Size of scanned text vs. scanned image

jmt356
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Size of scanned text vs. scanned image

Post by jmt356 »

Is a 400 x 400 dpi scanned image file larger than a 400 x 400 dpi scanned text file?
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HansV
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Re: Size of scanned text vs. scanned image

Post by HansV »

That depends on the file format. If you save the scanned files as .bmp, the file format depends entirely on the physical size of the scanned page.
If you save as for example .jpg or .png, a page can be compressed further than a photograph.
And if you apply OCR to the text page, the resulting text file should be relatively small.

But why don't you experiment?
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jmt356
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Re: Size of scanned text vs. scanned image

Post by jmt356 »

What if I am saving files as TIFs or JPGs and not compressing them or applying OCR? Is the file size for an image the same as text on a page of the same physical size?
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HansV
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Re: Size of scanned text vs. scanned image

Post by HansV »

A .jpg file is always compressed. A .tiff file can be compressed, but not necessarily so.
For an uncompressed image, the file size is determined by the physical size of the image (and the color depth - a black-and-white scan will take up less space than a full color scan).
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jmt356
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Re: Size of scanned text vs. scanned image

Post by jmt356 »

So if I have two 8.5 x 11 documents, one with a black and white drawing and the other with black and white text, and I scan them as TIF files, both will be the same size?

What if I scan them as JPGs? Will both be the same size?
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StuartR
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Re: Size of scanned text vs. scanned image

Post by StuartR »

Why don't you try it and see. It is almost impossible to predict how well something like that will compress, especially without seeing it.
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HansV
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Re: Size of scanned text vs. scanned image

Post by HansV »

As Stuart indicates, it's hard to predict. A simple line drawing will compress better than a complicated patterned drawing.
So gather some samples of text and drawings, scan them to .tif and to .jpg, and compare the results.
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jmt356
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Re: Size of scanned text vs. scanned image

Post by jmt356 »

I can't test with jpgs but this is what I was able to test:

FOR PDF FORMAT (B&W SCAN)
A complex photo came out to 164 KB
A blank page with three letters written on it came out to 2 kb

FOR TIFF FORMAT (B&W SCAN)
A complex photo came out to 1 MB
A blank page with three letters written on it came out to 1 kb

Based on this information, is it correct to assume that the scanner is compressing both PDFs and TIFF files, since otherwise, the photo and blank page with 3 letters on it would come out the same size, since they are the same physical size and color depth (b&w)?
Last edited by jmt356 on 11 Mar 2012, 19:05, edited 1 time in total.
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StuartR
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Re: Size of scanned text vs. scanned image

Post by StuartR »

Clearly the scanner software is compressing both files under these exact circumstances. This does not tell you about what compression would be applied to other text and images.
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