Hi, I know that the user can save a pdf as an image (or rather as a series of images). And I know that saving to a jpg is not lossless. But what about saving to a png? Is this lossless?
If not, then my question becomes general: does Acrobat give the user a lossless way to save a pdf as an image?
I just tested both PNGs and TIFFs. I think both are lossy.
I saved a pdf as a png, opened it in Acrobat ("Convert to Adobe Acrobat), saved it as a png again, and opened it again, etc. After a while, ugly compression artifacts began appearing.
Am I missing something? Thanks.
Strictly speaking TIFF files could be lossy. TIFF files can include various compression methods, including JPEG, which would be lossy. But this is almost never used, they use LZW or ZIP both of which are lossless. PNG uses ZIP always.
JPEG2000 is NOT automatically lossless. It comes in lossless and lossy flavours, and Acrobat can use either.
(For that matter, there is also a lossless JPEG, but that is really never, never, used).
Where a file format offers options on saving, check them, as you can sometimes choose whether to have a lossless or lossy format. To emphasise: LZW and ZIP are always lossless.
Actually, I think we missed a very important point at the beginning. Saving PDF pages to an image almost always causes severe quality losses that are nothing to do with compression. Here's why.
A PDF is a mixture of some or all of:
- vector art (shapes, lines, etc.)
- raster images (originally TIFF, JPEG or whatever) at DIFFERENT resolutions
Now, if you save a page of a PDF to a raster format, then what happens to the above is:
- text must be converted to a raster format. It is no longer text, free to scale and sharp to read at anysize
- vector art must be conveted to a raster format with similar losses to text
- raster images have to be converted to the final resolution. Unless the resolution of the image and of the exported graphic happen to be the same there will be quality losses
So, whether you choose JPEG, PNG or whatever, it is only in a very small set of circumstances lossless. That is, when the PDF contains nothing but raster images, all at the same resolution, which is the same as the exported resolution.
Dave, thanks for helping to answer the question. I do not quite understand your use of the terms 'claim' and 'fact' as somehow mutually exclusive in general, nor their application to this case in particular (especially in light of the interesting contributions of Test Screen Name).
Just to expand on the save issue a bit. One way to get the graphics out is to export images in the tools. That will pull all of the images into separate files. It does not save the pages, but just the bitmap images.
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