Will JPEG files suffer a quality loss in these situations??

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rongrover
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Joined: Jun 1 2002

I have just spent most of today putting my SM Cards onto CD's. (some of you may recall that I have never done this before as I always kept the Cards and I have thousands of photos)

Obviously the Card holds the original file and so as I see it, the CD's now have a file without any loss in quality from the JPEG originals.

However, I have put some onto CD from Files held on the computer and I am wondering if this now means that those files will experience a drop in quality as JPEG files do each time they are copied.

I feel that the process of burning may not bring about a file quality reduction, but when I told someone what I was doing, they said that they thought it would.

I also thought I noticed that when I was transfering the larger 6million pixel files in best quality (a file size of about 17MB each photo) that they were in TIFF and not JPEG. If this is so, at what point does the file on the camera produce a TIFF as against JPEG?

Although I have been doing Digital Photo work for quite some time, I really am not sure about the above points.

Any advice please, Ron.

PaulD
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Joined: Aug 31 2002

Hi
If you copy a file from a flash card or from a hard drive to a CD-R, the copy is absolutely digitally identical, so if it is a JPEG then the opriginal and copy will look the same.when opened in a viewing application, or printed.

A digital camera will have some sort of menu setting that deals with saving photos as either Tiffs or JPEGs - or if it is a cheaper camera it will be unselectable, but the manual should explain what compression the camera is applying to reduce the file sizes.

If you open a JPEG in an image editing program, then resave it at the same level of compression, then you are probably slightly degrading it, especially if you do this repeatedly. If you resave it as an uncompressed bitmap then no further degradation will be occurring.

If you are concerned about reducing the size of your Tiff files for storage, there are options in resaving a Tiff file to apply lossless compression.

For more compression you could resave the Tiffs as JPEGs - at the Photoshop 100% quality setting I cannot see any difference between an uncompressed image and the JPEG (magnifying it to compare), but the file size is considerably smaller.
Regards

[This message has been edited by PaulD (edited 15 January 2004).]

rongrover
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Joined: Jun 1 2002

Thanks Paul, you have confirmed what I thought.

When working on a photo I do this in Photoshop and there I would usually work in their format.

What I think my friend was refering to is if you keep your phots in JPEG and work on them and save again in JPEG, when you reopen the file it will have lost some quality.

Thanks again, Ron.

Alan Roberts at work
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Joined: May 6 1999

Yes, that's exactly right. If you create JPEG in the camera and just copy it to CD, there can be no change of content or quality. If you decode it and recode it, there may well be a quality drop. If you recode it as a TIF file, using no compression, there will be no quality drop but the file will be bigger. Anydecenct graphics software that lets you decide what format you save in, should also let you control the compression it uses.

E.g., Paint Shop Pro offers dozens of file formats, and in most cases offers you control over the compression. In JPEG you can set the compression ratio; in TIF you can set it for non-compressed or compressed using LZW (LZW is the same algorithm as is used in ZIP files, totally lossless); and so on.

Incidentally, you can always run a little test to see if your image has been compressed or not, it's easy and safe. Just try zipping it with WinZip. If the zipped file is within 1% of the size of the original, then it couldn't be compressed any more and therefore has already been compressed. Zipping a TIF LZW file often increases the file size slightly because it adds a small header.

HTH.

andrewh
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Joined: Oct 4 1999

In order to keep things simple for yourself, you should try to define a workflow that you will use and then stick to it.

A good idea is to take the original JPEG and during all editing phases, store it as TIFF (or PSD if using photoshop). When you have completed your editing, save as 100% quality JPEG and write to CD. You can then get rid of your TIFF files to save disc space. This way you get high quality and very little loss from the original.

Andrew

rongrover
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Joined: Jun 1 2002

Hi Andrew. I do more or less as you suggested when working on a photo. However the process I have just been through was to put all my original files from the Cards onto CD and so release the cards for reuse.

I mentioned in a previous posting a few months ago that I have always kept the original card with all photo files on them. So far I have completed this for 34 cards.Mainly SM with some SD and MM. Yes I know it is alot of wasted money.

I have noticed that the CD's I used are in fact Audio CD's!!! However, they have all burnt ok and all show up when played!

All the best, Ron.