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Geoff Tani
24 August 2006, 02:26 AM
Like many of you, I have been digitizing my old family photographs. Following the advice of people on ReunionTalk and others, I have scanned the photographs to high resolution TIF or PSD files. Those files are the "masters," and from them I create jpg copies, which I use in Reunion, in iPhoto, on the web, etc. The masters go to an archive HD; the jpgs are for publication.

I don't know much about digital images, but I've read on ReunionTalk, and been told by people, that every time you modify something in a digital image, and then save the file, the image degenerates a little. So if you rotate the image and save, it degenerates a little; if you adjust the histogram to lighten or darken it and save, it degenerates a little. Maybe the degeneration is practically invisible to the human eye, since I can't tell anything by just looking at the before and after.

Assuming that this is true, I have never touched the master files. But there are thousands of master files. Many images are upside down or on their sides (so they must be rotated); many are not in the center of the canvas (so they must be trimmed); many have awful light & contrast levels (so they need to adjusted).

But I leave the masters as is, and instead modify only the jpgs. The results are good, but the process is super labor intensive. And if I want to create a new set of jpgs (for example with a different dpi), I have to start all over: copy to jpg, rotate, trim, straighten, add a nice border, adjust levels,...

Sorry about the long-winded background. Here are my questions:

1. Am I correct in assuming that every time you modify something in an image and save, that the image does degenerate? By how much? Enough to really worry about, or not? Does this degeneration happen with all image formats, or just with compression formats like jpg? IE, does degeneration NOT happen with TIF and PSD?

2. Are there some modifications that cause either zero or negligible degeneration? I would like take the TIF and PSD masters, do the following, and save them:
- rotate them to the correct orientation
- trim out the background up to the edge of the photograph (the background is also WITHIN the canvas)
- straighten the image as needed
- adjust levels for really dark or light images

Which, if any, of the above actions cause degeneration? Is it better to not modify the masters at all, or is the above amount of modification OK?

All advice welcome. Thanks a lot.

theKiwi
24 August 2006, 07:36 AM
1. Am I correct in assuming that every time you modify something in an image and save, that the image does degenerate? By how much? Enough to really worry about, or not? Does this degeneration happen with all image formats, or just with compression formats like jpg? IE, does degeneration NOT happen with TIF and PSD?
The "degeneration" is a function of the file format used to save the file. The JPEG format is what most people refer to when they're talking about loss of image quality each time the file is opened and saved, since each time the file is saved it's evaluated to see what data can be thrown away in order to make the file size smaller. Formats like TIFF and PSD save all the data, and PSD saves the Layers information if you use Layers at all.

2. Are there some modifications that cause either zero or negligible degeneration? I would like take the TIF and PSD masters, do the following, and save them:
- rotate them to the correct orientation
- trim out the background up to the edge of the photograph (the background is also WITHIN the canvas)
- straighten the image as needed
- adjust levels for really dark or light images

As long as you save the file back as an uncompressed TIFF file, or as long as you're comfortable with your future ability to open .psd files probably even better as .psd files, then there will be no degeneration. Just leave the master files to be the ones that contain the maximum amount of information you have after you've made the adjustments you're talking about above, and anytime you need a fresh image for web, or a calendar, or an iPhoto book etc etc, start from the master again.

The steps you mention above in 2 are what I do at the scanning stage for each image before I first ever save the file.

Hope this Helps

Roger

marnen
24 August 2006, 03:45 PM
Like many of you, I have been digitizing my old family photographs. Following the advice of people on ReunionTalk and others, I have scanned the photographs to high resolution TIF or PSD files. Those files are the "masters," and from them I create jpg copies, which I use in Reunion, in iPhoto, on the web, etc. The masters go to an archive HD; the jpgs are for publication.

I don't know much about digital images, but I've read on ReunionTalk, and been told by people, that every time you modify something in a digital image, and then save the file, the image degenerates a little.

To amplify Roger's response, if you're working on TIFF or Photoshop files (or indeed any format other than JPEG), you're fine -- there is no degeneration in these formats. What I would advise, then, is to do all your editing in some non-JPEG format (Photoshop is one obvious choice). If you need a JPEG image, then just export to JPEG format when you've got an image you like.

Bill McQuary
25 August 2006, 11:48 AM
Which, if any, of the above actions cause degeneration? Is it better to not modify the masters at all, or is the above amount of modification OK?

All advice welcome. Thanks a lot.

Tani,

Professional photographers archive their master images and you may want to adopt that practice. The first thing they do after a shooting session is to download all the images to their computer and burn a CD of them. This is done prior to any image editing.

