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"Zak" schreef in bericht
I use XP.
I scan a document to a graphics file (eg jpg, gif, bmp, etc) Then I make a PDF from the graphics file.
I see that if I save a large bitmap (BMP) and then create a PDF then the PDF is no bigger than if I had compressed the image to a GIF and used that to create a PDF file.
In order to preserve quality, avoid artefacts and interference patterns, would it be better to save to a large and detailed intermediate file like a BMP (or even a jpeg) or to save to a small lossless file like a GIF or TIF?
On 26 May 2006, Nils wrote:
Afaik, GIF is not used as a graphical format inside PDF. It is probably compressed as a "TIFF" with Cittfax or LZW compression. "TIFF" is between brackets, because the embedded stream is also not a complete TIFF file, just contains the compressed graphics and some extra information like scansize, colordepth, color channels, etc.
What happens under the hood in your PDF creation really depends on the PDF engine you’re using. Many engines actually resize your graphics to match the PDF DPI resolution. If you’re an experienced programmer you could try to generate the PDF yourself, with the images in full resolution. The PDF specification is open and can be found on the Adobe website.
Nils
Hi Nils and others. I understand now that when I create a PDF from a image file that the format of the image file is not used inside the PDF. Instead some other format is used in the PDF (which Nils kindly suggests may be a specialized form of TIFF).
It is this conversion from my image file format to the internal PDF format which I want to be done smoothly. I am on XP and I am wondering if it is better to start with a GIF or a JPG or BMP or whatever to feed into my PDF creation utility.
I should say that I am starting with a hard copy of a document created on a word processor. I want to avoid artefacts, unecessarily jagged lines, moire effects and all that stuff which might come from transforming from an "awkward2 image format to a PDF.
My PDFs will be for public distribution. I have preferred to scan to a GIF file rather than a TIFF because I have assumed that when I circulate the basic image file among certain people that the best balance between image size and the best chance of them being able to see the file is a GIF.
To me TIFF feels a bit specialized. For example, I never see a web page with TIFF images but I see lots of pages with GIFs.
Also there seem to be various compression options for a TIFF (group 3 or 4, LZW, JPEG deflate, none) which might makes it even harder for me to know what to choose as a common format! The Wikipedia says documents are often scanned to TIFF group 4 but is that something which has the best chance of being seen on various PCs in various organisations that I might need to send it to?
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