Get colour sample from transparent pixel - transparency

Question

I'm trying detect if a pixel is complete transparent or not. More specifically, if an image is on a transparent background or not. I thought that
// 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
];
would work - and it does...
Unless the pixel has 0% opacity (ie 100% transparent) in which case Photoshop throws a General 8800 error. I would use the above with a try catch but that probably isn't the way to go about it.
Any ideas?

Answer 1

Well I found a way to determine if an image has transparency or not:
delete_all_colour_samples();
var isImageTransparent = has_transparency();
var x = 0;
var y = 0;
alert(isImageTransparent ? "Image has transparency." : "Image is opaque.");
if (isImageTransparent)
{
// do stuff
}
else
{
// get colour sample
// 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
];
}
// function to see if image has transparency
function has_transparency()
{
var desc52 = new ActionDescriptor();
var ref47 = new ActionReference();
ref47.putProperty( charIDToTypeID('Chnl'), charIDToTypeID('fsel') );
desc52.putReference( charIDToTypeID('null'), ref47 );
var ref48 = new ActionReference();
ref48.putEnumerated( charIDToTypeID('Chnl'), charIDToTypeID('Chnl'), charIDToTypeID('Trsp') );
desc52.putReference( charIDToTypeID('T '), ref48 );
desc52.putBoolean( charIDToTypeID('Invr'), true );
try
{
executeAction( charIDToTypeID('setd'), desc52, DialogModes.NO );
}
catch(eek)
{
return false;
}
activeDocument.selection.deselect();
return true;
}
function delete_all_colour_samples()
{
// Kill all colour samples
app.activeDocument.colorSamplers.removeAll();
}