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-   -   File compresion (https://forums.steves-digicams.com/olympus-dslr-40/file-compresion-103131/)

Metalhead Oct 7, 2006 1:45 AM

I'm not sure if this goes in the newbie section or here. I have a Olympus E-500. I'm new to digital SLR's. Does the compression of the files affect the quailiy of the photo that is stored on the card?

-=edge=- Oct 7, 2006 3:38 AM

more compression means a higher loss of quality

jorgen Oct 7, 2006 4:41 AM

In order to achieve a very high compression rate, the compression program on purpose loses a little information. This means that every time you uncompress the photo, make a change, compress the photo again and save it, you lose a little quality.

In order to avoid this, some perfectionists (and many geeks :-)) store their photos as raw or as tiff (both of which results in huge files) and only creates a jpeg file for viewing.

I hasten to add that you don't lose much quality and most photographers - including me - ignore the issue. Remember that you don't need much quality to make a photo look good on the screen and that the printers are not that finegrained.


Mikefellh Oct 7, 2006 5:41 AM

The explanations so far only refer to JPG compression which is a lossy format. The higher the compression you choose (if you choose HQ (High Quality) instead of SHQ (Super High Quality)), you'll be able to fit more images on the card at the cost of lower image quality. If you want to find out more of the JPEG history and technical (that goes beyond the editing application) check out http://www.jpeg.org/

On some cameras (not Olympus, unfortunately) there's also lossless RAW compression...there is no loss during compression, and when uncompressed you get 100% of the information back. Unfortunately for us, Olympus has chosen NOT to compress RAW files (some cameras can compress a RAW file by half)...probably the reason is because it takes longer, or requires a faster processor. Some people compress their RAW files on the computer, either using a ZIP type compression, or Adobe's DNG raw format (which you WILL lose data as it's no longer Oly RAW format).

I have to admit though that I use a 4gig (Extreme III) card, and have yet to run out of space on even two outings combined on one card, shooting RAW+SHQ (almost 20 megs an image).

Metalhead Oct 7, 2006 11:43 AM

I just got it and I have it set at SQ 1/12. I guess I'mm loosing alot of detail then.


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