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Difference between raw and Jpeg

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Offline RaduP

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Difference between raw and Jpeg
« on: 16 / May / 2008, 15:08:18 »
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I was wondering, what are the exact differences between raw and Jpeg?
So far I've noticed the following:
1. WB
2. Noise reduction
3. Sharpening(?) or is that the result of noise reduction?
4. Minor compression artefacts
5. Reduced color range (8b rather than 10b)

Is there anything else?
And is there a sharpening step taken by the camera before saving the Jpeg file? Can this step be removed?

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Offline whim

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Re: Difference between raw and Jpeg
« Reply #1 on: 16 / May / 2008, 15:23:47 »
Also: the raw image is larger: before converting to jpeg the edges are removed.
Example: for A620 (7 Mp), raw = 3152x2340, jpeg (max) = 3072x2304.

wim

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Offline BB

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Re: Difference between raw and Jpeg
« Reply #2 on: 16 / May / 2008, 15:54:02 »
Yes, sharpening is a separate function... In a photo editor, you might see this called an "unsharp mask"...

Nice article on why it is called unsharp mask (from film days) and some examples of what its effects are:

Unsharp masking - Wikipedia, the free encyclopedia

Basically, RAW is the complete RAW data (in original rgb pixel sensor data) that has been transformed into a RGB type data file and RGB mapped for each pixel. And lots of other data "tossed", transformed (including white balance/sensor corrections), and compressed into  the "final" digital image.

If you want to do your own work, starting with RAW (or a JPEG w/little compression, with no saturation/sharpening performed), allows you to make the photo you want without you accidentally making artifacts look worse when you do your changes.

-Bill

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Offline RaduP

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Re: Difference between raw and Jpeg
« Reply #3 on: 16 / May / 2008, 16:01:22 »
Yes, I know what raw is and what the sharpening is, I was just wondering what kind of processing the camera does for the raw file.
Whim, thanks for the info about the file size, didn't know that the jpeg removed the borderers.

So, is it possible to remove the camera sharpening? If I want to do any, I'd rather do it myself..


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Offline whim

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Re: Difference between raw and Jpeg
« Reply #4 on: 16 / May / 2008, 16:05:55 »
Not in any of my 3 Canons (can't even adjust it, unlike some other cheap cams)
So I guess the only way is to shoot raw, that way YOU determine what post-processing
gets done. The disadvantage is, that you also have to make all other post-processing
settings/decisions ...

wim
« Last Edit: 16 / May / 2008, 16:07:45 by whim »

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Offline RaduP

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Re: Difference between raw and Jpeg
« Reply #5 on: 16 / May / 2008, 16:11:22 »
Yes, I was afraid this would be the answer :/
The jpegs are so convenient, but the raw contains the good data :)
My Rebel 300D does a great job with the jpeg, most of the time there is no need for raw.

 

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