Confused over RAW images

cameracat (e2 Member)

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19 Oct 2010 - 11:45 AM

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The bottom line Mozzy....

An image shot in JPEG is processed for you by the camera, So apart from a very minor tweak on the computer, Its good to go straight to print or whatever.....!

An image shot in RAW will need post processing " By You " in whatever software you use, How good the result will be is dependant on your knowledge & skill in post editing....!!

The main advantage with RAW is almost total control over everything " After The Event " .....!!!

If your just shooting record shots of your little trees, Providing you do the initial shot perfectly and to your liking, Then shoot in JPEG and sRGB, Save yourself a whole lot of grief.

That said until you play around with both, You will not attain the skills/knowledge to pull the best from either.

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Kris_Dutson

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19 Oct 2010 - 11:50 AM

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RAW gives max detail and no loss of image quality straight from the camera. They can then be processed to your hearts desire in loads of different ways without damaging the original file as the RAW software works on a COPY of the original file.

Saving them to jpeg is not really the way to go as it compresses them and a myriad other things, meaning they are 'compromised' for any further use other than that for which you saved them. Pointless really, so you may as well just shoot .jpegs and be done with it.

Saving them as max size 16 bit 300 ppi .tiff files however, achieves a lot more as they can then be made smaller for web use, printed at a decent size etc., all from the same file.

And that's just for starters.

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Dean0

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19 Oct 2010 - 6:11 PM

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I think there's a lot of confusion over JPEGs and RAW image files, if I'm honest, even with myself.
I've come across professional photographers that insist that the camera should be set to take RAW images only, then I've read remarks by other pro's that have conducted comparisons between the same image in the two different formats and conclude there's virtually no difference and JPEGS should be used.

I think the confusion comes about because the technical performance advantages between the two are not fully understood by most people, even I with a degree in Electronic Engineering doesn't fully understand!
Detailed technical info is hard to come by.

In essence, what Kris is saying is right, but I'd like to fill in a few more details and explain some of the issues and give the benefit of some tests a friend of mine conducted some years ago.

RAW, JPEG.
RAW is the actual light intensity values read from the sensor chip before the camera's electronics have had chance to do any processing (other than perhaps noise reduction).

To create the JPEG image, the camera's electronics takes this RAW image and processes it, it applies algorithms to do various things, such as applying the colour balance settings, brightness, contrast, saturation.

Thus you will find, that when taking pictures in RAW mode, the images are not affected by many of the controls on the camera.

The consequence is, that a considerable amount of time is required to post-process the RAW images in Photoshop than JPEGS.

I personally, haven't really experimented with RAW yet, the reason is I get such a good result with JPEGS on my Nikon 20D.
And quite frankly, the amount of time I'll have to spend processing RAW images frightens the life out of me!
I'm not yet convinced that RAW is worth the effort..but ask me again in 6 months, my answer might be different.

The technical Issues:
Everyone talks about JPEG as being a compressed image format and as such it destroys, degrades the image.
Technically, that's only true if a lossy compression algorithm is used, which JPEG is..- most of the time!
There are lossless compression formats such as TIFFSs (if you turn the option on) which don't damage the images.

Compression algorithms fall into two types: lossy and lossless. It's important to understand the difference and recognise when each is being used.

JPEG does have a mode setting where it's lossless - and results in a larger file size - but to be safe, best to assume it's lossy, because 98% of the time it is.

So everyone goes on about how JPGs should not be used because they utilise lossy compression.
I recall years ago in the early days of JPEGs, I certainly found that to be true, with some high resolution 35mm scans being damaged by the JPEG compression, look closely enough and you could see artifacts in the image caused by the compression algorithm.

However, in all the work I've done with JPEGs in recent years, I've found this to be no longer the case.
I've quite happy printed images at bigger than A3 size with a pocket Nikon, using JPGs and with no visible signs of damage. Indeed, a friend of mine took his Canon 1D, took the JPEGS it produced and produced a near A0 - one metre print! with no signs whatsoever of pixelation effects, damage by the JPEG algorithm.

A print one metre is big enough for most people!

If you're doing repeated saving, opening, saving files, then theoretically the image will degrade as each time it's compressed some information is discarded. I say theoretically, because I've never put this to the test, and given it's easy to predict what's going to happen, I haven't bothered to conduct this test.
I'd rather open the JPEG image up once, and save as a Photoshop .psd file and only save back down to JPEG when the image is finalised and ready for sending to a printer.

Conversion from RAW to JPEG
The camera internally will do the conversion, which means applying a compression algorithm, the issue is, it's up to the camera manufacturer to control the parameters of that compression algorithm, and you as the user have no control over those parameters. They're set by the manufacturer. So one camera might do the compression better than another.
A mapping to a colourspace will also be carried out, and this is another source of errors in the conversion process.

So the question as to which gives the best result really depends on your camera. In theory RAW gives the best result, but at what price? Considerable time processing each image inside Photoshop applying colour cuves, levels, brightness, contrast.

It's believed that RAW has a greater dynamic range, that there's more detail captured, but I don't really have any evidence to support this, and from what I can see of people's remarks on the internet, neither do they, just a belief that RAW is better in those areas. Having said that, I've examined the histogrrams for a RAW image and it's JPEG equivalent and found them to be very differfent. It seemed to me - and it would require further investigation to establish conclusively - that the RAW image had greater dynamic range.

So how do I use RAW?
I don't yet. I have found JPEGS from the 20D to be superb and am able to print quite large prints at high quality.
How do I plan on using RAW? I'd set the camera to take a RAW image and a large format JPEG image simultaneously.
Then I have the RAW image too, so for the top notch photographs, I can use the RAW and experiment with that to ensure the very best result.

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