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What is RAW

 
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Gary W Brown



Joined: 02 Mar 2008
Posts: 129
Location: Omaha, NE USA

PostPosted: Sat Mar 15, 2008 11:21 am    Post subject: What is RAW Reply with quote

Greetings all, I've been sitting quietly in the back of the class just soaking up the most amazing amout of material...Now I have a question. What is RAW? (answer in somewhat elementary terms, please). A follow-up question is how does it relate to or differ from jpg? Gary
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puzzledpaul



Joined: 06 Aug 2006
Posts: 414
Location: UK

PostPosted: Sat Mar 15, 2008 12:32 pm    Post subject: Reply with quote

Hi - does this help?

http://www.luminous-landscape.com/tutorials/understanding-series/u-raw-files.shtml

pp
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Gary W Brown



Joined: 02 Mar 2008
Posts: 129
Location: Omaha, NE USA

PostPosted: Sat Mar 15, 2008 1:20 pm    Post subject: Reply with quote

Thanks puzzledpaul, It was just what I needed, like spending an afternoon at the "penny university". Gary
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DaveW



Joined: 04 Aug 2006
Posts: 1702
Location: Nottingham, UK

PostPosted: Sat Mar 15, 2008 2:15 pm    Post subject: Reply with quote

RAW for once is not an acronym, as are most things computer or camera related, it simply means raw data taken straight from the cameras sensor and hardly processed in camera therefore not yet an image as JPEG's are, but needing converting in a RAW converter to produce the image and further manipulating in photo editing software.

As your computers processor and memory is far more powerful than the cameras the raw data can be processed far better using far more complex algorithms thus giving you far more control over the final result that can then be converted to JPEG's afterwards if required.

When the camera itself processes a JPEG it discards a lot of the data produced by the sensor, which is why camera produced JPEG's take up less room on the memory card than do RAW ones. RAW retains all this data which is transferred to your image processing program, thus giving you more manipulation options in post processing.

The image you see on your camera monitor screen when solely taking RAW, or as a thumbnail in processing software before conversion, is not the actual RAW image which has not yet been processed, but an embedded JPEG just to illustrate what you have taken. Only after the data has gone through a RAW converter program does the raw data become an actual image.

DaveW
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Gary W Brown



Joined: 02 Mar 2008
Posts: 129
Location: Omaha, NE USA

PostPosted: Sat Mar 15, 2008 7:10 pm    Post subject: raw and another question Reply with quote

Thanks Dave, it's great to get replies from all around the world. I'm putting pins in my map and I really appreciate all answers. Here is another related question. What is the physical difference between the sensor that is 1.4mp or so, and a sensor that is 5, 6, or even 7mp. I'm having a personal pool. I think I will get 6 responses with in the hour. Gary
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 19975
Location: Richland, Washington State, USA

PostPosted: Sat Mar 15, 2008 9:38 pm    Post subject: Reply with quote

Gary, it seems you lost that bet with yourself. But that's no surprise -- most of our members are eastern US and European, so your posting happened to be night or very early morning for them.

The apparently tongue-in-cheek answer to your question is that the 1.4 mp sensor is carved up into fewer little squares.

I say "apparently tongue-in-cheek" because that answer is in fact very serious.

For example, in my current menagerie I have the following cameras:
  • Canon 300D, 6.3 megapixels, 3072x2048 in 22.7x15.1 mm, 7.4 microns/pixel.
  • StarShoot Solar System Color Imager II, 1.3 megapixels, 1280x1024 in 6.4x4.8 mm, 4.7 microns/pixel.
  • Canon A710IS, 7.1 megapixels, 3072x2304 in 5.76x4.29 mm, 1.9 microns/pixel.
It should be clear from the numbers that there is no obvious pattern here. The 300D (a DSLR) has by far the largest sensor and also the largest pixels, but not the most pixels. The A710IS (a compact zoom) has both the smallest sensor and the most pixels, giving by far the smallest pixels. The StarShoot (a digital eyepiece for telescopes) has by far the fewest pixels, but not the smallest sensor, and a pixel size that is smack in the middle.

If you are hoping for some clear and consistent relationship between pixel count and other parameters like noise and sensitivity, you are going to be disappointed. Given the same fabrication technology, smaller pixels saturate with fewer photons and therefore have higher noise levels. But fabrication technologies vary, as do the associated electronics and optics, so it's really impossible to predict from advertising specs how well a particular sensor or camera will perform.

Why are you asking the question?

--Rik
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Mike B in OKlahoma



Joined: 04 Aug 2006
Posts: 1048
Location: Oklahoma City

PostPosted: Sat Mar 15, 2008 10:29 pm    Post subject: Re: raw and another question Reply with quote

Gary W Brown wrote:
What is the physical difference between the sensor that is 1.4mp or so, and a sensor that is 5, 6, or even 7mp. I'm having a personal pool. I think I will get 6 responses with in the hour. Gary


One thing you may be thinking of....The sensors in DSLRs are much larger than the ones in most "pocket" or consumer digicams with fixed lenses (a just-announced one from Sigma is an exception). Barring major differences in some other factor, the small sensors will have many more of the problems with noise and saturation that Rik mentioned.

