Photoshop, JPEG format, lotsa pixels - limitation?

Factual Questions
1

I was using Photoshop to join together some already-massive image files, saving as I successfully added each new segment, enlarging the canvas size on an as-needed basis. I was saving the file in JPEG format – the image is a map made up of a small handful of colors and on the PowerBook I’ve got more processor oomph to spare than disk space, so I figured “yeah, compress the hell out of it and store it small”.

During Take I of this little project, I realized for the nth time that I needed a bigger canvas to encompass the next set of map fragments, so I upped the canvas size to 11000 x 18000, copied new fragments, pasted, lined up, edited edges, saved. Quit for lunch. Reopened file, and when it came up there was nothing in it but a single black vertical line about 15 pixels wide. :frowning:

So I’m thinking to myself, OK, random corruption, and I was stupid to have not made intermittent backups as I went. Begin Take II of this project. This time, once I had worked from the map fragment I knew to be maximum north (therefore top of final image file) and the one I knew to be maximum west (therefore far left of image file), I went ahead and enlarged the canvas to the final necessary size of 11000 x 18000 pixels, thinking to myself “It was obviously random corruption last time but just in case, I’ll close and reopen the file after it finishes saving”. This time I got about 17 randomly colored perfectly parallel vertical lines of about 5 pixels each. ??!!??

Duplicated and then opened one copy of the backup I’d made just before doing the canvas expansion (yeah I learn) and did it again, this time saving the file in native Photoshop format. Close file. Open file. Hey, still a map! (and smaller than I’d expected, only 20 MB in Photoshop format)

OK…so either Photoshop (at least my elderly version of it) lacks something it needs to save a file that large as a JPEG, or the JPEG format itself runs out of something-or-other at some point.

(I know it isn’t a failure of Photoshop 3.0 (I said it was an elderly version) to READ a JPEG that size, because I copied the file to one of the graphics folks’ G4s with a gig of RAM and went at it with their copy of Photoshop 6 and saw the same results as on my own machine.)

Anyone care to venture an hypothesis?

::sees hand raised in back, points::

No, as a matter of fact I’m NOT going to upload it and give you the URL!!!

2

No specific answer and I am not familar with MACS (big help so far eh?) but having dealt with huge Photoshop files in the recent past I can attest to the fact that a lot of weirdness goes on in trying to stitch together giant files and you can actually bump into some unexpected OS and program coding limitations/bugs/features! as the file is read out prior to compression, especially with the older versions. I would suggest upgrading to Photoshop 6 (or current MAC equivalent) I have 5.5 for Windows and it handles huge files fine.

Ebay is a good place to look for deals on Photoshop.

3

Could the ultra high compression be partly to blame? JPG is lossy compression, you give up image information for a smaller file size.

4

Never mind (blush) read the end of your OP again. Sorry for useless post. Getting late.

5

AH,

In all honesty, I use Picture Publisher (by Micrografix) to compress jpeg files. Neither Photoshop nor Paint Shop Pro can adequately compress a file for crap, IMHO.

I use Photoshop 6.0 now…it’s much better than previous versions but still doesn’t give me the output I desire.

If it’s a work project I suspect you need to keep those files as large as possible if it’s for print. If it’s for the web…screw it, it’s too damn big anyway and not worth your time.

6

This probably isn’t the cause of your problem, but you shouldn’t use jpeg as an intermediate format, because you will lose information whenever you save and re-open the file.

7

Just how limited are you in disk space, here? Maybe you’ll want to do this particular project in an uncompressed format… or maybe lower the amount of compression you do to it.

Oh, and also… 11000X18000? Da-a-a-a-a-a-a-a-amn… you have my pity.

8

Photoshop 3? Man, that’s sad! :wink: Come on! Go out and get Photoshop 5 LE, at the very least! Or Photoshop Elements - I hear it gives a great deal for the buck! I have Photoshop 6 on my Mac, but I have never done the…well…rather odd thing you were doing on it! (Sorry, I’m clueless - I’m a web graphic kind of girl.)

I will repeat Manduck: that re-saving and re-saving in the jpeg format probably isn’t a good idea. All that re-compressing doesn’t sound good. I’d imagine it would be worse if you close the file, and then re-open it. Especially with Photoshop 3. I think Photoshop 6 handles this better.

P.S.: Oh, and just so you know, if you want to upgrade to PS 6 using your PS 3 CD? Can’t. Adobe needs a Photoshop 4 or higher CD in your hot little hands (and in your CD drive) in order to “confirm” that you are eligible for an upgrade. I don’t know if you already know this, but I’m floating that information out there for anyone who doesn’t know. It wasn’t common knowledge to me when I upgraded. (Luckily I was upgrading from PS 5.5.)

9

There were huge bugs in the jpeg routines in PS3. Some third-party plugins were available that didn’t have these problems. Back in the ancient days of PS3, most of us used the 3rd party jpeg plugs due to the very bug you are describing.
But you really shouldn’t be saving intermediate workfiles in jpeg format, or any lossy format for that matter. Subsequent resaves will recompress the data and it will gradually degrade due to jpeg artifacts. Save them as PS files, the compression is not too bad, and not lossy. Disk space is cheap. Your time recreating lost work is expensive.

10

…And even when you do save the final product, for your purposes (regions of one of a small number of possible colors), GIF will probably be more efficient than JPEG.