Detect transparent pixels

[Ghoul Fool]

I'm trying to discover a way of detecting transparent pixels. More over if an image is on a transparent background. Looking at the four corner pixels will be sufficient.

Only I don't think there's a way to detect RGBA as if the code below is run on a transparent pixels it throws an General Photoshop 8800 error. Any ideas? Apart from a try/catch and or trying to copy paste said pixels.

  // Add a Color Sampler at a given x and y coordinate in the image.
  var pointSample = app.activeDocument.colorSamplers.add([(x),(y)]);

  // Obtain array of RGB values.
  var rgb = [
  pointSample.color.rgb.red,
  pointSample.color.rgb.green,
  pointSample.color.rgb.blue
 ];