Some DSLRs have different sized sensor. This makes some difference, but not as much, and is more prone to being distorted by the other factors Rik mentioned, especially newness of the sensor!
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augusthouse



Joined: 16 Sep 2006
Posts: 1195
Location: New South Wales Australia

PostPosted: Sun Mar 16, 2008 1:34 am    Post subject: Reply with quote

When you shoot in RAW and use a preset custom white balance - where does the custom white-balance data go and how is is retrieved?

The answer should be obvious, but it eludes me at the moment.

Craig
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DaveW



Joined: 04 Aug 2006
Posts: 1702
Location: Nottingham, UK

PostPosted: Sun Mar 16, 2008 4:45 am    Post subject: Reply with quote

I think the advantage of RAW Craig is it just transfers what the sensor "sees" as data. Things like white ballance are alterations to this basic sensor data done by the camera's processing of the image after taking it and not before, unlike putting a filter on a lens which affects the taken image before it is recorded on film (or as it would with digital with a correction filter on the lens).

Therefore in shooting RAW you simply transfer this virtually unmodified data to your computer and so can adjust the white balance in the RAW Converter in post processing rather than the camera doing it before transferring it to the memory card.

The advantage of RAW is all adjustments to the image can be done in arrears on computer rather than having to be set on the camera beforehand and then you being stuck with the result. With RAW, providing you do not modify the original RAW data and keep it like your "negative" using only a copy of it to work on, you can continue to manipulate different versions of the shot as you want with different white balance settings, exposure, saturation etc etc, which you cannot do to the same extent with an already camera processed JPEG.

Somebody will no doubt correct me if I am wrong?

Gary see:-

http://www.surething.com/ST/Category.asp?CatCode=FEB04_MEGAPIX

http://luxars.com/index.php?http%3A//luxars.com/matrix/articles/sensorsizes/index.html

DaveW
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puzzledpaul



Joined: 06 Aug 2006
Posts: 414
Location: UK

PostPosted: Sun Mar 16, 2008 5:02 am    Post subject: Reply with quote

This guy is one of many who swear 'by' rather than 'at' using RAW because of the processing options available.

(Worth having a quick shufties at his pics too, btw)

pp

http://www.flickr.com/groups/mega_shots/discuss/72157602404722008/
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 19975
Location: Richland, Washington State, USA

PostPosted: Sun Mar 16, 2008 9:16 am    Post subject: Reply with quote

augusthouse wrote:
When you shoot in RAW and use a preset custom white balance - where does the custom white-balance data go and how is is retrieved?

All information related to the image gets packed into the same file, with a bunch of tags and wrappers to keep it straight. It's basically the same technique that lets JPEG and TIFF files also contain information about the camera type, lens focal length, exposure time, etc. etc.

If you're extremely curious, download the source for dcraw and browse through it.

--Rik
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Gary W Brown



Joined: 02 Mar 2008
Posts: 129
Location: Omaha, NE USA

PostPosted: Sun Mar 16, 2008 9:39 am    Post subject: Reply with quote

Good morning everyone. Rik, not knowing the demographic constitution of the group, I made an uninformed yet optimistic wager with myself. I am a winner none-the-less...there were 5 responses when I joined in this morning and the links and advice were exactly what I was hoping for. Thanks to all of you. Gary. PS I'm putting a pin in my map every time I get a reply from a new location...just like when I was a kid. BTW, if your location is listed as a general area like "USA" and you feel uncomfortable listing your address, could you please include your Lat. and Lon. coordinates? (there woould be a smiley pic here, if I knew how)
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rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 19975
Location: Richland, Washington State, USA

PostPosted: Sun Mar 16, 2008 10:09 am    Post subject: Reply with quote

Gary W Brown wrote:
(there would be a smiley pic here, if I knew how)

Just click on one of the "Emoticons" that you should see to the left of the text window where you're typing your message. That will inject a text smiley like : D (but without the space). When you preview or submit, the text : D will be rendered by the forum software as Very Happy (the graphic smiley). If you like, you can just type the : D (no space) by yourself -- it makes no difference to the software. Sometimes this happens by accident, such as when 8 ) (no space) turns into Cool. Piece of cake, once you get used to it. Laughing

If the 20 basic emoticons aren't enough, click on "View more emoticons" to be offered another couple hundred.

--Rik
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Gary W Brown



Joined: 02 Mar 2008
Posts: 129
Location: Omaha, NE USA

PostPosted: Sun Mar 16, 2008 11:38 am    Post subject: Reply with quote

Shocked Never guessed it could be so simple Embarassed Nothing like a little practice to cement the concept Very Happy Thanks, Gary
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