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Author Topic: file problem  (Read 3483 times)

Offline spinner

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file problem
« on: April 29, 2011, 07:33:28 PM »
This might be a Mac problem more than a Photoshop. I found an old GIF file on a floppy disk. Was a scan from the 90's a picture of myself from another life.  Anyway I was trying to clean it up with Photoshop on the Mac. Got some work done and saved it as a .JPG. Because I have a plug in on my PC for Photoshop that doesn't have a Mac equivilent I tried to open that .jpg using Elements on the PC. It wouldn't open saying the file had an unknown or invalid JPEG marker.


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Offline Oldboy

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Re: file problem
« Reply #1 on: April 29, 2011, 09:34:43 PM »
When you save it on the Mac you need to save as a PC file otherwise, the PC can't open the file. See video below.  ;D

http://www.youtube.com/watch?v=nLJj4y28l68

Offline spinner

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Re: file problem
« Reply #2 on: April 30, 2011, 01:02:00 AM »
I thought the various photo files were universal? A jpeg is a jpeg is a jpeg. I don't have any issues with jpegs that I've edited on a Linux box with GIMP. I can open them with either the PC or the Mac without any issues. BTW that link is showing someone how to network a Mac and a PC. Oh, and the original GIF was on a PC and transferred to the Mac without issue.
« Last Edit: April 30, 2011, 01:03:36 AM by spinner »
And more, much more than this, I did it my way
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picsfor

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Re: file problem
« Reply #3 on: April 30, 2011, 07:22:22 AM »
Split on this, as i don't think we have enough info.
There is the option that you had a corrupt file save, as it is possible that you used a save as option that is not necessarily compatible. It isn't jpg's that are the issue - more over the data structure used to save the jpg (in other words not a FAT or NTFS file structure).

M$ Windows doesn't by nature, read Mac OS stuff, where as Apple can read MS stuff...

Offline Oldboy

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Re: file problem
« Reply #4 on: April 30, 2011, 08:16:40 AM »
I thought the various photo files were universal? A jpeg is a jpeg is a jpeg. I don't have any issues with jpegs that I've edited on a Linux box with GIMP. I can open them with either the PC or the Mac without any issues. BTW that link is showing someone how to network a Mac and a PC. Oh, and the original GIF was on a PC and transferred to the Mac without issue.

Sorry, I thought it showed how to save a file on the Mac so a PC could access it.  :-[

As picsfor says, a Mac can read a PC file but the PC can't read a Mac file unless, it's saved as a PC file structure. So, transferring the Gif from a PC to the Mac isn't a problem, but saving on the Mac after working on the file, changes the structure format of the file hence, why you can't open it on the PC. When saving on the Mac you can change the file structure so it can be opened on a PC. Have posted another link below.  ;D

http://www.ehow.com/how_6907549_do-photoshop-jpg-pc-jpg_.html

Offline Jonathan

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Re: file problem
« Reply #5 on: April 30, 2011, 03:54:59 PM »
I thought the various photo files were universal? A jpeg is a jpeg is a jpeg.

That's true.  There is no such thing as a "Mac jpeg" or a "Windows jpeg" - it's a jpeg.  Somehow your file is corrupt.

From what you say the most likely cause is that you didn't really save it as a jpeg - you saved it as something else (maybe a gif?) with a jpeg extension.  Macs don't (always) use the extension to work out the file type but PCs do.  PCs will throw a wobbly trying to open something called a jpeg that isn't but Macs will just generally get on with it.

If it's not that then the file is corrupt for some other reason.

As picsfor says, a Mac can read a PC file but the PC can't read a Mac file unless, it's saved as a PC file structure. So, transferring the Gif from a PC to the Mac isn't a problem, but saving on the Mac after working on the file, changes the structure format of the file hence, why you can't open it on the PC. When saving on the Mac you can change the file structure so it can be opened on a PC. Have posted another link below.

Nope.  You're confusing disk formats with file formats.

PCs can read and write NTFS and FAT.  Older Macs can read and write HFS and FAT and read but not write NTFS.  Recent Macs can read and write NTFS too (I think it came in in Leopard but it may be new in Snow Leopard).  PCs may be able to read HFS now.  They might even be able to write it for all I know.  But that doesn't affect the file format - if the OS can read the disk it should be able to read the file.
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Offline spinner

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Re: file problem
« Reply #6 on: April 30, 2011, 08:13:06 PM »
Well I had go out to my garage to find it, but i fired up an old Linux box and added it to my home network and grabbed the file off the Mac with GIMP and it opened no problem. I'm starting to wonder if my Win 7 doesn't network properly as I had issues printing Word doc.'s from the Mac to a printer networked from that same Win 7.

