Hi Olaf,
Am 17.12.19 um 12:36 schrieb Olaf Meeuwissen:
Thierry Hucard writes:
Le 15 déc. 2019 à 19:56, à 19:56, Ulf Zibis <[email protected]> a écrit:
Am 15.12.19 um 19:43 schrieb [email protected]:
Le 2019-12-15 18:34, Ulf Zibis a écrit:
Hi List,
Am 15.12.19 um 09:10 schrieb Olaf Meeuwissen:
The backend currently only supports image data transfer in JPEG format
but Thierry indicated he wanted to add support for PNG and PDF as well.
Would it be possible to also support the TIFF format, as for
black&white it is the best compressing with Fax G4 compression?
I didn't see any device managing Tiff, send me the capability file,
I could add the support.
[...]
In my understanding, it's not the scanner, which supports the TIFF
format, but it has to send raw (or lossless compressed) format, so
sane or the sane frontend could compress to TIFF.
No the backend receives the scanner data (the jpeg format always seems
to be present), it can be jpeg, png, pdf or octet-stream. I didn't see
any tiff. The data is compressed and sent back to the frontend.
As Thierry indicated, the JPEG support by the escl backend is a matter
of the communication between the device and the backend. For any SANE
frontend, that doesn't really matter as the SANE Standard only allows
for a "raw" image format. Any backend *has* to convert to SANE's raw
image format before handing image data to the frontend.
Doing device-backend image data transfer using JPEG is lossy in all but
the most uncommon scenarios. That is, image quality suffers. If the
device-backend image data transfer can use PNG, which is not lossy, that
would be a big improvement, image quality-wise.
BTW, I fear that any PDF device-backend image data transfer is just a
JPEG image wrapped in PDF but that remains to be seen.
Wishful thinking says PNG-in-PDF is out there somewhere, maybe.
Hope this helps,
Yes it helps to understand the issue, much thanks.
If escl becomes common in future, I can imagine, sane additionally could
provide a JPEG format interface to benefit from the faster transmission
between scanner and backend, especially if the transport is over network
and image quality doesn't matter so much.
-Ulf
