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07-26-2009, 06:00 PM   #1
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RAW files

HI guys

i hope you can help me with some confusion over RAW files.

I have only shot JPEG up until now but have been doing some reading on the RAW processing etc.

I am trying to get my head around if i should use RAW and how to use / process those files.

If i am reading correctly RAW has the raw data from the sensor with no processing applied by the camera......if thats the case does that mean (and i m sure the answer will be no - but why?) that you can set the ISO to 100 (so there is less noise) for all shots and have the shutter speed / aperture to a level that the camera doesnt like (flashing lights) but fix this in post processing???

hope somone can shine a light on this subject for me


Adrian

07-26-2009, 06:21 PM   #2
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The short answer is the RAW is the equivalent of a film negative in the digital world. It has much more information stored within than a JPEG. This allows, even with perfectly exposed pictures, the photographer much more room to play or adjust even the most minute of things within the picture. Here is a great article from the article section that will have much more details than any short blurb I could write:

https://www.pentaxforums.com/forums/post-processing-articles/40647-some-expla...-benifits.html
07-26-2009, 06:40 PM   #3
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As mentioned, a RAW file is in some ways a lot like a film negative. If your exposure is slightly over or under exposed, or the contrast is a little off from what you like, you can make adjustments in RAW just like you could in a darkroom. However, just like with a film negative, if you shoot something that is horribly over/under exposed beyond repair, your final product will look like crap no matter what (unless for artistic reasons you want a technically poor photograph of course).
07-27-2009, 08:47 AM   #4
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QuoteOriginally posted by milesy Quote
If i am reading correctly RAW has the raw data from the sensor with no processing applied by the camera......if thats the case does that mean (and i m sure the answer will be no - but why?) that you can set the ISO to 100 (so there is less noise) for all shots and have the shutter speed / aperture to a level that the camera doesnt like (flashing lights) but fix this in post processing???
No. ISO, shutter speed, and aperture are not "processing" done by the camera after the image has been taken, but things that control how the picture was taken in the first place. RAW only lets you control things that the camera processes *after* the shot - things like white balance, sharpness, contrast, saturation, etc.

07-27-2009, 11:33 AM   #5
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ISO

All digital slrs have what is called a "Base ISO". For most, if not all, Pentax dslrs, this is 100. When you set the ISO higher than that, the camera electrically amplifies the signals from each pixel, at the time of exposure.

Its a little bit like cranking up the volume on a stereo. At high volumes, distortion creeps in. All electronic components exhibit "noise", which to an electrical engineer means random electrical signals that are not part of the data being recorded or transmitted, but are created spontaneously within the component itself. When you turn up the gain, or volume, you amplify not only the desired signal (the image), but the electrical noise.

Therefore, what is recorded in the .PEF or .DNG file is the amplified signal from the sensor.

However, because raw images contain all the data from the sensor, unlike jpegs, in which some data is discarded, I have found that I can deliberately underexpose a shot in raw, by as much as two stops. In post-processing, those two stops can be recovered, without losing shadow detail. I find this useful in very low light, when even SR won't stop camera motion. When you're down around 1/4 second, SR may help, but it won't stop all motion. If I deliberately shoot at 1/16 SR has a much better chance of saving the image.

On the other hand, some camera settings, such as white balance, ARE applied after the shot. When shooting in raw, the WB setting is stored as part of the .PEF or .DNG file, but it is not applied to the image. When the image is displayed, either in the camera, or on the computer, the WB setting is applied to the displayed image. If you wish to change it, the raw image is re-interpreted and the new WB setting is applied.
07-28-2009, 07:16 AM   #6
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First off, your camera ONLY shoots RAW. When you select JPG, the camera takes the RAW data and pipes it into it's on-board JPG processor to generate the JPG "image" to save to the card.

When you shoot RAW, the RAW "data" goes directly to the card and is not an image.

To generate an image, you use a RAW processor (software on your PC) which turns the data into a viewable image, much like the camera's JPG processor. The difference is that YOU have complete control over the image generation process. You can change the white balance, adjust the contrast/brightness/black point/etc....

So you can leave these decisions up to the camera's little processor (and hope it makes the right decisions since they are irreversible), or save the decisions for later where YOU have complete control over it.
07-28-2009, 07:19 AM   #7
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You even have the choice of the RAW Processor, and they have an huge impact on the final image quality!
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