Quality photos

[poogotflung]

Ive been using photoshop cs with my olympus e-500 and ive been having a problem when i save the photo it seems to have killed pixels. i have been taking my pictures in jpg hq. i would also like to know the major differences between jpg and RAW.

[Medley]

The main difference is editability. jpg has 8 bits per channel, or 256 possible tonal variations in each of the Red Green and Blue channels. RAW has 12 bits/channel (which, for reasons unknown to me, is put in a 16 bit format), or 4096 tonal variations.
So you're starting with 16X more information in a RAW capture.
However, the human eye really can't tell the difference between 8 bits and 16, and the debate rages on as to wether or not there's a noticable difference in print. So what good is all that extra information?
Levels, curves, Shadow/highlight, and several other commands in Photoshop all discard information every time you apply them.So while the eye can't tell the difference between 4096 tones and 256 tones, it can see a difference in 1024 tones and, say, 40.

Now consider your workflow. When you open a Raw image, Photoshop opens the Adobe Camera Raw (ACR) plug-in. Get to know the features of this gem. It lets you do several of the same edits you can do in Photoshop, but there is no loss of information. When you're done in ACR open the image as a 16 bit psd. Now that you're in Photoshop proper, the lossy edits apply. But you still have that 12 bit cushion. Some of the filters and a few of the tools aren't available in 16 bit mode, but most of the important ones are.
Convert to 8-bit to use any tools that weren't available in 16 bit. You'll also need to convert to 8 bit to save the file as a jpg.

If you do a lot of Photoshopping, I recommend shooting in RAW. Once you get the hang of the workflow, I think you'll find that your images look better overall.

Oh, and to keep from losing information when you save, save the file as a psd. It takes up more memory, but the image will be exdactly the same when you open it as it was when you saved it.

-Joe U.

[Canuck935]

Also every time you save a .jpg it gets recompressed, so even if you do nothing else but open it and resave it you will lose information..

[Rocket_Scientist]

...RAW has 12 bits/channel (which, for reasons unknown to me, is put in a 16 bit format)...

I'm sure the reason would be that virtually all computers (at least personal computers) are byte-addressable (8-bit) machines, and it is simply convenient, or more efficient, or easier, however you wish to characterize it, to use multiples of 8 bits.
[Of course, this could lead to a lengthy discusssion... since all machines, by definition, are byte-addressable. It's just that with the proliferation of PCs, and smaller, embedded processors, we have come to "define" a byte as 8-bits.]

[Ronnoco]

In Photoshop, if you lose pixel information it is usually due to your editing of a jpeg image.
As indicated the routine is to shoot in RAW and conviert to 16 bit: psd, tiff, or jpg.(16). Do as much editing as you can in 16 bit, convert to 8 bit and carefully finish your editing. Save sharpness and noise reduction work until the very end. Refer to the histogram to ensure that you are not losing pixel info. due to usually too heavy an adjustment on the editing controls.

Ronnoco