multi_scan not exiting on HP ADF

[twinklebob]

I've got an HP flatbed with an ADF attached.

Using SANE directly I can run batch scans and it will correctly quit after the last page is scanned. However the python-sane library (v2.8.2 installed with PIP) doesn't seem to exit.

A quick scan through the code looks like it uses an exception to tell the iterator to stop, any ideas why that might not be thrown by the SANE backend?

I'm a novice Python developer, so I'm probably doing it wrong, but I've tried:

for i, pageim in enumerate(dev.multi_scan()):
    pageim.save('test ' + str(i) + '.png')

and

i = 0
while dev.multi_scan():
    dev.multi_scan().next().save('while_test_' + str(i) + '.png')
    i = i + 1

But to be honest even a single scan will continue if there is no paper:

dev.start()
im = dev.snap()
im.save('test_pil.png')

Let me know what you need from me to debug this.

[manisandro]

The relevant piece of code is

def next(self):
    try:
        self.device.start()
    except Exception as e:
        if str(e) == 'Document feeder out of documents':
            raise StopIteration
        else:
            raise

The first thing to try would be whether an exception is raised at all, and possibly just with a different message (i.e. other than Document feeder out of documents).

[twinklebob]

It doesn't seem to raise an exception at all, at least not one that Python picks up. As I say, Python isn't my primary language, does raise rethrow the earlier exception, or would I need to explicitly rethrow it?

[twinklebob]

Did a quick and dirty, added print str(e) as the first line in the except block and it's not hitting that at all, so apparently no exception being thrown by SANE.

It's a pretty old scanner, it has to be said, but if anything I'd expect it to complain quite loudly! :-)

[twinklebob]

Here's the output from scan-image if I put no documents in the feeder

scanimage --mode Color --resolution 150 --depth 8 -x 210 -y 297 --source ADF --batch --format=pnm

scanimage: rounded value of br-y from 297 to 296.888
Scanning -1 pages, incrementing by 1, numbering from 1
Scanning page 1
scanimage: sane_start: Document feeder out of documents

Could it be because I haven't expressly set the source to be the ADF?

[twinklebob]

It was!

dev.source = "ADF"

Was all it needed. Any chance you could add an example of using the multi_scan() to the documentation, because I'm doing a lot of guessing here.

Sorry for wasting your time! :smile:

[manisandro]

Hmm I actually never tested with an ADF scanner (don't even have access to one), so I wonder if all devices require this or if it is device dependent. If all devices require it, one could set the option directly in multi_scan (and the set the option to the corresponding value for non-ADF mode when doing scan or snap). But as I said, I have no idea whether source=ADF is in any way a standard requirement.

[twinklebob]

Well, for the record, is was definitely needed with my ancient HP. It looks like once the feeder was empty it just used the standard bed. I should've guessed by the content of the image, really, as it had scanned the entire bad, not just the section where it normally reads the ADF documents. I'd guess that most combination scanners will do the same, use the document feeder if populated or just assume that you're doing a flatbed scan otherwise, but I have no way of knowing.

[prudhvi-cmx]

I also have HP Flatbed with ADF. I tried batch scans using dev.source = ADF as and

for i, pageim in enumerate(dev.multi_scan()): pageim.save('test ' + str(i) + '.png')

It doesn't seems to exit when I am scanning more than 3 pages at a row. Is there anything I am missinghere?

Do let me know. Thanks in Advance

[hamburgercheeseburger]

python-sane doesn't detect my device every time

1st it detects and scans normally but after the first scan it doesn't detect any device