Capture/Image Source

How can I use a custom capability of my scanner hardware when there is no direct API to set it?

You can use Capability Negotiation to set it. Capability Negotiation is the way a TWAIN application communicates with a TWAIN source. This is how Dynamic Web TWAIN communicates with a scanner. The process looks something like this:

• [Dynamic Web TWAIN] Are you capable of ***?
• [Scanner] Yes, and here is what I can do…
• [Dynamic Web TWAIN] Great, here is what I want done…
• [Scanner] Consider it done

The steps are:

• Step-1 - Use getCapabilities to find the capability you want to set.

DWObject.OpenSource();
DWObject.getCapabilities(
  function () {
    console.log(arguments);
  },
  function (error) {
    console.log(error);
  }
);

• Step-2 - Use setCapabilities to set the capability.

DWObject.setCapabilities(
  {
    exception: "ignore",
    capabilities: [
      {
        capability: Dynamsoft.DWT.EnumDWT_Cap.ICAP_CONTRAST,
        curValue: 500, // set the contrast to 500
        exception: "fail",
      },
    ],
  },
  function (result) {
    console.log(result);
  },
  function (error) {
    console.log(error);
  }
);