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The RAW digital image format
Why you should consider using your camera's raw format
--better quality, nothing is lost, and you can reprocess the images years later to get even better results
Higher quality digital cameras often have a raw image format available in addition to the normal JPEG and TIFF. Keith has often had people come along to his courses who have found the extra complexity involved in using raw images off putting. In general, Keith -only- uses raw format on his digital cameras. He presents here some of his reasons. The conversion software discussed here is mostly Adobe Camera Raw which is part of Photoshop. There are links to other methods as well.
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Topics The What's New Page gives a quick overview of the hundreds of pages of articles and picture on this site. This article was first written in 2004, and reviewing it at the end of 2006 I found no reason to change any of the details of what I said. Rather than change it, I've added one or two notes that show new developments. |
This page is part of the Articles section of our Info and Resources feature
What is the Raw format
Digital camera image sensors create an image from literally millions of tiny light sensing areas on a silicon chip. There are two main types (CCD and CMOS) but all you really need to know is that the image is built up from individual pixels. (CCD/CMOS comparisons, and a useful article on sensor designs)
Each light sensor is receptive to a broad range of colours and has a minute coloured filter in front of it. There are usually three different colours (red, green and blue). Since we see green best the filters are in a particular pattern (one called a Bayer pattern is common) with more 'green' pixels
Some manufacturers have variations on this (Fuji, Sony), and Foveon make chips with each pixel location sensitive to all three colours. Whatever techniques is used, the camera needs to take the raw image data and save it as a picture file.
Bayer pattern
The actual sensor can provide data at 12 to 14 bits per pixel (4096 to 16,384 levels of intensity) This is reduced to 8 bits per colour in a JPEG file (24 bits total, 8 per colour R,G and B) The complete unreduced data is stored in a raw format file.
The camera has a lot of other information available when a picture is taken. Along with the date and time it records shutter speed, aperture and its estimate of the white balance setting and other pertinent data. This is recorded with any picture.
To produce a JPEG or TIFF file, the computer inside the camera has to do quite a lot of calculations on the raw data to produce a picture file. These are carried out once, and the result is what you see when you open the file in a picture editor program. With a raw format file these calculations are not done and all of the original data is saved to the raw file.
The EXIF data for the picture of Old John below.
How do you use raw files
Camera manufacturers will provide special software to read and convert raw files. This is in effect using your computer to do the calculations that the camera would have done if you'd saved in JPEG. Things such as sharpening, colour settings and contrast all take place during the conversion.
Sadly, most camera manufacturers are much better (it is hoped) at making cameras than writing software for you to use. This is where specialist conversion programs and plugins for popular image editing programs come in.
The examples below are using Photoshop CS to do a conversion of an Olympus E20 raw file. The picture is the same one used in the converting colour to black and white article elsewhere on the site. There is a collection of info on other raw conversion programs at the end of this article.
Old John, Bradgate Park, Leicester
With Photoshop CS you will get the raw import dialogue if you open up a raw image from one of the supported cameras (there are regular updates to cover new models)
Notice the ORF suffix to the file name, signifying an Olympus raw file.
The picture opens up in a preview window with lots of settings. This is not a tutorial on the CS raw import feature, so I'll just point out a few of the things you can do when importing.
Resizing
The native resolution of the camera gives a 2572x1920 pixel image
Since we have the original sensor data to work with, there are mathematical techniques we can apply to scale the image certain amounts and get noticeably better results than by normal resizing. If you are going to enlarge your image, then this is the best place to do it.
Note added 2005
That was what I did until fairly recently. Photoshop now has improved sharpening algorithms that can give better results. I've written a separate article on Resampling of raw camera files with some examples and details of my current workflow - As I say there, don't be afraid to change your workflow if a better way comes along.
White balance
You can choose to use the data suggested by the camera, or apply your own settings.
Chromatic aberration
A noticeable defect when the wide angle teleconverter was fitted to the E20
By adjusting the sliders much of the effect can be removed.
Look at the following (much magnified) samples -- before and after correction.
Top right hand corner
Mid right hand side
Quite a difference. Even the expensive Canon 16-35mm 2.8L zoom that I use on my Canon 1Ds has a bit of chromatic aberration at its wider settings and benefits from a slight adjustment in many shots.
What are the advantages of raw format.
- All your conversions are done on a fast powerful computer at your convenience.
- Images can be 'fixed' in ways which would be very difficult without the raw sensor data.
- You get the full range of data from the sensor.
- Without sharpening or compression you have not 'lost' any data.
- You can change your mind about some of the picture settings after you have taken it.
September 2006 -- I just reprocessed some of my raw files from 2004 for some new prints - some were noticeably better, making the difference between what would make a good 27"x17" or not. Image processing software is getting more and more powerful, I'm really glad I have all my many thousands of images in their original raw format!
Is there a downside?
- Raw files are bigger
- JPEGs are quick and easy to use.
- Special software is required to do the conversion.
- Not all cameras support raw formats and may offer reduced functionality when using raw.
