Script to show JPEG degradation

Question

Hello All,
I'm trying to demonstrate the degradation of jpeg's over multiple recompressions.
My planned approach is;
Open image;
Save image as new file at compression rate x;
Open the newly compressed file;
Loop;
I would like to run the script so I get 1000 images in a folder each x% of the previous image.
Does that make any sense?
If anyone has any ideas to help me i'd very much appreciate it.
tia
fess

Answer 1

Hi, sorry to be a pain.
I've had a go at adjusting the code;
// saves jpg multiple times;
// be advised: this closes the open file without saving and overwrites existing jpgs of the same name without prompting.
// 2011, use it at your own risk;
#target photoshop;
// set the number of saves;
var theNumber = 1000;
if (app.documents.length > 0) {
var thedoc = app.activeDocument;
// getting the name and location;
var docName = thedoc.name;
if (docName.indexOf(".") != -1) {var basename = docName.match(/(.*)\.[^\.]+$/)[1]}
else {var basename = docName};
// getting the location, if unsaved save to desktop;
try {var docPath = thedoc.path
     var thePath = docPath+"/"+basename+".jpg";
catch (e) {
     var docPath = "~/Desktop";
     var thePath = docPath+"/"+basename+".jpg";    
// save as jpg if not a jpg yet;
if (docName.indexOf(".jpg") == -1) {
// jpg options;
     var jpegOptions = new JPEGSaveOptions();
     jpegOptions.quality = 0;
     jpegOptions.embedColorProfile = true;
     jpegOptions.matte = MatteType.NONE;
//save jpg as a copy:
     thedoc.saveAs((new File(thePath)),jpegOptions,true);
// close doc;
thedoc.close(SaveOptions.DONOTSAVECHANGES);
//save jpg as a copy:
for (var m = 0; m < theNumber; m++) {
     File(thePath).copy(File(docPath+"/"+basename+"_"+bufferNumberWithZeros(m + 1, 3)+".jpg"));
     var thePath = docPath+"/"+basename+"_"+bufferNumberWithZeros(m + 1, 3)+".jpg";
     var thedoc = app.open(File(thePath));
// make change;
     thedoc.selection.selectAll();
     thedoc.selection.invert();
     thedoc.selection.selectAll();
     thedoc.selection.invert();
// save;
     thedoc.save();
     thedoc.close(SaveOptions.DONOTSAVECHANGES);
//that’s it; thanks to xbytor;
////// 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
When I run this code cs4 brings up a warning saying 'no pixels have been selected'. There is a check box to ignore future warnings. I assume it's my code?
I don't think I need the second selectAll but i'm not sure.
Am I being dense?
thanks once again