RAW Image Data : Theory

posted by ugaldew, May 23, 2006 4:28 AM — 9 comments

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Introduction

>> What is a RAW file and what makes it so outstanding ?

I really will try to keep it simple When we talk about digital image we have to remember that it is not film anymore, most features of an image like color, temperature , contrast light etc. are just processed bits

So when we take a picture light will generate through the sensor millions of bits and thousands of brightness levels, that will be processed by the camera according to its settings. During this process , most of those bits and levels will only help the camera to understand the image and to process the scene correctly and then they will be lost. The camera will deliver then the process it made , and show us how it interpreted the color , and temperate the light etc

So what is a RAW file? ... well it is that very first impression that light made on the sensor , the unprocessed one ..written in the memory card , with no color or contrast or saturation , and this features will allow us to process the scene our selves ! just like a digital negative





4,096 to 16,384 brightness levels are recorded by the camera and only 256 will be left after the camera processes them
The camera records in a 16 bit mode that will be turned into an 8 bit mode


A raw file however has extra information about how the camera would have process the scene , (sharpening level, contrast and saturation settings, color temperature / white balance, etc ) but it doesn’t affect the image

>> Are the RAW files heavy ?

Yes they are , remember that the camera will delete most bits and brightness levels when it ended processing the image , a RAW file can be 2-6 times heavier than a jpeg picture. The average medium size pics weiths 12MB

>> How can a RAW file be edited ?

The most popular softwares are the ; A) ,Camera Raw converter that is now built into Photoshop CS so you just need PS CS and if you have Photoshop 7 you can download the plug in ,HERE B)Capture One from Phase One, and Iphoto 5 for Macs



you can preview files in OS X Tiger and for Windows theres is a patch you can download HERE

>> Which is the extension of RAW data ?

Most Brands have their own raw image data’s extension , but it works the same

.raf (Fuji)
.crw, .cr2 (Canon)
.mrw (Minolta)
.nef (Nikon)
.orf (Olympus)
.dng (Adobe)

>> What cameras can produce raw ?

here is a list of supported cameras

List

>> Reasons to Shoot Raw ? (Michael Reichmann )

— It holds exactly what the imaging chip recorded. Nothing more. Nothing less. This means the maximum possible of image quality,
— Raw files have not had while balance set.. This allows one to set any colour temperature and white balance one wishes
— color filter array (Bayer) conversion is done on a computer with a fast and powerful microprocessor. This allows much more sophisticated algorithms
— No contrast or saturation has been added to the image so one can have full control of that
— Possibly the biggest advantage of shooting raw is that one has a 16 bit image (post raw conversion) to work with. This means that the file has 65,536 levels to work with. This is opposed to a JPG file's 8 bit space with just 256 brightness levels available.

>> What’s is the difference between JPEG and RAW ?

Bright levels Raw 4000 to 16000 Jpeg : 256
Bits per Pixel (depth) Raw 16bts Jpeg 8bits
The JPEG is a processed image ready to deliver a RAW needs to be processed
JPEG is 6 times lighter and is easier to share than RAW
RAW can be edited at a point where a JPEG can not , such as temperature, color etc

>> When RAW and when in JPEG?

The reason to shot in jpeg is that it is a light and easy to handle file , since jpeg pics are very light , they wont run out you memory card as easy as a raw files do, and in most times they will provide a good quality image for family pics , travel pics, and prints ) , besides that before you can see or print a RAW file you have to process it and convert it to JPEG TIFF] or PSD
You shot in RAW when you want to take care of the whole process, and you really need to use the whole gamma of its opportunities it provides , basically when you are doing art picture , art, important photo sessions , or you need the 12 to 16 bit mode it provides

Well I think we are done with the most important questions about RAW Image Data , If you still have some doubts do not hesitate to ask in this bog or write to ugaldew@yahoo.com

Find more info in :

Michael Reichmann Site

Adobe: Understanding Raw Files(PDF)

Ken Rockwe

Wikipedia

Start practicing with RAW First Edition Steps

I really hope you have enjoyed this first RAW tutorial as much as I did writing it , I think it is a great subject that we should give it a try , the results are really outstanding that will definetively take you to another stage

For any doubt or comment on this tutorial , you can also write to ugaldew@yahoo.com

Miguel Ugalde (ugaldew)