[sane-devel] scanning negatives using HP4850 and genesys backend

[7xsuazlhhtls at gmail.com]

Thanks for the additional info.

I don't have a machine running Windows so USB captures from that 
platform aren't possible at the current time.

Jon

On 7/31/26 12:18 PM, Ralph Little wrote:
> Hi,
> There are other backends that support transparency but the genesys 
> chips are pretty much a world of their own. On the upside, the GL646 
> is pretty well documented.
> I believe the main ways in which the transparency support would be 
> invoked would be via the source and options related to capture type. I 
> don't see any specific image capture type-related options in the 
> backend but some would have to be added I suspect (e.g. for selecting 
> between positive and negative, IR etc).
>
> The main challenge with genesys-based devices is that every model is 
> different to every other in implementation. The Genesys chips are very 
> flexible and offer all sorts of driving options and they need to be 
> set up for the particular hardware that they are matched with. The 
> main way to tackle this task is to observe Windows driver behaviour 
> through capturing traffic and looking at the register values that are 
> set. It's a little more involved but that is the main gist.
>
> I have had some dealings myself with looking at a GL646 device before 
> although it was a fairly superficial look at motor stepping tables but 
> I may be able to look at it in the future sometime.
> One thing you *can* do (if you have the inclination) is to make some 
> USB captures on Windows and post them to an issue at our GitLab issue 
> tracker (https://gitlab.com/sane-project/backends/-/work_items), if 
> you don't intend to do the implementation yourself. That way someone 
> could pick up the issue at some point. Ideally a developer needs the 
> hardware at hand, but a rough stab could be made by looking at the 
> traffic.
>
> Cheers,
> Ralph
>
> On 2026-07-31 10:01, 7xsuazlhhtls at gmail.com wrote:
>>
>> Ralph,
>>
>> Thanks for the reply.
>>
>> I looked at the Genesys Datasheet for the chip (GL646USB) that is 
>> used in the HP4850.  I see the register that appears to control the 
>> slide scanning lamp.
>>
>> Is there another backend that has support for a similar feature? 
>> Possibly I could use that as a template to better understand how 
>> support for this feature might be implemented in the genesys backend.
>>
>> Thanks again,
>>
>> Jon
>>
>>
>> On 7/31/26 11:21 AM, Ralph Little wrote:
>>> Hi,
>>> According to our Supported Scanners list 
>>> (http://www.sane-project.org/sane-supported-devices.html) the 
>>> genesys backend doesn't yet support the slide scanning feature of 
>>> this device. It requires additional code to drive the extra hardware 
>>> involved.
>>> We don't have an active maintainer for the genesys backend at the 
>>> moment unfortunately, so I don't know when someone would be able to 
>>> get to this task in the future. :(
>>>
>>> Regards,
>>> Ralph
>>>
>>> On 2026-07-30 20:58, 7xsuazlhhtls at gmail.com wrote:
>>>>
>>>> |I recently acquired an HP Scanjet 4850 scanner. The document 
>>>> scanning works with no problems.  This particular scanner has a 
>>>> negative/slide scanning component built in to the lid of the 
>>>> device.  This includes a separate lamp to illuminate the film for 
>>>> scanning.  The lamp in the lid comes when I run a hardware self 
>>>> test procedure but I have not discovered any way to have the lamp 
>>>> come on when scanning using sane.
>>>>
>>>> Is this capability supported?
>>>>
>>>> info about my setup ---
>>>>
>>>> HP Scanjet 4850
>>>>
>>>> $ scanimage -V
>>>> scanimage (sane-backends) 1.4.0; backend version 1.4.0
>>>>
>>>> genesys backend
>>>>
>>>> Fedora Linux 44 (Workstation Edition)
>>>> Linux 7.1.5-200.fc44.x86_64|
>>>>
>>>
>
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