You triggered a memory Jonathan, I recall on one of my computer courses being told that it's not just the ext. that makes the file, there is a block of code at the very front of every file that identifies it and sets up which program it should work with, so you are probably right in that the Mac writes that block differently and Windows can't read it.
And more, much more than this, I did it my way
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Offline spinner

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Re: file problem
« Reply #7 on: May 02, 2011, 02:54:01 AM »
There's definitely something strange occurring between my Mac and my Win7 PC. I've just opened up the file with my HP lappy running Win7 without any problems.  Some kind of networking issue it seems.
And more, much more than this, I did it my way
Ol' blue eyes

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Offline Jonathan

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Re: file problem
« Reply #8 on: May 02, 2011, 08:25:53 AM »
Go to the file on the Mac, hit Apple-I and tell me what it says under "Kind" ( in the general section).

My guess is still that it isn't a jpeg.

Macs identify file type by looking at the file type setting in the resource fork.  If there's none present then they guess based on the extension.  I assume Linux does the same (since they are both essentially derivates of Unix). 

That might also explain why a Win7 box could open it - assuming M$ had finally changed to match *nix systems.
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picsfor

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Re: file problem
« Reply #9 on: May 02, 2011, 09:47:34 AM »
To my knowledge, M$ is still built to accommodate the old DR DOS legacy.

Until they take the decision to move back to the Unix family, they will always have these issues. That is one of the reasons i chose to move away from M$ - the incompatibility with the rest of the world...

Offline Hinfrance

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Re: file problem
« Reply #10 on: May 02, 2011, 10:28:24 AM »
To my knowledge, M$ is still built to accommodate the old DR DOS legacy.

Until they take the decision to move back to the Unix family, they will always have these issues. That is one of the reasons i chose to move away from M$ - the incompatibility with the rest of the world...

Is that the 11% of the world that doesn't use MS?  :2funny:  :2funny:
 
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Offline Oldboy

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Re: file problem
« Reply #11 on: May 02, 2011, 12:06:00 PM »
To my knowledge, M$ is still built to accommodate the old DR DOS legacy.

Until they take the decision to move back to the Unix family, they will always have these issues. That is one of the reasons i chose to move away from M$ - the incompatibility with the rest of the world...

Is that the 11% of the world that doesn't use MS?  :2funny:  :2funny:
 
Sorry Andy, couldn't resist it . . .

 :2funny: :2funny:

picsfor

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Re: file problem
« Reply #12 on: May 02, 2011, 02:07:25 PM »
Your point is well made and i did open myself up for that...  :-X

That said, M$ is slowly ceasing to be the main O/S as the world moves towards mobile computing with tablets and phones.
People are just so fed up with the issues associated with M$ that they just want simple and reliable computing, and M$ is not it.
Not saying Apple is the promised land - but Unix based systems are...

Offline spinner

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Re: file problem
« Reply #13 on: May 03, 2011, 01:51:45 AM »
Go to the file on the Mac, hit Apple-I and tell me what it says under "Kind" ( in the general section).

My guess is still that it isn't a jpeg.

Macs identify file type by looking at the file type setting in the resource fork.  If there's none present then they guess based on the extension.  I assume Linux does the same (since they are both essentially derivates of Unix). 

That might also explain why a Win7 box could open it - assuming M$ had finally changed to match *nix systems.

Apple i says "JPEG image". Name extension says " Dav copy.jpg". However, if I use Windows Explorer on the PC in question and browse the Mac it identifies the file as
"._dav copy.jpg". In fact I've noticed that going back to Christmas, every file that was
worked on is preceded with "._". I've check with my HP lappy and my daughter's PC which networked with the others and both see "dav copy.jpg" and can open the file no issue.

Given the problem I have had trying to get the Mac to print on a networked printer attached to the same Win7 machine I'm convinced something is getting garbled during the packet transmissions between these two specific machines.
And more, much more than this, I did it my way
Ol' blue eyes

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https://www.flickr.com/photos/spin498/

Offline Jonathan

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Re: file problem
« Reply #14 on: May 03, 2011, 08:38:12 AM »
Woah!!!!!!

Let me guess, are the files on the PC fairly small and pretty much all the same size?

That's not the file itself (aka the data fork) - that's the resource fork.

Looks like when you copy the file to the PC you are picking up the resource fork not the data fork and PCs don't like those at all.  The file name starts with a . which in Unix says "hide this file". 
This is a guess (because it's beyond my current PC knowledge) but does the "problem" machine have "show hidden files" turned on and the other have it turned off?  If so then turn it off.

Either way, it's generally safer pushing files from Mac to PC than pulling them from PC to Mac (since Mac understands its own file structure)
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