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PostPosted: Mon Feb 15, 2010 9:58 pm 
I've searched around the forum but I'm unable to find anything about what the camera does before making the final jpeg.

For instance, using RAW+JPEG produces a RAW image that's 19.8"x13.2" while the JPEG is 66"x44". When converting from RAW to JPEG via CS4, the JPEG created is 19.8"x13.2". In addition, the resolution is lower for the incamera JPEG (72 vs 280).

Is there a standard guideline the camera goes through when creating JPEG images? The JPEGs produced are great and I would like to replicate except when I want a different white balance or tweak minor things.

Thank you


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PostPosted: Mon Feb 15, 2010 11:47 pm 
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If I understand your question right here is what I think may be the answer...

When shooting in RAW the camera saves all info produced as a RAW file allowing you to make adjustments later to things like WB and other things.

When you shoot in jpeg the camera automatically makes these adjustments for you and compresses the file thus not taking up as much disc space allowing you to A) store more media on a disc and B) allow for faster and longer continuous shooting. The images saved in jpeg dont let you make the adjustments after-the-fact that RAW files do.

As far as I know each manufacturer uses a different format for their RAW files and also in converting them to jpeg in camera.

The final question pertaining to this is if shooting in RAW is even nessessary creates a huge debate and is one which has been discussed before both here and on other forums. At the end of the day this final question is one you will need to answer for yourself after studying the topic more.

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PostPosted: Tue Feb 16, 2010 2:53 am 
Welcome to the forum yohoe.

I'm not sure why you are getting images of different sizes and resolutions. Every camera would have a different set of tweaks that they apply to JPEGs and I notice that this is almost always saturation, sharpening, noise reduction and a more contrasty tone curve. If you compare the shots in your RAW+JPEGs, the difference is easy to spot.

I don't know what camera you use or what software came with it but some will allow you to apply a preset to your RAW files that will allow you to match the JPEG output from the camera.


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PostPosted: Tue Feb 16, 2010 9:33 am 
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You might want to read these web pages about JPEG some of them get quite technical but in a DSLR what actually happens will be down to the camera manufacturer mixing their image processing algorithms (some determined by the camera settings) with those of the JPEG standard to create a final image.

http://en.wikipedia.org/wiki/JPEG
http://www.faqs.org/faqs/jpeg-faq/part1/
http://www.webdevelopersnotes.com/graph ... rithm.php3

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PostPosted: Wed Feb 17, 2010 3:13 am 
Thank you everyone for the replies. I'm shooting a Canon T1i and I guess I don't have an eye for the alternations yet but I'm sure it will become more prevalent with time. I'd have to fool around with the photos to see what they did to match.

I would like to print the photos around 20"x30" and I'm afraid to increase their size from raw as it might destroy it, which is why I would favor the JPEG.


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PostPosted: Wed Feb 17, 2010 3:25 am 
One way to see what is going on is to shoot in RAW+JPEG. That way you can do a side by side comparison. Things that a camera will typically do when generating the JPEG include:

Noise reduction
Sharpening
Contrast/saturation/etc adjustments
Processing to remove chromatic aberration
The T1i does correction of vignetting caused by the lens
etc.

In other words, most of the things that Lightroom makes available to you when working with RAW files. The difference is that a piece of silicon in a camera is fundamentally limited in the choices it can make when processing a particular photo. With practice, a human can become much better at deciding what processing a particular photo needs, hopefully resulting in bitter pictures.


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