How to activate the backlight in HP 4890 scanner

[Anonymous]

I am writing a twain app using a HP 4890 scanner.
Despite a some bugs in the DS software I am able to most of the operations I need.
But I am stuck on how to activate the backlight I need to scan my 35mm slides. It seems like there is no support for this in the DS software.
Am I wrong ?
Is there any workaround ?
I have been thinking of trying to “talk” directly to the scanner via the USB interface, possible ??

Any suggestion is appreciated

John Rehn

[hpb]

The DS for this scanner does not support ICAP_LIGHTPATH.
To scan tranparencies the client has to enable the source UI and set the desired scanning mode from the UI.
You cannot talk to the scanner directly for multiple reasons. The most important one is that neither the interface of the scanner firmware not the interface of the scanner driver is public

[Anonymous]

Thanks for responce, hpb. Do you have “inside information” ? 😉 ( You seems to know more about this than HP support in my country )
Actually, what I might do is to use a usb-sniffer and try to find out how the backlight is activated by the UI.
I have 20y programming experience, but have not worked with the USB interface before. Do you see any reason why such an approach would be -impossible- ?

Eh… maybe.. do you have more info about bugs in the TWAIN interface ?? So I don’t have to find out the hard way :). I have found at least one more case where the interface breaks the spec.

John Rehn

[hpb]

Nothing is impossible. The problem you are facing though is that activating the right lamp is only the beginning of the story. There are a lot of other things to take care of — so it is unlikely that your efforts of reverse engineering will pay off.
As to the tips about this scanner twain problems, I don’t think there is anything really serious I am aware of, but if you have trouble with a particular part of the twain flow, I would gladly answer your questions.

[Author]

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