RAW image format

The most common image format amongst digital cameras is JPEG, it's a format which produces relatively small files from large amounts of image data by discarding certain information, JPEG uses a "lossy compression algorithm". The only other common alternative is TIFF, this produces an uncompressed 24-bit per pixel image often in the multiple megabytes, certainly for a 3 megapixel camera in excess of 8 MB per image, not really practical. A little background: each pixel of a CCD can only see one colour, depending on the CFA (colour filter array) placed over the CCD this is either Red/Green/Blue or Cyan/Magenta/Green/Yellow. The cameras internal image processing engine then interpolates colours from the value of neighboring pixels to calculate a full 24-bit colour for each pixel.

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RAW is simply the raw data as it comes directly off the CCD, no in-camera processing is performed. Typically this data is 8, 10 or 12 bits per pixel. The advantage being that file sizes are considerably smaller (D30: 2160 x 1440 x 12 bits = 37,324,800 bits = 4,665,600 bytes), the image has not been processed or white balanced which means you can correct the image, and it's a better representation of the "digital negative" captured. The disadvantage is you can't open these image files with a normal photo package without using an "acquire module" (a plugin, typically TWAIN, which can open / process such images).

RAW image format has actually been around for quite a while, Canon had a RAW format back in the old PowerShot range and more notably on the Pro 70, all of Kodak's DCS Pro series shoot in a proprietary RAW format (despite the TIFF extension), Nikon's D1 also has a RAW format. Canon have (thankfully) resurrected RAW format for the EOS-D30 and G1. The new RAW format stores 10 or 12 bits (in the case of the EOS-D30) of data per pixel which is then losslessly (like a ZIP file) compressed, obviously the success of this compression depends on the image content, we found the average size of a D30 RAW file to be about 3.0 MB (certainly an improvement on it's 9.1 MB 8-bit TIFF or 18.2 MB 16-bit TIFF equivalent).

Supplied with the D30 is a TWAIN acquire module (driver) which allows you to open RAW (or D30 JPEG) files from any TWAIN compatible photo package (Photoshop, Paint Shop Pro, etc. etc.). It's actually the very same driver used for other Powershot products.

This window allows you to select the files to be imported, these can be on your local hard disk (or any attached file system device) or on the card in-camera via USB. Clicking on an image (or group of images) and select "Set RAW Param" displays the window shown below:

Which allows the modification of parameters such as white balance, sharpening, contrast and colour saturation which can be left as default (camera settings), set individually or for the group of images. White Balance can even be manually "picked" from a white area on the image. The EOS-D30 TWAIN allows for linear import of the image at 16-bits per channel, this image has not been correct in any way and is simply an interpolation of the colours from the RAW file to 36-bits per channel (example below):

RAW acquired normally
1,401 KB JPEG (8-bit per channel)
RAW acquired "Linear"
17,718 KB LZW TIFF (16-bit per channel)
966 KB JPEG (8-bit per channel)

One thing I think is missing is an exposure compensation slider which would allow you to adjust the exposure +/- 2 EV, this should be easily possible and would allow you to get more out of the fact that the RAW file itself contains 12-bits of information (without having to acquire and adjust huge linear files as above). This is a standard part of Kodak's acquire modules, I'd like to see Canon consider it when updating their software. I'd also hope they could speed up acquisition in an update too, it currently takes about 40 seconds to acquire an image (on my dual processor workstation).

Frame the main window you can also extract shooting information from an image (RAW or JPEG):

