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

[Thierry Hucard]

Hi,

I'm finishing png support.
Thierry

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Le 17 déc. 2019 à 13:32, à 13:32, Ulf Zibis <ulf.zibis at gmx.de> a écrit:
>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
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