scanning pages using WIA or TWAIN - c++

Question

Edit: Are there any tutorials on how to use WIA or TWAIN in c++, that explain how to scan pages, adjust settings (DPI, using automatic feeder etc.) and save them as PNG files?
I'd like to use WIA to scan pages and store them as png files. If the scanner supports automatic feeding I'd also like to use that feature. Currently I am following the steps of this tutorial and am stuck at the section Transferring Image Data in WIA 2.0.
So far my scanner has been found and I am able to create the device, and an IWiaItem2* has been created. How can use it to scan at 300dpi and store the result as png file?
The tutorial is not clear about how to start the scan process or how to set dpi for scanning, so I hope someone can help me with the code.
This is essentially the code for getting all local devices:
bool init(IWiaDevMgr2* devMgr)
{
//creating the device manager
*devMgr = 0;
CoCreateInstance( CLSID_WiaDevMgr2, 0, CLSCTX_LOCAL_SERVER, IID_IWiaDevMgr2, (void**)&devMgr);
//enumerating wia devices
IEnumWIA_DEV_INFO* enumDevInfo = 0;
HRESULT hr = devMgr->EnumDeviceInfo( WIA_DEVINFO_ENUM_LOCAL, &enumDevInfo);
if(SUCCEEDED(hr))
{
//loop until an error occurs or end of list
while(hr == S_OK)
{
IWiaPropertyStorage* storage = 0;
hr = enumDevInfo->Next( 1, &storage, 0);
if(hr == S_OK)
{
readProperties(storage);
storage->Release();
storage = 0;
}
}
//set hr to ok, so no error code is returned
if(hr == S_FALSE) hr = S_OK;
enumDevInfo->Release();
enumDevInfo = 0;
}
return SUCCEEDED(hr);
}
void readProperties(IWiaPropertyStorage* storage)
{
PROPSPEC propSpec[2] = {0};
PROPVARIANT propVar[2] = {0};
const ULONG propCount = sizeof(propSpec) / sizeof(propSpec[0]);
propSpec[0].ulKind = PRSPEC_PROPID;
propSpec[0].propid = WIA_DIP_DEV_ID;
propSpec[1].ulKind = PRSPEC_PROPID;
propSpec[1].propid = WIA_DIP_DEV_NAME;
HRESULT hr = storage->ReadMultiple(propCount, propSpec, propVar);
if(SUCCEEDED(hr))
{
Device* dev = new Device(propVar[0].bstrVal, propVar[1].bstrVal);
devices.push_back( dev );
FreePropVariantArray( propCount, propVar );
}
}
Afterwards a device is initialized like this:
bool createDevice(BSTR id, IWiaItem2** item)
{
*item = 0;
HRESULT hr = devMgr->CreateDevice( 0, deviceId, item);
return SUCCEEDED(hr);
}
Then the items are enumerated:
bool enumerateItems(IWiaItem2* item)
{
LONG itemType = 0;
HRESULT hr = item->GetItemType(&itemType);
if(SUCCEEDED(hr))
{
if(itemType & WiaItemTypeFolder || itemType & WiaItemTypeHasAttachments)
{
IEnumWiaItem2* enumItem = 0;
hr = item->EnumChildItems(0, &enumItem );
while(hr == S_OK)
{
IWiaItem2* child = 0;
hr = enumItem->Next( 1, &child, 0 );
if(hr == S_OK)
{
hr = enumerateItems( child );
child->Release();
child = 0;
}
}
if(hr == S_FALSE) hr = S_OK;
enumItem->Release();
enumItem = 0;
}
}
return SUCCEEDED(hr);
}
Now that everything has been initialized I'd like to implement a scan function. However, the code provided at the tutorial is for transferring files and folders and not for scanning images.
void scanAndSaveAsPNG(IWiaItem2* item, unsigned int dpi, std::string targetPath)
{
}
EDIT:
I installed the latest version available of the scanner driver (WIA and TWAIN) and after checking the supported commands using this code
void printCommands(IWiaItem2* i)
{
IEnumWIA_DEV_CAPS* caps = 0;
HRESULT h = item->EnumDeviceCapabilities(WIA_DEVICE_COMMANDS, &caps);
if(SUCCEEDED(h))
{
ULONG count = 0;
caps->GetCount(&count);
if(count > 0)
{
WIA_DEV_CAP* cap = new WIA_DEV_CAP[ count ];
ULONG fetched;
caps->Next(count, cap, &fetched);
for(int i = 0; i < fetched; i++)
{
std::cout << bstr_t( cap[i].bstrName ) << "\n";
}
}
caps->Release();
}
}
I noticed it only lists WIA Synchronize command. I am not sure if I didn't initialize the device correctly, or if the device doesn't support all WIA commands although the driver is installed.
So unless this problem is solved I am alternatively also looking for the same code based on TWAIN.

Answer 1

You want to use IWiaItem2::DeviceCommand which sends a command to the image capture device. The list of commands you can send are listed here.