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 <[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, -- Olaf Meeuwissen, LPIC-2 FSF Associate Member since 2004-01-27 GnuPG key: F84A2DD9/B3C0 2F47 EA19 64F4 9F13 F43E B8A4 A88A F84A 2DD9 Support Free Software https://my.fsf.org/donate Join the Free Software Foundation https://my.fsf.org/join
