Originally posted by justinr Now as far as jpegs are concerned I'm still not happy about the answers I've received in that if they are more 'efficient' then why not set them at 5mb and then boast of how jpegs from your camera can be blown up even larger? Accuse me of short sighted cynicism if you like but I imagine that there is some sort of marketing ploy at work here. If you are a camera manufacturer and have 10 million pixels to play with why not make the most of them, unless it discourages people from upgrading of course.
Oy, that's not cynicism, that's paranoia. By the way, TIFF files can be compressed too. They can be compressed losslessly and with loss. I can use JPG compression, LZW compression, ZIP compression and a bunch of other compression methods in TIFF files, or I can leave them uncompressed.
Here's the REAL difference between lossless and lossy compression:
Lossless
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You take a file, you compress it. It takes up less space on your hard drive because all duplicate data has been combined together, along with information on which address space this duplicate data needs to show up at. When you uncompress it, you end up with the exact same original file, bit for bit, without any difference whatsoever (this is what's used for RAW compression)
Lossy
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You take a file, you compress it. It takes up less space on your hard drive because of the same reasons above AND some of the data was deleted. When you uncompress it, you end up with a file that is different from the original. Bits are missing, others have been moved around. For music and pictures, this isn't necessarily such a big deal depending on the algorithm used (this is what's used for JPG, MP3, most WMA and WMV, MPG, DIVX, etc)
Now as far as pictures are concerned, I think a bit of pixel-peeping is in order. So here's a picture I took with my K-7 using a Super Takumar 50mm F1.4. Shutter speed was 1/25 @ ISO400 and I think the aperture was F4.5 or so.
I developed these from RAW, then used Gimp to create a bunch of files with different compression levels. Here's a nearly-pristine version saved with all the maximum JPG settings and compression at 100/100 (Gimp has tons more JPG compression options than Photoshop):
So here are some 100% crops of different compression versions. Keep in mind, I kept re-saving the entire, unedited original uncompressed file into a JPG at varying compression levels.
Here's one from the uncompressed version (straight from RAW, there was no re-saving it)
This file is a 34.3mb TIF file. It is uncompressed.
And here's another one after I saved the image at maximum JPG settings:
I'd say the difference is imperceptible. Detail lines like this are where JPG compression tend to show the most. This file was 10.9mb.
This one was saved at 95/100 compression level, the rest left at best quality:
Again, no perceptible difference. This file was 3.8mb. That's a huge difference! And yet there's absolutely no perceptible difference in quality. Also remember that this is a 14 megapixel image, and it's already about the same size as your 10 megapixel images.
This one was saved at 80/100 compression level, the rest still at best quality:
Wow, I can
maybe start to make out some compression artifacts around the contrast lines. Keep in mind of course that this is a 100% crop, which wouldn't actually be noticeable in a normal-sized print. File size for this one was 1.3mb!!!
This second-last one was saved at 40/100 compression level, and still everything else at maximum:
Now the compression artifacts are more obvious. The JPG squares are becoming more visible. Still when viewed in full size, you'd be hard pressed to tell they're there. File size was 465kb (wow, for a 14 megapixel image?!?)
This last one was also saved at 40/100 compression level, but the subsampling was set to its worst quality:
That is one fugly picture. The JPG squares are clearly visible. Everything looks bad. And not surprisingly, the file size for this one was 342kb.
What does this mean in the grand scheme of things? By all means, please tell me which one of these was saved at 100/100 (455kb) and which one at 95/100 (155kb)?
(no fair looking at filenames)
Just to complete the trifecta, here it is at 40/100 and low quality settings (25kb):
ewwwwwwwwww, that's fugly!
Oh, and this one's for Damn Brit. Here's what your camera's AdobeRGB JPG files look like when they come straight from the camera and into a web browser:
The colours are all wrong. They're all slightly darker and grayer than the original. This isn't the best example since red is fairly well matched in both colour spaces, but the difference is still pretty evident. It's much worse with greens and blues.