png for storing pictures?

[stefG5]

i want to make a master back up of my whole picture collection onto dvd's. i do not want to use .jpg format since it is a lossy format and the master copies should not be accidently altered in any way.

so, in my quest for a decent format im now torn between png and tiff. im surprised at the filesize of tif's: about 18MB per file for a max quality jpg coming out of my G5.

i find the filesize of a png is about 1.6 times smaller than a tiff. is there a disadvantage in storing pictures in png?

would i loose quality by saving from raw/jpg to png to tiff and back a few times?

take it easy
stefan

[Jesper]

would i loose quality by saving from raw/jpg to png to tiff and back a few times?

No, PNG uses a lossless compression algorithm (similar to ZIP compression). That means it doesn't affect the image quality. PNG is a very nice, interesting open standard file format, but unfortunately it never became very popular, because JPEG and TIFF were already widely in use when PNG was invented.

The TIFF format also supports lossless, ZIP-like compression - have a look in the conversion program that you're going to use if you can specify that you want your TIFF files to be compressed.

[Scottes]

PNG is very slow to compress and notvery quick to decompress. A few tests that I did showed me that it's not worth my time to use PNG. Blank CDs & DVDs are cheap, and I don't have enough patience to wait for a PNG to open, let alone compress.


This might not matter to you, but TIFFs can save layers, whereas PNG can't.

[stefG5]

thanks for these speedy replies. im using Fireworks to batch all my files from jpg to tiff (PS requires me to create such a batch action, too complex). FW offers tiff24 or 32 and there is a difference in filesize.

whats the difference between 24 and 32 and what should be used for photography?

[Scottes]

I *believe* that the 32-bit version of TIFF allows for storage of an alpha channel, which could be useful if you store masks. Otherwise it's not much use to most people.

[stefG5]

superb, thanks v much!

[snibbetsj]

I believe that the LZW compression of TIFF files is also lossless. I use this and the files sizes are much smaller. It all depends on the content.

Jeff

[Scottes]

I believe that the LZW compression of TIFF files is also lossless. I use this and the files sizes are much smaller. It all depends on the content.

Yes, LZW is lossless. But it's a relatively poor compression algorithm for photos, but it's great for logos and other stuff with a low number of colors. Given a noisy image LZW might actually make the image 1.5 times the original size! I stopped using LZW because I found myself saving space only 2/3 of the time, and the other 1/3 got bigger.

TIFF with ZIP compression is the way to go, but many many programs don't support TIFF compression.


Does anyone happen to know if PSD automatically compresses or not? I save PSD only when I use layers which isn't often. I don't ever recall seeing a compression option when saving.

[snibbetsj]

Yes, LZW is lossless. But it's a relatively poor compression algorithm for photos, but it's great for logos and other stuff with a low number of colors. Given a noisy image LZW might actually make the image 1.5 times the original size! I stopped using LZW because I found myself saving space only 2/3 of the time, and the other 1/3 got bigger.

TIFF with ZIP compression is the way to go, but many many programs don't support TIFF compression.

Hmm, I didn't know that. I'll start using ZIP and see how that works for me. Thanks for the info :)

Jeff

[PacAce]

Are your original images RAW or are they shot in JPEG? Just curious because if they're already shot in JPEG, converting them to another format like TIFF or PNG is not going to gain you anything. AAMOF, you'll end up with a bigger file than you originally started out with.

If the originals were shot in RAW, then forget I asked. :)

[stefG5]

most of my originals are in jpg. im not too concerned about the file size. im rather looking for a format that is good to work with, without having to worry about losing quality when making saves ...

[Scottes]

...without having to worry about losing quality when making saves ...

A few of us did a test with re-saving JPGs over and over. You don't lose that much unless you save a couple dozen times. And it will be even less noticable if you work in 16-bit mode.

But if you're not worried about space then go TIFF. It's very nice to work with and fast to open and save compared to any other format.