Looping through channels is really slow in CC

[Daikazu]

I've been working on .Net application and ran into a little performance snag. I have a simple method that loops through the channel layers by index, grabs the indexed channel name, and if it matches a predetermined variable then it simple deletes that channel. It works as written but is painfully SLOW. Being fairly new at programming I figured it was just me and opened up ExtendScript to run a few test.

var docChannels = app.activeDocument.channels;
for (i = 0; i < docChannels.length; i++ ){
        alert(docChannels.name);
}

To run this script in a document containing only the RGB channels plus 3 other alpha channels takes approximately 30 to 40 seconds. Running the same script modified to cycle through about 20 document layers only takes about 5 seconds.

I don't know if this is a bug in Photoshop CC or not. I don't have any earlier versions to test on. I've can accomplish the programing method by using a Try Catch statement and directly trying to delete the layer by name. This seems to run a little bit faster but not by much and is not really a proper use of a Try Catch statement.

Any insight into this problem or a better way to impliment my programing method would be most appreciated.

[Michael_L_Hale · Accepted solution]

I am not sure about .Net apps but I think the reason the javascript Object Model can be slow when working with layers and channels it every time you create a layer or channel object all the properties of that object created. I think building the histogram property is the biggest reason for the slow down. Especially is the document has a large canvas.

Action Manger can be much faster because you can get only the property you need and avoid creating a DOM object and building the histogram. Try this to see if faster getting the channel names.

function getProperty( psClass, psKey, index ){// integer:Class, integer:key
    var ref = new ActionReference();
    if( psKey != undefined ) ref.putProperty( charIDToTypeID( "Prpr" ), psKey );
    if(index != undefined ){
        ref.putIndex( psClass, index );
    }else{
        ref.putEnumerated( psClass , charIDToTypeID( "Ordn" ), charIDToTypeID( "Trgt" ) );
    }
    try{
        var desc = executeActionGet(ref);
    }catch(e){ return; }// return on error
    if(desc.count == 0) return;// return undefined if property doesn't exists
    var dataType = desc.getType(psKey);
    switch(dataType){// not all types supported - returns undefined if not supported
        case DescValueType.INTEGERTYPE:
            return desc.getInteger(psKey);
            break;
        case DescValueType.ALIASTYPE:
            return desc.getPath(psKey);
            break;
        case DescValueType.BOOLEANTYPE:
            return desc.getBoolean(psKey);
            break;
        case DescValueType.BOOLEANTYPE:
            return desc.getBoolean(psKey);
            break;
        case DescValueType.UNITDOUBLE:
            return desc.getUnitDoubleValue(psKey);
            break;
        case DescValueType.STRINGTYPE:
            return desc.getString(psKey);
            break;
        case  DescValueType.OBJECTTYPE:
            return desc.getObjectValue(psKey);
            break;
        case  DescValueType.LISTTYPE:
            return desc.getList(psKey);
            break;
        case  DescValueType.ENUMERATEDTYPE:
            return desc.getEnumerationValue(psKey);
            break;
    }
};
var channelCount = app.activeDocument.channels.length;
var channelNames = [];
for(var channelIndex=1;channelIndex<=channelCount;channelIndex++){
    channelNames.push(getProperty(charIDToTypeID("Chnl"),charIDToTypeID("ChnN"),channelIndex));
}
alert(channelNames);

[Daikazu]

Thanks for your Help Michael. I have things running much faster now.