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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 neighbouring pixels to calculate a full 24-bit colour for each pixel.

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 (2048 x 1536 x 10 bits = 31,457,280 bits = 3,932,160 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 G1 RAW file to be about 2.8 MB (certainly an improvement on it's 9.7 MB TIFF equivalent).

Supplied with the G1 is a TWAIN acquire module (driver) which allows you to open RAW (or G1 JPEG) files from any TWAIN compatible photo package (Photoshop, Paint Shop Pro, etc. etc.). It's actually the very same driver used for the EOS-D30.

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. Those who are observant will have noticed the grayed out "Linear" checkbox, this is reserved for the EOS-D30 which allows for linear import of a 16-bit per channel file (no gamma correction). G1 images can only be acquired at 8-bits per pixel.

One think I think is missing (and this is also true when importing EOS-D30 images) 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 10-bits (or 12-bits in the case of the D30) of information. 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 24 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_0483.CRW Digital Zoom None
Camera Model Name Canon PowerShot G1 Image Size 2048x1536
Shooting Date/Time 09/27/2000 12:02:28 PM Image Quality RAW
Shooting Mode Program AE Flash Off
Tv( Shutter Speed ) 1/500 White Balance Auto
Av( Aperture Value ) 5.0 AF Mode Single
Metering Mode Center-weighted averaging File Size 2792KB
Exposure Compen. 0 Serial Number 0-0483
ISO Speed Auto Drive Mode Single-frame shooting
Lens 7.0 - 21.0mm Macro Off
Focal Length 18.8mm Parameters Contrast Normal
Sharpness Normal
Color saturation Normal

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 resaved with a quality level of 10.

White Balance correction

Contrast: Low, Saturation: High, Sharpness: Normal

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

Both the Auto and preset Daylight White Balance's gave a green cast, by far the best white balance was achieved using the White Point "dropper" (reference point taken from the not over exposed white area of the boat's hull).

Contrast / Saturation combinations

White Balance: White Point, Sharpness: Normal

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

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


White Balance: White Point, Contrast Normal, Saturation High

Sharpening: Low, Normal, High, Low + Photoshop Unsharpen

Sharpness: Low Sharpness: Normal Sharpness: High
  Sharpness: Low &
Photoshop Unsharpen Mask 120%, Radius 0.8 pixels, Threshold 2 levels

In these samples I threw in another option, acquiring with Low sharpening then sharpening the image with an Unsharpen Mask, I found this to give the best results, though your mileage may vary.

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