Get Transparency Status on TIFF images?

A Bridge script here:

Find Layered TIFF Files

I just wrote this code snippet which hopefully parses the TIFF file more reliably... Use it at your own risk...

//  "TIFF - Wikipedia"
//      <https://en.wikipedia.org/wiki/TIFF>
//  "TIFF™ Revision 6.0 Final — June 3, 1992"
//      <https://web.archive.org/web/20160305010142/http://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf>
//
function main ()
{
    function readInt (file, byteCount, bigEndian)
    {
        var bytes = file.read (byteCount);
        var intValue = 0;
        for (var index = 0; index < byteCount; index++)
        {
            intValue = (intValue << 8) + bytes.charCodeAt (bigEndian ? index : byteCount - index - 1);
        }
        return intValue;
    }
    //
    function isTiffFile (f)
    {
        return (f.type === 'TIFF') || f.name.match (/\.tiff?$/i);
    }
    var tiffFilter =
        (File.fs === "Macintosh") ?
            function (f) { return (f instanceof Folder) || isTiffFile (f); } :
            "TIFF Files:*.tif,All Files:*.*";
    var tiffFile = File.openDialog ("Open TIFF file:", tiffFilter);
    if (tiffFile)
    {
        var readonly = tiffFile.readonly;   // Let's work around an odd Photoshop CS bug after a file selection dialog !!
        if (tiffFile.open ('r'))
        {
            tiffFile.encoding = 'BINARY';
            var byteOrder = tiffFile.read (2);
            switch (byteOrder)
            {
                case 'II':  // IBM PC
                case 'MM':  // Macintosh
                    var bigEndian = (byteOrder === 'MM');
                    var magicNumber = readInt (tiffFile, 2, bigEndian);
                    if (magicNumber === 42) // Arbitrary but carefully chosen number...
                    {
                        var hasTransparency = false;
                        var dirOffset = readInt (tiffFile, 4, bigEndian);
                        do
                        {
                            tiffFile.seek (dirOffset);
                            var dirCount = readInt (tiffFile, 2, bigEndian);
                            for (var dirIndex = 0; dirIndex < dirCount; dirIndex++)
                            {
                                var entryTag = readInt (tiffFile, 2, bigEndian);
                                var entryType = readInt (tiffFile, 2, bigEndian);
                                var entryCount = readInt (tiffFile, 4, bigEndian);
                                var entryValueOrOffset = readInt (tiffFile, 4, bigEndian);
                                if (entryTag === 338)   // ExtraSamples
                                {
                                    if (entryType === 3)    // Short
                                    {
                                        var values = [ ];
                                        var entryTypeSize = 2;
                                        var entryValueSize = entryCount * entryTypeSize;
                                        var saveOffset = tiffFile.tell ();
                                        if (entryValueSize > 4)
                                        {
                                            tiffFile.seek (entryValueOrOffset);
                                            for (var valueIndex = 0; valueIndex < entryCount; valueIndex++)
                                            {
                                                values.push (readInt (tiffFile, entryTypeSize, bigEndian));
                                            }
                                        }
                                        else
                                        {
                                            tiffFile.seek (-4, 1);  // Rewind 4 bytes
                                            for (var valueIndex = 0; valueIndex < entryCount; valueIndex++)
                                            {
                                                values.push (readInt (tiffFile, entryTypeSize, bigEndian));
                                            }
                                        }
                                        tiffFile.seek (saveOffset);
                                        for (valueIndex = 0; valueIndex < values.length; valueIndex++)
                                        {
                                            if (values[valueIndex] === 1)   // Associated alpha data (with pre-multiplied color)
                                            {
                                                hasTransparency = true;
                                            }
                                        }
                                    }
                                    else
                                    {
                                         throw new Error ("Invalid entry type (3 expected):\n" + entryType);
                                    }
                                }
                            }
                            dirOffset = readInt (tiffFile, 4, bigEndian);
                        }
                        while (dirOffset);
                        alert ("Transparency:\n" + hasTransparency);
                    }
                    else
                    {
                        alert ("Unknown magic number:\n" + magicNumber);
                    }
                    break;
                default:
                    alert ("Unknown byte order:\n" + byteOrder);
                    break;
            }
            tiffFile.close ();
        }
        else
        {
            alert ("Cannot open TIFF file.");
        }
    }
}
//
main ();
//

[Edit]: Case of extra standard alpha channels is now correctly taken into account.

HTH,

--Mikaeru