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View Full Version : RAW what is it, and what does it let you do



Old-Man
05-06-2007, 12:28 PM
I see a lot of you talk about RAW, what is it and what does it let you do? Sorry I'm sure this is a dumb question to some of you, but I'm just starting out with this camera stuff. :rolleyes:

AlexMonro
05-06-2007, 01:34 PM
Raw is the raw image data from the camera sensor, without (usually) any processing by the camera, or the compression that the JPEG format introduces. Sometimes known as a digital negative, it allows you more control at the post processing stage to allow you to optimise things like colour balance, sharpening and contrast.

JPEG was originally designed as a format to transmit photos on the internet, and a high priority was given to compression, in order to reduce file sizes and transmission times. Unfortunately, one effect of the form of compression used is that it partly works by throwing away some of the fine detail in the picture. Normally, the level of detail lost isn't very noticeable when viewing a picture onsceen, but if you need to manipulate the image, you can soon start seeing the compression artefacts. JPEG is also limited to 8-bit colour depth, allowing only 256 possible levels or red, green and blue for each pixel, whereas most mid to high end cameras actually record 10, 12 or 14 bit colour depth on the sensor, allwoing 16384 different levels of each primary colour, and all this data is included in the RAW file.

Most RAW file formats include details of all the camera's settings, which allows the RAW processing program to automatically produce converted images, usually in TIFF or JPEG format, that are identical to what could have been produced by the camera. However, they give you the additional flexibility that, if you find some of the settings weren't quite right, you can change them in the conversion program, rather than having to go back and re-shoot the scene. You can sometimes even rescue incorrect exposure by up to a couple of stops.

TIFF files can also avoid compression losses, and allow up to 16 bit colour depth, but they are usually created with all the camera processing, which is sometimes difficult to change if it's not quite right.

Norm in Fujino
05-06-2007, 08:51 PM
My personal preference as an explanation for raw is "digital latent positive," in other words, the raw file is like slide film immediately after exposure, before any developing has been done. The greatest thing about the raw format is that one can save the original raw file and go back years later, with new raw developers and develop that latent image again, as many times as one wants, without changing the original latent image on the "film." Aside from that, as Alex points out, raw includes more data, without compression losses, so (as one example) you can develop the image for greatest resolution when doing large prints.

toriaj
05-08-2007, 07:30 PM
In simpler terms ... using RAW requires more post-processing, but it allows you to have better final results than JPG would have.

coldrain
05-12-2007, 11:48 AM
(Almost?) all DSLRs have sensors that record 12 bits of light per photo diode.
The sensors only can look at the intersity of light, they are colour blind.
To actually make colour photos, they put filters in front of the diodes (the pixels).
It looks something like this:

GRGBGRGB
BGRGBGRG
GRGBGRGB
BGRGBGRG
GRGBGRGB
BGRGBGRG

As you can see, a picture like this would not look very attractive, with just values of green red and blue. So what they do is to guess, or "interpolate" the level of blue and from neighbouring red and blue pixels with green pixels, green and red with blue pixels, and blue and green with red pixels.
The only camera that actually captures red, blue and green per pixel is the Sigma SD14 (this results in a LOT sharper photos).

RAW saves (or is supposed to save) what the sensor sees, so it saves the green, the red and the blue pixels.
In the RAW conversion software the interpolation gets done. This can lead to different results with different RAW convertors, depending on how they combine pixels into colours.

RAW in 12 bits will give 4096 levels from dark to light. JPEG has 256 (8 bits) from dark to light.
RAW has more information than JPEG especially in the light area of the spectrum.

So, since RAW has more headroom, you have room to adjust a photo, more than with JPEG. With JPEG you can get to see the steps if you need to adjust exposure or contrast a alot, with RAW the steps are a lot more fine. And in RAW data the white balance has not been adjusted yet, so you can do that later. Nice when you goof up White Balance settings.

So... RAW gives more room for adjustments afterwards. JPEG needs less space, and less processing steps.

zmikers
05-12-2007, 05:43 PM
Coldie, nice explanation. I have a question for you. When you send your RAW photo to photoshop, you have to convert it to 8-bit anyway in order to do any PP. Does this defeat the purpose of shooting in 12-bit originally?

Robert Besen
05-13-2007, 09:13 AM
You can do a fair amount of 16 bit editing in photoshop, and also you have more latitude in your 8 bit raw conversion starting with 12 bits.

tim11
05-13-2007, 04:47 PM
I seem to have difficulty creating lifelike colours from Nikon NEF file using Photoshop CS2 (ver 9.02). I'm not sure if WB was set incorrectly during the shot? But even then I should be able to reset it - so I deducted that the problem is more likely ME. Is there tips somewhere for converting RAW?
Does Nikon RAW editing program give better result than Photoshop?

Norm in Fujino
05-13-2007, 05:59 PM
I seem to have difficulty creating lifelike colours from Nikon NEF file using Photoshop CS2 (ver 9.02). . . . Does Nikon RAW editing program give better result than Photoshop?

I'm not sure about this particular combination, but it's entirely possible. Raw converters (developers) handle different flavors of raw file in entirely different ways, so you often have to try several to find the one you like best. Obviously, the original maker's software should produce the most "loyal" results compared to out-of-camera jpegs, but that's not necessarily the best thing, if the out-of-camera results aren't optimum to begin with.

toriaj
05-13-2007, 10:44 PM
I had the same problem -- extremely desaturated colors in RAW. I even notice it in my LCD, where the shot looks so dull/white that I am tempted to underexpose by at least a stop! I have to remind myself that the exposure meter really is accurate! :rolleyes: (most of the time) I downloaded free Silkypix, and I use the "Color" tool. It's helped a lot.

coldrain
05-15-2007, 02:52 AM
Coldie, nice explanation. I have a question for you. When you send your RAW photo to photoshop, you have to convert it to 8-bit anyway in order to do any PP. Does this defeat the purpose of shooting in 12-bit originally?
If you do the conversion in photoshop itself, you can keep the photo in 16bit mode. If you for instance have a Canon DSLR and use Canon's DPP, it can send the photo to Photoshop too, in 16 bit mode.

If you need to save the photo before you can open it in photoshop, you probably are able to save it as 16 bit TIFF file.

The biggest advantage of RAW has already been used by the RAW convertor by then, though, making the exposure, contrast and white balance to your liking.

The conversion of 12 bit RAW to 16 bit TIFF does alter the information, since in 16 bit photos the spread of dark tones and light tones is totally even, but with sensors the most bits are used for light tones, and very few for dark tones (this has to do with how sensors measure light).
How the real impact is of going from 12 bits RAW to 16 bit image formats I do not know, that is a bit complex to figure out and I do not want to spend a day on that ;).

Another interesting fact:
Our eyes are very sensitive to green. This most probably has to do with nature, and all the shades of green in it... we adapted to our surroundings.
That is why sensors have 2 green pixels and 1 blue and 1 red pixel in a 4-pixel suqare group. This will make the readings of green more accurate, and will give the best results for our eyes.

zmikers
05-15-2007, 04:37 PM
That is interesting about the greens. I know I can keep my photo at 16-bit but in Photoshop. many of the functions are locked until I convert it to 8 bit. Thanks for the explanation though.

coldrain
05-16-2007, 01:50 PM
All functions that actually matter for processing the image (sharpening, colour/contrast/curves and what not all work in 16bit mode. Only functions that have to do with JPEG saving, or changing colour depth are disabled until you change to 8 bits... so it is not a limitation.

zmikers
05-16-2007, 04:21 PM
ok fair enough. I'll have to check it out again. Thanks for the info.