TWAIN backend does not allow to set DPI

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Retrieve Scanner object 
2. Attempt to call scan() method with dpi not set to 200

What is the expected output? What do you see instead?
Expected: scanning the document with desired DPI.
Actual: scanning the document with DPI 200.

What version of the product are you using? On what operating system?
imagescanner 0.9 for python 2.7 on win 7, installed via pip.


Suggested fix:
imagescanner/ backends/ twain/ __init__.py
@lines 53-54
    def _open(self):
        self._src_manager = twain.SourceManager(0)
        self._scanner = self._src_manager.OpenSource(self._source_name)
-       self._scanner.SetCapability(twain.ICAP_YRESOLUTION,
-                                   twain.TWTY_FIX32, 200.0)

@lines 60-61
    def scan(self, dpi=200):
        self._open()
+       self._scanner.SetCapability(twain.ICAP_YRESOLUTION, 
+                                   twain.TWTY_FIX32, dpi)
        self._scanner.RequestAcquire(0, 0)

Original issue reported on code.google.com by [email protected] on 22 May 2014 at 10:01