Forgot to preface this response with:
The first example code will run your solution synchronously.
On Mon, Jun 8, 2020 at 10:07 AM Brian Yeh <heyna...@gmail.com> wrote:
>
> import Tesseract from 'tesseract.js';
> import pdfimage from 'pdf-image';
>
>
> var PDFImage = pdfimage.PDFImage;
> var pdfImage = new PDFImage(pdfFilePath, { convertOptions: { "-density":
> "196" }});
>
>
> function recursiveFunction(pageIndex, numberOfPages)
> {
> if (pageIndex > numberOfPages) {
> return;
> }
> pdfImage.convertPage(pageIndex).then(function (pageImage) {
> Tesseract.recognize(pageImage, 'eng').then(({ data: { text } }) => {
> console.log(text);
> //perform other synchronous processing with the text before moving to
> the next page...
> recursiveFunction(pageIndex, numberOfPages + 1)
> });
> });
> }
>
> recursiveFunction(0, numberOfPages)
>
> Additionally if each page processing does not rely on previous results for
> generation I would not go the synchronous route. If you need the results
> ordered as if it was synchronous you can simulate this with preallocated
> array where each page is an index. See below:
>
> import Tesseract from 'tesseract.js';
> import pdfimage from 'pdf-image';
>
>
> var PDFImage = pdfimage.PDFImage;
> var pdfImage = new PDFImage(pdfFilePath, { convertOptions: { "-density":
> "196" }});
>
> var acc = [];
> for(var pageIndex = 0; pageIndex < numberOfPages; pageIndex++)
> {
> let currentPageIndex = pageIndex; //Make sure you do this!! node closures
> will reference the wrong pageIndex otherwise!
> pdfImage.convertPage(pageIndex).then(function (pageImage) {
> Tesseract.recognize(pageImage, 'eng').then(({ data: { text } }) => {
> console.log(text);
> //perform other processing with the text before moving to the next
> page...
> //Save the result as a variable.
> acc[currentPageIndex] = results;
> });
> });
> }
>
> The end result of the above code is that all processes will be done async but
> when everything is finished your results will be saved in an array in an
> ordered format from the first page to the last.
>
> Btw I'm not a node expert, just a generalist programmer, honestly not even
> that into node... so someone else may have a better idea how to do this
> idiomatically.
>
>
> On Monday, June 8, 2020 at 2:25:05 AM UTC-7, Matthew Hamilton wrote:
>>
>> I'm relatively new to JavaScript programming for node.js, and I've been
>> reading about this for 5 hours and cannot wrap my head around it, so here I
>> am... I am trying to get the text from a PDF for searching. I need page
>> numbers, line numbers, and character positions of the results. It appears
>> that pdf.js cannot keep line breaks at the very least. I wonder if it will
>> keep multiple sequential spaces, but the line breaks are a dealbreaker, so
>> I've moved on. Now I'm using pdf-image to convert the pdf document to a png
>> for each page. Then I want to use tesseract.js to run OCR on the png files
>> to get the text as it appears in the pdf including line breaks and extra
>> spaces. The problem is if the pdf document is more than 5-10 pages, then
>> execution kills my laptop. The process of converting the pdf to png's
>> consumes over 12GB of RAM and never finishes to even move on the the OCR
>> which has to be worse. The average number of pages in the pdf documents I am
>> processing is 300-500, so I have to batch process. The problem I have is
>> that pdf-image and tesseract.js both use promises for async processing. It's
>> really the async that's killing my laptop. I just want to get the number of
>> pages, loop over each page one at a time, convert it to png, then perform
>> the OCR, then finish some other synchronous processing before moving on to
>> the next page. The code I have right now that doesn't work is:
>>
>> import Tesseract from 'tesseract.js';
>> import pdfimage from 'pdf-image';
>>
>> var PDFImage = pdfimage.PDFImage;
>> var pdfImage = new PDFImage(pdfFilePath, { convertOptions: { "-density":
>> "196" }});
>>
>> for(var pageIndex = 0; pageIndex < numberOfPages; pageIndex++)
>> {
>> pdfImage.convertPage(pageIndex).then(function (pageImage) {
>> Tesseract.recognize(pageImage, 'eng').then(({ data: { text } }) => {
>> console.log(text);
>> //perform other synchronous processing with the text before moving to the
>> next page...
>> });
>> });
>> }
>>
>> I can process one page without the for loop in about 200ms, but when I try
>> to loop everything gets messed up. I'm not sure how to proceed with
>> processing these promises synchronously. I know promises are supposed to be
>> more efficient, but sometimes order is important and resources are limited
>> for unchecked parallel processing... Like file type conversion and OCR for
>> 300-500 page documents.
>>
>> As a nice-to-have, I would also like to figure out how to load and
>> initialize tesseract.js once and then just call the recognize method. I have
>> tried the following code to achieve that, but I think it loads and
>> initializes then reloads and initializes when it calls the recognize method.
>> Controlling that behavior may not be possible, but I figured I'd throw it
>> out there.
>>
>> (async () =>
>> {
>> await Tesseract.load();
>> await Tesseract.loadLanguage('eng');
>> await Tesseract.initialize('eng');
>> });
>>
>> //then perform the convertPage then recognize as shown in the first code
>> block above...
>>
>> Thank you!
>
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