After a scanning session you might do the same thing before you trim, rotate, straigten or crop any of your scans using Photoshop, iPhoto or another editor.

BTW, if your scans are in PSD or TIF format, little if any image degradation will result. But your project time will be reduced if you adopt a work flow that initially archives your scans on CD and then use those CDs as a source of the images you edit.

Hope this Helps.
Bill

marnen
25 August 2006, 11:59 AM
BTW, if your scans are in PSD or TIF format, little if any image degradation will result.

Not "little if any". None. Because of the nature of these file formats, degradation simply cannot happen.

(Caveat: there are a lot of variants of TIFF. It's possible that one of them uses JPEG-style compression, but I've never heard of this in actual practice. Ever.)

But your project time will be reduced if you adopt a work flow that initially archives your scans on CD and then use those CDs as a source of the images you edit.

It's probably a good idea, but it won't reduce project time. CDs are slower than hard drives.

Bruce Jones
31 August 2006, 03:23 AM
I'm a graphic designer and have been using Photoshop to preserve my family fotos for years. The larger file size you can scan in at, the better the overall look. One thing I do is increase my canvas size (in photoshop) to include a white area under the photo. While in photoshop, I add a type layer that identifies the people, gives the place and date the photo was taken. Too many times the photos have information on the back of them and that is lost. This gives everyone as much information as possible.

marnen
31 August 2006, 05:43 PM
Clever. Some image formats -- notably JPEG -- also support storing metadata in a supplementary record in the file. See http://www.exif.org/ .

Geoff Tani
10 September 2006, 08:05 PM
Thanks, everyone, for the advice. As always, it is tremendously helpful.

May I ask some follow up questions?

1. I take a picture with a digital camera and save it as jpg. (My camera does not save as RAW or tif.) Then I open the image in Photoshop, crop & rotate it, and save as tif or psd. Is there any degeneration then? In this case, which image should I archive as the master image -- the jpg, or the tif/psd?

2. What if I cut out a section of a larger image, then enlarge the print size of the cut-out to that of the original image?

Example: In Photoshop I open a tif or psd image, which is 600 dpi with a print size of 8x10. However, I only want a part of it which takes up 1/4 of the image. So I select that 1/4 part and delete the rest, then resave. Then I set the print size of the newly saved image as 8x10. Is there any degredation here, since I have stretched out 1/4 to print at 8/10? Should I NOT enlarge the print size of the newly saved image, but instead just leave it as is?

theKiwi
10 September 2006, 10:02 PM
1. I take a picture with a digital camera and save it as jpg. (My camera does not save as RAW or tif.) Then I open the image in Photoshop, crop & rotate it, and save as tif or psd. Is there any degeneration then?

None that is avoidable. I'd probably open it in Photoshop, then do the Save As to get it to TIFF or .psd before doing the rotate and anything else on it.

In this case, which image should I archive as the master image -- the jpg, or the tif/psd?

I'd do as much to the image as is non-destructive and then save that as .psd or TIFF to be the master file. Eg if you've taken a digital picture of an olde photograph or slide with a slide copier, and you need to crop it to remove the frame, or rotate it slightly to get it squared up, I'd do that before saving the master image, otherwise you'd need to do that every time you want to start from the master image again.

But I wouldn't crop all of the background and the dog out of the picture before saving the master image.

2. What if I cut out a section of a larger image, then enlarge the print size of the cut-out to that of the original image?

Example: In Photoshop I open a tif or psd image, which is 600 dpi with a print size of 8x10. However, I only want a part of it which takes up 1/4 of the image. So I select that 1/4 part and delete the rest, then resave. Then I set the print size of the newly saved image as 8x10. Is there any degredation here, since I have stretched out 1/4 to print at 8/10? Should I NOT enlarge the print size of the newly saved image, but instead just leave it as is?

First of all resave should be another Save As to a different file name yet again....

If you have some reason to need only a portion of it, but have it printed at 10x8, then do as you suggest above, but if you're not going to actually print it out at 10 x 8, then just leave it at whatever pixels you ended up with after the crop operation - in your example the picture at 600 dpi is going to be 6000 pixels by 4800 pixels. If you crop that to the centre 1/4, you'd have 1500 pixels by 1200 pixels.

Photoshop would now show the image size as being 2 1/2 inches by 2 inches, which is only important if you're then going to actually print it out of Photoshop. The main thing is you have 1500 x 1200 pixels, and you can print that at whatever size you want to - that would print at 10 x 8 if you changed the resolution to 150 dpi, or if you told Photoshop to print it at 400%.

