Custom and Auto Page Sizes

An application can set page size either through automatic detection by the scanner or through custom values. The approach used by the application is determined by the WIA_IPS_PAGE_SIZE property, which can take the values WIA_PAGE_AUTO or WIA_PAGE_CUSTOM.

If an application sets WIA_IPS_PAGE_SIZE to any value other than WIA_PAGE_CUSTOM, the WIA minidriver should adjust the values of WIA_IPS_PAGE_WIDTH and WIA_IPS_PAGE_HEIGHT to the page's dimensions in thousandths of an inch (.001). The minidriver should also adjust the values of WIA_IPS_XEXTENT and WIA_IPS_YEXTENT to the page's dimensions, in pixels.

If an extent setting (WIA_IPS_XEXTENT or WIA_IPS_YEXTENT) is changed to a value that does not match the current page-size setting, the minidriver should change the value of the WIA_IPS_PAGE_SIZE property to WIA_PAGE_CUSTOM. The minidriver should also modify WIA_IPS_PAGE_WIDTH or WIA_IPS_PAGE_HEIGHT to agree with the new extent setting.

If an application sets the WIA_IPS_PAGE_SIZE property to WIA_PAGE_CUSTOM, the current selection area is not affected. The WIA minidriver should obtain the current image layout, starting from the current settings of the WIA_IPS_XPOS and WIA_IPS_YPOS properties. If the page-size setting cause the selection area to be outside the scanner's bed, the minidriver must automatically adjust the values of the WIA_IPS_XPOS and WIA_IPS_YPOS properties to valid settings. If the WIA_IPS_PAGE_SIZE and WIA_IPS_ORIENTATION properties are set at the same time and they are invalid when they are applied in combination, the minidriver should fail the application's settings by returning an error in the IWiaMiniDrv::drvValidateItemProperties method.

When automatic page size detection is enabled, the driver should provide accurate image dimension information only after completing the transfer of the image data. For stream-based transfers, the driver is expected to update the image dimensions in the image header at the end of the transfer. At the beginning of a new session, the value for the WIA_IPS_PAGE_SIZE property should be always set to a value other than WIA_PAGE_AUTO.

When WIA_PAGE_AUTO is set as the current WIA_IPS_PAGE_SIZE value, the driver might need to first transfer an image header that contains generic image dimensions, then transfer the image data, and then go back to the beginning of the transfer stream, update the image header with the actual image dimensions (found after the scan completed), and move the stream index back to the end of the stream.

When WIA_PAGE_AUTO is set (chosen as the default value by the driver or set by the application), the application should not attempt to process the image dimensions that the image header describes until the entire image transfer is completed.

Note  The compatibility layer within the WIA service does not add support for WIA_IPS_PAGE_SIZE to the ADF item that is translated from a Windows XP WIA device if the property is not supported on the child item of the device. Applications should not expect an ADF item to always support this property and should always check if WIA_IPS_PAGE_SIZE is supported at run time. (Typically, applications should check the support for any property that is to be negotiated.)