File Name CRW_8961.CRW
Camera Model Name Canon EOS D30
Shooting Date/Time 10/04/2000 1:50:46 PM
Shooting Mode Program AE
Tv (Shutter Speed) 1/350
Av (Aperture) 6.7
Metering Mode Evaluative
Exposure Compen. 0
ISO Speed 100
Lens 28.0 - 70.0mm
Focal Length 55.0mm
Image Size 2160 x 1440
Image Quality RAW
Flash Off
White Balance Daylight
AF Mode One-Shot AF
Focusing point [ Left Center Right ]
Parameters Contrast Normal
Sharpness Normal
Color saturation Normal
File Size 3344 KB
Serial Number 0-8961
Drive Mode Continuous shooting
Macro Off
Camera body no. 0xxxxxxxx
Custom Function Settings
01:Long exposure noise reduction 0:Off
02:Shutter button/AE lock button 0:AF/AE lock
03:Mirror lockup 0:Disable
04:TV,AV and exposure level 0:1/2-stop
05:AF-assist light 0:On(Auto)
06:Shutter speed in Av mode 0:Auto
07:AEB sequence/auto cancellation 0: 0 => - => +/Enabled
08:Shutter curtain sync 0:1st-cutain sync
09:Lens AF stop button Fn, switch 0:AF stop
10:Auto reduction of fill flash 0:Enable
11:Menu button return position 0:top
12:SET button func, when shooting 0:Default(no function)
13:Sensor cleaning 0:Disable

Below we've provided a few samples of the same RAW file acquired with different "RAW parameters" to try to give an impression of why RAW is useful and allows for flexibility. All images were acquired into Photoshop then re-saved with a quality level of 12.

White Balance correction

Contrast: Normal, Saturation: High, Sharpness: Normal

White Balance: Auto White Balance: Daylight White Balance: White Point

Auto white balance had a slight blue cast, Daylight was the most accurate closely followed by manual white point.

Contrast / Saturation combinations

White Balance: Daylight, Sharpness: Normal

Contrast: Low
Saturation: Low
Contrast: Normal
Saturation: High
Contrast: High
Saturation: High

I was most comfortable with Saturation High, Contrast Normal, though of course the great thing about having the RAW data is you can decide on a per image basis (if you can stand the wait).


White Balance: Daylight, Contrast Normal, Saturation High

Sharpness: Low Sharpness: Normal Sharpness: High
  Sharpness: Low &
Photoshop Unsharpen Mask 128%, Radius 0.6 pixels, Threshold 2 levels

In these samples I threw in another option, acquiring with Normal sharpening then sharpening the image with an Unsharpen Mask.


This is an update to the originally published review, we had a lot of interest from our forums questioning whether it was worth shooting RAW and what (if any) image quality advantage there is (understanding there's always more 'headroom' in a RAW because it's recorded as 12-bits of data per pixel and that you can apply white balance, sharpness, saturation and tone settings later).

Our findings are that up to ISO 400 there's little difference between RAW and JPEG images, obviously if you have the storage (and time to convert the images later) then RAW provides more flexibility, but it also limits the number of frames you can shoot on a single card and the burst abilities of the camera. At ISO 800 and 1600 it appears that the noise introduced into the image generates increased noise when shot in JPEG rather than RAW, this is probably because of the way the JPEG algorithm works, thus in nearly every test there was always less green channel noise in RAW images.

ISO 100

ISO 100 RAW, available as 8-bit TIFF (9,124 KB)
ISO 100 JPEG, original JPEG (1,027 KB)

ISO 200

ISO 200 RAW, available as 8-bit TIFF (9,124 KB)
ISO 200 JPEG, original JPEG (1,125 KB)

ISO 400

ISO 400 RAW, available as 8-bit TIFF (9,124 KB)
ISO 400 JPEG, original JPEG (1,276 KB)

ISO 800

ISO 800 RAW, available as 8-bit TIFF (9,124 KB)
ISO 800 JPEG, original JPEG (1,493 KB)

ISO 1600

ISO 1600 RAW, available as 8-bit TIFF (9,124 KB)
ISO 1600 JPEG, original JPEG (1,799 KB)

High ISO "green channel noise" comparison

(Please refer to linked images above for originals)

Red Channel Blue Channel Green Channel

Red Channel Blue Channel Green Channel

Red Channel Blue Channel Green Channel
ISO 1600 RAW

Red Channel Blue Channel Green Channel

I think you can see from the samples above that although there's little difference between in the red and blue channels between JPEG and RAW but that the noise visible in the green channel of JPEG images was almost none existant in RAW images. The conclusion? If you've got the storage and you're shooting at ISO 800 and 1600 then you'll get better results shooting in RAW.