I'm attempting to scan some documents with basic science and math diagrams in black and white that can be emailed. The challenge is that some of the pages contain diagrams with gray shading. Many of the reduction tools I've used either remove the shading or change its tone. I have to keep to be able to distinguish among 3 shades of gray, for example, in a bar graph.

The 40 page document at 600DPI in PDF format comes in around 18mb. This approach keeps the image quality that I need, but I'd like to reduce the file size to 5-10mb. I can rescan the document with any settings.

I have an Epson ES400 for scanning. I have all Adobe programs, but I've been using Epson Scan 2 with the scanner.

Would it be better to create a TIFF format? I want to keep the pages as one document.

Here is a sample image with shades of gray at 600dpi.

  • If file size is a paramount concern... ideally, recreating such graphs in vector format would offer the smallest file size. – Scott Apr 23 at 15:31

If file size is the main issue, I would scan this and save it as a high quality JPEG or PNG. TIFFs are usually too large for emails, plus they wont display in most browsers or email clients.

If the original is colour or black with grey and white, then scan it colour, and change the image mode to greyscale in an image editor such as GIMP (free) or Photoshop (not free), or if your scanner has a greyscale mode, use that.

If you do want to send a large TIFF image (or any large file), use a file sharing website such as Dropbox. Send only the image link via email, not the actual image itself.

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  • The document is 40 pages with mostly text. There are 10-15 diagrams. The scan, however, needs to differentiate the shades of gray. My attempts to use PNG result in individual pages. Most importantly, it's important that I can convert to PDF so the end-user can easily download and view. – hammerman20 Apr 23 at 18:44
  • Perhaps you need to check what options are available in your scanner software. You could easily crop the images in an image eidtor. Software that can export PDFs includes Photohsop, GIMP, Inksape, Illustrator, InDesign, Scribus, MS Word, LibreOffice, etc, etc – Billy Kerr Apr 24 at 8:43

The file size problem comes from storing the white space as pixels. Greyscale is one byte per pixel regardless of color. And you are basically just encapsulating full-page raster images in a PDF wrapper.

So the best solution without remaking the graphs is to OCR the text, place that as text in a new indesign document, and then place the graphs as images. This reduces the amount of raster data stored in the PDF and will reduce the PDF file size considerably. You can then experiment with your PDF export "downsample images when above x ppi" to see if you can hit your target file size.

The first alternative to this is to simply edit your PDF export settings (or process the PDF in acrobat) to downsample lower resolution until you cannot stand how bad it looks.

Unlike raster images, InDesign and PDF documents can have images and objects of random resolution across a logical page and printed text is very tolerant of quality reduction. So one thing you can try: make a secondary copy of the PDF with very low resolution that still allows you to read the text; place it in indesign, and then overlay the full-res graphs on top of the poor quality graphs. (place that PDF page, size the box to only include the graph, place it directly on top of the low res version)

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  • Really interesting. I never considered breaking the page in InDesign. Unfortunately, that approach would be too time intensive. For now, I'm using 600DPI with -5 contrast, which results in 17mb for 40 page document. I will keep playing around with the scan settings and see if I can find a solution. – hammerman20 Apr 25 at 14:44

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