Summary
Raw files are essentially 'digital negatives', or perhaps more accurately 'digital exposed but undeveloped film'. You get to carry out much of the work that the camera would do, on your own computer. You can decide how you want the image to look. If new software comes out with revolutionary new capabilities, you can go back and do a new conversion (see Keith's review of DxO Optics Pro for an example of this). The added dynamic range (16 bit files) gives you much more flexability in subsequent editing of images (particularly in bringing out detail in shadows) Sure, the files are bigger, but disk and card costs are getting cheaper by the minute.
(11/04) Just about every manufacturer uses their own internal format for raw files. This may well cause problems in the future in reading 'old' files. I happily endorse Adobe's efforts to introduce an open format for raw files and hope that manufacturers can look beyond some of their perceived short term advantages for the benefit of us all.
(12/06) More and more cameras are providing raw support. Since writing this article I've not once shot jpeg images with my Canon 1Ds
Other views
With good conversion software I leave my cameras set at raw most of the time. However I should recount a photo job (in 2004) where I had 500 items of men's clothing to shoot for a trade catalogue. The images were going to be cut out from the background and printed at 30-40mm high. The lighting was consistent and full colour accuracy was not required. 8 bit JPEG files were more than good enough for the client's needs - and took up far less space. (2006 - I'd use raw and do a bulk conversion with Photoshop :-)
There is often debate about the merits of RAW shooting, and I've heard some utter nonsense on both sides. The following quote points out two differing views and is from Farzal Majid's article on the Nikon D70 raw format (NEF)
"The first is people for whom the creative moment is when you press the shutter release, and who do not want to be involved in post-processing. This was Henri Cartier-Bresson's approach. This group also includes professionals like wedding photographers or photojournalists for whom a streamlined workflow is an economic necessity (even though the overhead of a RAW workflow diminishes with the right software, it is still there).
The second type of users is composed of perfectionists who want complete control over the image. In the age of film, they would spend long hours in the darkroom getting their prints just like they want them. This is the approach of Ansel Adams. The RAW file is the negative."
I guess my own preference tends to the second for my landscape work ;-)
Oct 2005 - I've written an article about the technical image processing and resizing issues that I came across when producing 29 prints (up to 78"x43") for a large exhibition of my work. One more reason I'm glad I have the original RAW files to go back to if need be.
Raw conversion resources
Some software to get you started...
- http://store.adobe.com/products/photoshop/cameraraw.html
Feature list from Adobe about the RAW importer mentioned in the article (Mac/win)
Also has downloadable pdf files about RAW capture and other image processing related info - http://www.dxo.com/en/photo/raw_engine/default.php
The new raw file processing software from DxO - Keith has written a lengthy review (11/04) and now uses it for some of his best work
See also Keith's review of DxO 3.5
A new version (4.2) is now (Mar 07) available, and we have a comprehensive DxO Optics Pro review - http://www.bibblelabs.com
Bibble software (Mac/win) Trial version available - http://www.c1dslr.com/
Capture one is renowned for its workflow management. Used by many professionals who shoot a -lot- of raw images. (Mac/win)Trial versions available - http://www.breezesys.com/
Breezebrowser (win). Trial version available - http://www.cpicture.de/en/index.html
cPicture (win). Free LE version available - http://www.frostyplace.com/dcraw/index.html
dcRAW for OSX a very good linear raw file converter, based on the linux command line utility dcRAW. - http://www.iridientdigital.com/products/
RAW Developer (Mac) Powerful raw conversion s/w - lots of adjustments and settings to play with. Trial version available.
Raw conversion techniques
- http://visual-vacations.com/Photography/hybrid_raw_conversion.htm
Making use of linear raw conversions to improve dynamic range. - http://www.creativepro.com/story/feature/21351.html
Alternative to creating profiles for getting accurate colour with CS raw import, by Bruce Fraser (see his excellent book on colour management) - http://rawformat.com/
A site devoted to an open imaging RAW format standard. Lots of info about new developments. - http://194.100.88.243/petteri/pont/How_to/o_RAW_workflow/_RAW_workflow.html
Very good article on when to use raw formats, and how to incorporate them in your workflow - http://www.russellbrown.com/tips_tech.html
Dr. Brown's Image processor. Javascript utility for automating raw processing in PS CS. Includes tutorials - Real World Camera Raw with Photoshop CS - good book by Bruce Fraser (see our books section)
- http://www.normankoren.com/digital_tonality.html
A very comprehensive article of getting the best quality and tonality from your digital images. Part of a site that should be in any digital photographers bookmarks. - http://www.adobe.com/digitalimag/ps_pro_primers.html
Collection of useful articles and papers from Adobe, including lots more about the Camera Raw import facility in Photoshop. - http://fors.net/scripts/ACR-Calibrator/
A free Adobe Camera Raw (ACR) calibration script. Generates calibrations settings if you use a picture of a colour chart.
Keith has written more about it's use when calibrating cameras in a review of using the SG ColorChecker Card from GretagMacbeth - http://www.adobe.com/products/dng/main.html
Digital Negative or DNG is an open format for raw camera files. Hopefully this will make it easier to use raw format and address the problems of how you are going to be able to read the current proprietary files in years to come. - http://owl.phy.queensu.ca/~phil/exiftool/Canon_raw.html
Far more information about what lives in a raw file than you probably wanted to know. - http://www.cs.pdx.edu/~cklin/demosaic/
Want to write your own converter? Some info on demosaicing algorithms and other factors affecting raw camera file decoding.
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