I will use an external provider to scan 1000+ old slides ("diapositives"), mostly family snapshots made a few decades ago. The provider offers by default standard definition jpg (512 x 340 pixels) and high-definition jpg (3200 x 4800 pixels, 3500 dpi, estimated file size of 5Mb).
As an option (an increase of 30% of the price !!!) they also offer uncompressed TIFF format. I called customer support, and they told me that the resolution (# pixels & dpi) is the same, but quality is higher. They could not tell me which quality settings they use to generate the HD jpg. They also cannot provide the actual file coming from the scanner (I would think the scanner produces some type of RAW or HDR file?), instead of the TIFF.
So I have two questions:
Intuitively, I would think it makes sense to also order the TIFF file for archiving purposes. But if they confirm they make the jpg with 100% quality setting, would it still makes sense to pay 30% more for the TIFF files?
If I do buy the TIFF files as well, which software should I use to batch-convert into jpg ? A web-search gives me tens of options of converters, and I do not find any information about quality differences. Is this because the jpg compression algorithm is fixed/standardized, so high-end software like Photoshop or Lightroom will give the same results as a basic freeware ? Maybe I am confused by the notion of jpg engines that convert RAW, and where some brands like Olympus produce "nicer" looking (subjectively, I know) jpgs than e.g. Lightroom.
I am familiar with GIMP and Imagemagick (but not an expert), so any tips on settings to use ?
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I have sent a request to tech support for additional information about the TIFF file and quality settings of JPG file, and herewith their answer (I have sent a follow-up question, as I did not understand their first two points).
- 8 bits TIFF files come directly from the scanner
- This processing allows for fully exploiting the 12bits from the scanner's CCD
- After post-processing, the images are saved as 8 bits TIFF files (50Mb file size) and 95% quality JPG (typically 3-6MB file size)
- Visually both are indistinguisable
- TIFF only makes sense if someones want to further process the file
Looks sensible to me, but I did not understand the first part. Does the CCD scans at 12bits in total (4bits per channel, which seems very low to me), or 12 bits per channel (hence 36bits). If the latter, not sure why the scanning/capturing software cannot put this in a 16bit TIFF file instead of using 8bit TIFF, hence discarding some potentially useful data.
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I received a follow-up email with further clarifications (please note that the original email is in French, which I translated in English; as I am not a film expert nor a native English speaker, word choices might not be 100% correct).
- The scanner indeed provides 12bits per channel, on a linear scale. This is not very suited for the tonal spectrum/scale of photos, which is rather logarithmic. Therefore, it is very well possible to convert the 12bits linear from the CCD into 8bits tonal/color scale for a photo. In any case, the scanner cannot do any better.
- For more information about the justification for using 8bits, please check the Kodak Cineon format which is based on 10bits, which was largely sufficient to store the images from professional-grade film scanners. For more information, see https://flylib.com/books/en/2.104.1/cineon_log_space.html
- TIFF is very rarely requested, so no samples available so share.
So a quite comprehensive answer. I also had a follow-up call with them, and they say they use very good professional equipment, but their services are aimed at consumers, and this is still below what specialized laboratories use that cater for the professional market. So their scanner's output can be fully captured in an 8bit TIFF and 16bit would have no additional value.
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I will forego the TIFF, and only order the JPG.
If by any chance, some of the diapositives turn out to be really amazing, and we want large prints, it probably is better to re-submit these to a really professional lab, re-scan them with a better scanner, and obtain a RAW or TIFF file for the few photos that are really worth it.
Thanks everybody for your contribution.