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

[Ulf Zibis]

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 <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,

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