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natrev
natrev
Legend
August 16, 2017
Answered

Get Transparency Status on TIFF images?

  • August 16, 2017
  • 3 replies
  • 3467 views

Hi EveryOne!

Sorry for the same question again.

Is this possible to get transparency status on TIFF image using javascript? (or) is this possible via bridge script?

Whether it is checked ON/OFF( true / false ).

Any help or suggestion much appreciated.

-yajiv

This topic has been closed for replies.
Correct answer c.pfaffenbichler

I suspect this may be a fairly inefficient method, but you could give it a try:

// based on code by paul riggott;

// 2017, use it at your own risk;

var file = File.openDialog("Please select tif file.","tif File:*.tif");

main(file);

function main(file){

file.open("r");

file.encoding = 'BINARY';

filestring = file.read();

file.close();

if (filestring.indexOf("Transparency") != -1) {alert ("has transparency")}

};

3 replies

Stephen Marsh
Community Expert
Stephen MarshCommunity Expert
Community Expert
August 17, 2017

A Bridge script here:

Find Layered TIFF Files

A
Anonymous
August 16, 2017

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

    natrev
    natrevAuthor
    Legend
    August 17, 2017

    Thank you Chris, 

    Thank you Mikaeru69,

    I have learned new thing from both of your knowledge.

    I have question on mind, Same as is it possible to get Layer compression whether its Zip or RLE.

    I tried but I am not able to find the solution. Any help or suggestion much appreciated.

    -yajiv

    natrev
    natrevAuthor
    Legend
    August 18, 2017

    I just did a few investigations:

    - When Layer Compression is either 'RLE' or 'ZIP', the tag 37724 gets defined (will appear in the variable entryTag in the above code).

    - When Layer Compression is 'Discard', the tag 33723 is defined instead.

    - According to the page TIFF tags, the tag 37724 is ImageSourceData​, privately used by Adobe Photoshop. It is described in the document Photoshop TIFF:

    Adobe Photoshop specific image source data tag. This section has the layer and mask information found in a typical layered Photoshop file.

    Field: ImageSourceData

    Tag: 37724 (935C.H)

    Type: UNDEFINED

    Count: number of bytes for section

    The section starts with a character string of "Adobe Photoshop Document Data Block" including the null termination character.

    The remainder of the count, after subtracting the length of the above mentioned string, is a series of tagged data types in the following format:

    • 4 bytes Signature ‘8BIM’
    • 4 bytes Type various types (see below)
    • 4 bytes Length length in bytes, variable for each type, padded to a 4 byte offset

    The various types are mentioned here with further documentation in the Photoshop File Formats.pdf.

    The available types are:

    • ‘Layr’ Layer Data
    • ‘LMsk’ User Mask     Same as Global layer mask info table
    • ‘Patt’ Pattern
    • ‘Anno’ Annotations

    - Now, all you have to do is to consult and understand the above-mentioned document Adobe Photoshop File Formats Specification to access the relevant information... BTW, there is also a Photoshop-specific TIFF Tags section listing all the specific tags.

    Good luck!

    --Mikaeru


    Hi Mikaeru,

    Thank you so much for your information about TIFF tags. Now I have a clear outline on the TIFF tags and function.

    -yajiv

    c.pfaffenbichler
    Community Expert
    c.pfaffenbichlerCommunity ExpertCorrect answer
    Community Expert
    August 16, 2017

    I suspect this may be a fairly inefficient method, but you could give it a try:

    // based on code by paul riggott;

    // 2017, use it at your own risk;

    var file = File.openDialog("Please select tif file.","tif File:*.tif");

    main(file);

    function main(file){

    file.open("r");

    file.encoding = 'BINARY';

    filestring = file.read();

    file.close();

    if (filestring.indexOf("Transparency") != -1) {alert ("has transparency")}

    };

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