Topic: Tiff compression?? (Read 15956 times)

CynthiaM · « **on:** February 07, 2009, 03:12:33 pm »

Have recently come across several posts in numerous forums regarding the merits of saving processed Photoshop files (with multiple layers) as tiff files. My question regards what type, if any, compression should be used and should it be applied to the image (LZW vs ZIP) and/or to the layers (RLE vs ZIP). In other words, when you get to the tiff dialog box, for Image compression you have to choose between None, LZW or ZIP with none selected as the default, and under Layer Compression you have to choose between RLE or ZIP. Of note, a file saved without image compression but with RLE layer compression ended up at 630mg, but if saved with zip layer compression it came out to 398.47mg. Not much difference if saved with ZIP image and ZIP layer compression; 391.38.
So I am a little confused as to how this dialog box should be set up.

Thanks for the advice.

Roger Calixto · « **Reply #1 on:** February 07, 2009, 03:34:16 pm »

According to the unofficial tiff website LZW is the choice for quality over compression ratio, or deflated without any compression (wasted space anyone?). The table they provide there is pretty complete, if you understand geekese. If not, bottom line is LZW is lossless and a good overview can be seen here

Panopeeper · « **Reply #2 on:** February 07, 2009, 03:43:35 pm »

Quote from: kingtutt

According to the unofficial tiff website LZW is the choice for quality over compression ratio, or deflated without any compression (wasted space anyone

You misunderstood that table. Both LZW and ZIP are lossless, there is no such thing as "better quality". The "quality" referred to in that table relates to the color space and bit depth.

My experience is, that LZW is better (results in smaller file) with 8bit and ZIP is slightly better with 16bit.

bill t. · « **Reply #3 on:** February 07, 2009, 07:57:00 pm »

What I have wondered about routinely using LZW compression is...supposing you save a file at a contrast where sequential pixels are so close together numerically that they are "compressed" or treated as having the same value. I suppose that would be fine if no more processing were to be done on the image, but wouldn't the results of a subsequent contrast expansion then be inferior for an LZW compressed file versus a completely uncompressed file? And is LZW run-length encoded, or something else?

Panopeeper · « **Reply #4 on:** February 07, 2009, 08:19:43 pm »

Quote from: bill t.

you save a file at a contrast where sequential pixels are so close together numerically that they are "compressed" or treated as having the same value. I suppose that would be fine if no more processing were to be done on the image, but wouldn't the results of a subsequent contrast expansion then be inferior for an LZW compressed file versus a completely uncompressed file?

Bill, both LZW and ZIP are lossless compression methods. This means, that the original data will be reconstructed down to the last bit.

What you are alluding to is the lossy compression of some raw data, like Nikons (optional with the new cameras).

See this thread

NikosR · « **Reply #5 on:** February 08, 2009, 03:53:18 am »

Quote from: bill t.

And is LZW run-length encoded, or something else?

It's not an RLE algorithm, but even if it were it would still be lossless.

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

I think that nowdays with the multitude of lossy compression algorithms being employed in imaging (still and video) and sound / music, people have forgotten that there IS such a thing as a lossless compression algorithm. These things existed long before any lossy compression algorithms were employed for individual applications.Many such algorithms have been invented to cater for different applications: http://en.wikipedia.org/wiki/Category:Loss...sion_algorithms

rcannonp · « **Reply #6 on:** February 08, 2009, 08:43:49 am »

I've found that Expression Media has trouble with importing TIFFs saved with zip compression. Zip layer compression didn't seem to be a problem though.

CynthiaM · « **Reply #7 on:** February 08, 2009, 09:01:52 am »

[quote name='CynthiaM' date='Feb 7 2009, 03:12 PM' post='258210']
Of note, a file saved without image compression but with RLE layer compression ended up at 630mg, but if saved with zip layer compression it came out to 398.47mg. Not much difference if saved with ZIP image and ZIP layer compression; 391.38.
So I am a little confused as to how this dialog box should be set up.

Quote

What I specified above is typical of the file size I save from Photoshop and these are 16 bit files.

Are you all setting up BOTH image compression and layer compression and if so, which compression is suggested for each?

CynthiaM · « **Reply #8 on:** February 08, 2009, 09:10:41 am »

Quote from: CynthiaM

Of note, a file saved without image compression but with RLE layer compression ended up at 630mg, but if saved with zip layer compression it came out to 398.47mg. Not much difference if saved with ZIP image and ZIP layer compression; 391.38.
So I am a little confused as to how this dialog box should be set up.

(Whoops! Sorry, same as above but I figured out how to "quote.")

What I specified above is typical of the file size I save from Photoshop and these are 16 bit files.

Are you all setting up BOTH image compression and layer compression and if so, which compression is suggested for each?

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