Best way to place lots of images into one

Question

Hello,
I have made a Javascript script that loops between 20.000+ images and puts them into a main image. Code is:
var sampleDocToOpen = File('~/a/'+(l+startF)+'/'+(i+start)+'.png')
open (sampleDocToOpen)
app.activeDocument.selection.selectAll()
app.activeDocument.selection.copy()
app.activeDocument.close()
app.documents[0]
app.activeDocument.paste()
it works, but it is extremely slow (I also have the main image flattened every 30-40 images to make it quicker).
So i tried to place the images directly into the main image via:
function placeFile(file) {
     var desc = new ActionDescriptor();
     desc.putPath( charIDToTypeID('null'), file );
     desc.putEnumerated( charIDToTypeID('FTcs'), charIDToTypeID('QCSt'), charIDToTypeID('Qcsa') );
         var offsetDesc = new ActionDescriptor();
         offsetDesc.putUnitDouble( charIDToTypeID('Hrzn'), charIDToTypeID('#Pxl'), 0.000000 );
         offsetDesc.putUnitDouble( charIDToTypeID('Vrtc'), charIDToTypeID('#Pxl'), 0.000000 );
     desc.putObject( charIDToTypeID('Ofst'), charIDToTypeID('Ofst'), offsetDesc );
     executeAction( charIDToTypeID('Plc '), desc, DialogModes.NO );
But after opening few images it says that "scratch disks are full", and I verify that it is true since almost 500GB of the HD are used by the application... Images are 512x512 each, thus the resulting image main image is 83456x63488.
Is there a faster way I could try to use??
Thanks a lot!

Answer 1

And also realize what is going on. First your using a script. Though a script is a program with logic its source code which is not compiled into machine code its has to be intrepided into machine executable code as the script processor  iterate through your buffered source code. This itself takes time. Then you have to understand what is happening in your loop and what Photoshop has to do once the Script code can be executed.  Using Copy and Paste or Place requires Photoshop to open and read in 20,000 encoded jpeg images files and one way or the other decode the encoded image for rendering to copy it to the Clipboard  or render the embedded smart object copy into the Smart Object Layer. Then there is the other code that you have to add canvas and distribute the images layers across the canvas. Intrepiding the script source code some 20,0000 times is something like doing 20,000 compiles where the source code is only read in once but is turned into machine executable code 20,0000 times.  To process 20,000 encoded images files using a full feature image Editor program and a scripting process is going to take a long tome and require a lot of machine resources.  If you want a fast solution you will need custom compiled program designed for your process. Still reading and decoding 20,000 small jpeg image files is going to take some time and require quite a bit of machine resources. It might be better to use an image file format that doesn't use compression and complex image encoding to cut down on the amount of processing reqruired .