[sane-devel] [janitorial] New backend: escl

[Olaf Meeuwissen]

Hi,

# Rearranging top-posted content to the bottom so the conversation makes
# logical sense again :-/

Thierry Hucard writes:

> Le 15 déc. 2019 à 19:56, à 19:56, Ulf Zibis <ulf.zibis at gmx.de> a écrit:
>>
>>Am 15.12.19 um 19:43 schrieb thierry at ordissimo.com:
>>> 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,
--
Olaf Meeuwissen, LPIC-2            FSF Associate Member since 2004-01-27
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