Dividing big document to smaller ones

I'am working on a 1x20m banner

What are the resolution and bit depth?

This Script should split a file into segments, but I am not sure this will be necessary.

// split image into x times y segments and save them as psds;

// 2017, use it at your own risk;

#target photoshop

if (app.documents.length > 0) {

var originalUnits = app.preferences.rulerUnits;

app.preferences.rulerUnits = Units.PIXELS;

// document;

var myDocument = app.activeDocument;

var theName= myDocument.name.match(/(.*)\.[^\.]+$/)[1];

var thePath = myDocument.path;

var theCopy = myDocument.duplicate("copy", false);

// the numbers;

var theX = 2;

var theY = 2;

var xFrac = myDocument.width/theX;

var yFrac = myDocument.height/theY;

// psd options;

psdOpts = new PhotoshopSaveOptions();

psdOpts.embedColorProfile = true;

psdOpts.alphaChannels = true;

psdOpts.layers = true;

psdOpts.spotColors = true;

// create folder;

var folderName = thePath+"/"+theName+"_"+theX+"x"+theY;

if (Folder(folderName).exists == false) {Folder(folderName).create()};

//save jpgs;

for (var n = 1; n <= theY; n++) {

for (var m = 1; m <= theX; m++) {

cropTo((m-1)*xFrac, (n-1)*yFrac, m*xFrac, n*yFrac);

var theNewName = theName+"_"+bufferNumberWithZeros(m, 3)+"_"+bufferNumberWithZeros(n, 3);

theCopy.saveAs((new File(folderName+"/"+"_"+theNewName+".psd")),psdOpts,true);

theCopy.activeHistoryState = theCopy.historyStates[0];

}

};

theCopy.close(SaveOptions.DONOTSAVECHANGES);

// reset;

app.preferences.rulerUnits = originalUnits;

};

////// buffer number with zeros //////

function bufferNumberWithZeros (number, places) {

var theNumberString = String(number);

for (var o = 0; o < (places - String(number).length); o++) {

theNumberString = String("0" + theNumberString)

};

return theNumberString

};

////// crop //////

function cropTo (x1, y1, x2, y2) {

// =======================================================

    var desc7 = new ActionDescriptor();

        var desc8 = new ActionDescriptor();

        var idPxl = charIDToTypeID( "#Pxl" );

        desc8.putUnitDouble( charIDToTypeID( "Top " ), idPxl, y1 );

        desc8.putUnitDouble( charIDToTypeID( "Left" ), idPxl, x1);

        desc8.putUnitDouble( charIDToTypeID( "Btom" ), idPxl, y2 );

        desc8.putUnitDouble( charIDToTypeID( "Rght" ), idPxl, x2 );

    var idRctn = charIDToTypeID( "Rctn" );

    desc7.putObject( charIDToTypeID( "T   " ), idRctn, desc8 );

    desc7.putUnitDouble( charIDToTypeID( "Angl" ), charIDToTypeID( "#Ang" ), 0.000000 );

    desc7.putBoolean( charIDToTypeID( "Dlt " ), false );

    desc7.putEnumerated( stringIDToTypeID( "cropAspectRatioModeKey" ), stringIDToTypeID( "cropAspectRatioModeClass" ), stringIDToTypeID( "pureAspectRatio" ) );

    desc7.putBoolean( charIDToTypeID( "CnsP" ), false );

executeAction( charIDToTypeID( "Crop" ), desc7, DialogModes.NO );

};

You might get away with an even lower resolution.

What print resolution works for what viewing distance?

25 - 30 ppi should normally be enough for this.

People always overestimate the ppi requirements for large scale printing. Worst case, they've been told "300ppi" as if that was some universal law of nature.

Generally, anything above 15000 pixels long side is probably more than you need.

Nothing wrong as such, as long as your system can handle it. But it may be completely wasted.

Seen from a couple of meters away, there's no way the eye can resolve, say, 72 individual pixels to an inch. You don't have to step back much before an inch gets really small.

This really boils down to degrees of arc in your total field of vision.

The files get bigger and that can affect Photoshop’s performance so one sometimes has to weigh the benefits against the disadvantages.

In any case I would recommend employing non-destructive techniques, in particular Smart Objects, so that pixel elements maintain whatever resolution they may have beyond what’s currently being utilised as much as possible.