. It is important to split the input PDF data into images for each PDF page. For example, if “example.pdf” contains 13 pages, then we should convert 13 pages to 13 images.

2. For subsequent OCR tasks, is important to render the PDF pages with 300 dpi or higher resolution:\n

>> bim = pdfRenderer.renderImageWithDPI(ii-1, 300, rendering.ImageType.RGB);

[Douglas Chai]

Works beautifully. Thanks.

[Tan Wai Chun]

Hi, I would like to ask, which code should I use to import scanned PDF? Because i got an error while running the command PDFtoImg().

Thank you :D

[nur alya]

hye, sorry to ask, from the codes given, I just need to replace the pdf file name right? but why it's not working?

[Sagar Hukkire]

@Tan Wai Chun and @nur alya can you please post your error message? make sure your pdf file is in working directory

[Tan Wai Chun]

@Sagar Hukkire Thanks ! I able to get it works already. :D

[Sagar Hukkire]

@Tan Wai Chun I am happy to hear that, all the best

[Patrick Fitzgerald]

Howdy

I'm getting a soft error (and incorrect renders) from the PDFStreamEngine as it tries to read my PDF:

[ERROR] PDFStreamEngine - Cannot read JBIG2 image: jbig2-imageio is not installed

I've researched this issue, and found two trends (e.g. as discussed here https://github.com/levigo/jbig2-imageio/issues/54 ) in the solutions proposed for full Java implementations:

1. Execute ImageIO.scanForPlugins() before instantiating the pdf renderer
2. Adding the JBIG2 package as a dependency in the Java project you're building

I've looked at the .jar contents that install with Matlab, and the content doesn't seem to be missing, just not recognized during Matlab runtime. For this reason, I'm leaning more towards #1 being more the issue.

I've seen an alternative to the Java code suggested in #1 to be this (from same link): IIORegistry.getDefaultInstance().registerServiceProvider(new JBIG2ImageReaderSpi());

I'm not familiar with Java programming, and my understanding of Java in Matlab is limited... How can I translate these fixes to Matlab to make use of the Java functionality that is already installed. I've tried executing these code fixes with some variations, but can't seem to get anything other than Undefined variable ... or class ...

[Patrick Fitzgerald]

Note that in this related question this line (innermost IF block) throws the same error.

xObject = resources.getXObject(key);

Additionally, the import javax.imageio.ImageIO.* code used therein does let me call scanForPlugins() but does not fix anything.

[David Botto]

The sample file above creates a set of png files. How do i read these png files? extractFileText does not work with png files.

[Benjamin Ehrlich]

does this help?

https://www.mathworks.com/help/vision/ref/ocr.html

[Jorge Kuster]

It is possible get the DPI from the pdf with matlab?? and then use these value...

[Suchithra Ramachandran]

I am facing an error with line "pdmodel.PDDocument.load(jFile)"

The error looks like below,

Java exception occurred:

java.io.IOException: Object must be defined and must not be compressed object: 8:0 at org.apache.pdfbox.pdmodel.PDDocument.load(PDDocument.java:995)

Can you pls help in solving this?

[Jianxin Xie]

I have the same issue!

Did you solve this?

[Karolina Charaziak]

For a change I keep getting this error:

Error using PDFtoImg Too many input arguments.

I am using script as posted on mathworkswebinar (weirdly it works when i run it as live script but i get an error when I just copy paste it to the command line)

Answer 2

[Zhongcheng Sun]

I am facing an error with line "pdmodel.PDDocument.load(jFile)", which is "Arguments must contain strings."

could you pls help solve this?