On 2021-01-23 12:03, John Seberg via PLUG-discuss wrote:
> I think it's likely that DNG is higher resolution - keeps more data.
TIFF allows you to specify the resolution for the image in one of the
standard tags. (The acronym is Tagged Image File Format, after all.)
I've seen TIFFs as high as 2560 pixels/inch in the wild.
> Color depth. This is my first suspicion. By converting DNG to
> TIFF, one might be discarding colors. I've seen color depths as high
> as 64 bit.
That seems excessive. 16 bits/channel is IIRC more depth than regular
humans can perceive.
> Stored attributes. Formats often support attribute/values (a.k.a
> metadata), and TIFF might have some limits, here.
There are a possible 65535 tags in the TIFF specification. Some are
standardized, some aren't. You can store arbitrary data inside any tag.
TypeReader stored OCR information in tags in the non-standardized tag
space with a certain format in its output files. (Yes, I had to
reverse-engineer this in job[-1], it was a pity nothing came of the
project because it was interesting.)
> typically lossless (ZIP or LZW) with TIFF. JPEG compression is lossy,
> and I think that may be a TIFF option to be avoided
Most things do not expect to see JPEG compression inside a TIFF, and
they barfed if presented with such data. Or at least they did the last
time I looked at JPEG-TIFF, which was years ago; things may have
improved.
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