There is no benefit to increasing the print size if you leave the pixel size the same.

Roger

AE Palmer
11 September 2006, 08:30 PM
May I ask some follow up questions?

1. I take a picture with a digital camera and save it as jpg. (My camera does not save as RAW or tif.) Then I open the image in Photoshop, crop & rotate it, and save as tif or psd. Is there any degeneration then? In this case, which image should I archive as the master image -- the jpg, or the tif/psd?

Just because the camera saves pictures in .jpg format does not mean you should retain that format after the image has been created. The very first thing you should do when opening a .jpg in Photoshop, is to save it is some other format - preferably .psd. Once that is done, you can make modifications without pixel data loss. However, most people will create a "Master" file that has no changes made whatsoever. If changes are nereded, a Save As copy is made and modifications are made on THAT file.

Once an image has been saved in a lossless format (i.e.: .psd or .tif), you can make as many modifications as you like without losing pixel data.

To answer your question more specifically: you should save a master copy in .psd or .tif format without modifications. Then make a second copy and make modifications on the copy. As a personal preference, I never preserve master images in .jpg format.

marnen
12 September 2006, 01:14 AM
Since no one quite gave a clear answer...
1. I take a picture with a digital camera and save it as jpg. (My camera does not save as RAW or tif.) Then I open the image in Photoshop, crop & rotate it, and save as tif or psd. Is there any degeneration then?
No. Photoshop will get all it can out of the JPEG file, then save that information essentially unaltered into the TIFF/PSD file. Both of these formats are lossless.
In this case, which image should I archive as the master image -- the jpg, or the tif/psd?
Probaby the one in the lossless format.

Geoff Tani
18 November 2006, 02:27 AM
Thanks again to everyone for their helpful advice. Sorry to reopen this thread, but I have noticed the following:

I take a TIF file with a file size of 33MB. I open it in Photoshop and, without modifying it at all, save it as PSD. The new PSD file is 2MB. In disbelief that PSD, a lossless format similar to TIF, can cause the file size to shrink that much, I open both files and compare them. The resolution is the same. Zoomed in to 100%, they look exactly the same. I take the PSD file and save it as TIF. This second TIF file is 33MB, just like the first.

I'm still in disbelief. Can you really take a 33MB TIF, save it to a 2MB PSD and still not have any loss of image information? (If the answer is yes, then I can save a lot of disk space!)

If you take a TIF file, save it as PSD, then save that PSD to TIF, does the second TIF file contain the same image information as the first TIF? (When I do this TIF-PSD-TIF exercise, the byte counts for the two TIF files are about about 1KB different.)

theKiwi
18 November 2006, 08:13 AM
I'm still in disbelief. Can you really take a 33MB TIF, save it to a 2MB PSD and still not have any loss of image information? (If the answer is yes, then I can save a lot of disk space!)

If you take a TIF file, save it as PSD, then save that PSD to TIF, does the second TIF file contain the same image information as the first TIF? (When I do this TIF-PSD-TIF exercise, the byte counts for the two TIF files are about about 1KB different.)

If you use compression in the TIFF file you could likely make it quite a bit smaller.

There are two types of compression - lossless where nothing is discarded, and lossy where some stuff is discarded, with how much stuff is discarded depending on what degree of compression you apply - the more you compress the file the more is thrown out.

TIFF files can be compressed with a lossless compression called LZW, and Photoshop uses its own methods of storing data in the file.

More than you ever wanted to know can be found here (with all the links on the page too)

http://en.wikipedia.org/wiki/Image_compression

Cheers

Roger

marnen
18 November 2006, 07:45 PM
Yes, it's possible. Efficient file formats can be amazing things. Just as an example, I recently created a 500K XML file that, after lossless compression with gzip, was only 1K!

Tom Robinson
20 November 2006, 07:27 PM
TIFF files can be compressed with a lossless compression called LZW, and Photoshop uses its own methods of storing data in the file.

To expand:

TIFF files can be compressed or uncompressed. If they're compressed, it's always lossless compression.

In GraphicConverter, this is an option when you do a Save As: click on the Options button and you'll see more compression (and other) options than you wanted to know about. The two to experiment with are LZW and LZW with Prediction--try a couple of images in both formats and see what the size reduces too.

There may still be minor size differences between a well compressed TIFF and a PSD file, but personally I'd always use TIFF: PSD files are proprietary, and TIFF is the more widely supported standard.