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Canon EOS 20D

By: Shawn Barnett and Dave Etchells

Slightly smaller and lighter upgrade brings greater speed and ease of use along with higher res and lower image noise.

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Page 11:Image Storage & Interface

Review First Posted: 08/19/2004, Update: 11/19/2004

Image Storage and Interface

The EOS 20D utilizes CompactFlash (Type I and II) memory cards as its image storage medium, which should never be removed from the camera while in use. (Removing a card while the camera is still writing to it could cause permanent damage to the card.) The EOS 20D does not ship with a memory card, so you'll want to purchase a large capacity card right away. I'd recommend picking up at least a 512MB card for starters, given the EOS 20D's large, 3,504 x 2,336-pixel maximum resolution. The table below shows card capacities and approximate compression ratios for the various file sizes and types, based on a 1GB memory card. Like the 10D before it, the 20D is fully compatible with IBM MicroDrives and other Type II CompactFlash devices.

The EOS-20D supports the FAT32 directory structure. (FAT stands for File Allocation Table, and FAT32 indicates that these newer cards use a 32-bit File Allocation Table. In general, digicams made before 2003 supported only FAT 16.) The larger address space provided by FAT32 is necessary for managing high-capacity memory cards of 2GB or greater capacity. This hasn't been an issue until now, but current CF cards with capacities as high as 8 GB require FAT32 support to use them.

Image Capacity vs
1GB Memory Card
Fine Normal
3504 x 2336 Images
(Avg size)
5.4 MB
2.7 MB
5:1 9:1
2544 x 1696 Images
(Avg size)
3.0 MB
1.5 MB
4:1 9:1
1728 x 1152 Images
(Avg size)
1.6 MB
4:1 6:1 
(Avg size)
5.0 - 13.5 MB


The RAW mode listed above deserves some explanation. This is a format that records all the data from the sensor, exactly as it comes from the A/D conversion process. It is lossless compression, meaning that the file is reduced to a smaller size, but without losing any data in the process. It thus preserves all the original data from the sensor, but is nevertheless much more compact than an equivalent TIFF file. Depending on the subject content, RAW files will compress more or less. In our use of the camera, we saw compression ratios ranging from 1.8:1 to 5:1. Most images will likely come out around 2:1, for a file size of a bit more than 12 MB.


Download Speed

The 20D has a USB 2.0 port for rapid file transfers to the host computer. Note that the 20D won't auto-mount on your computer's desktop, but rather needs to be accessed either by the Canon EOS Viewer Utility (Windows and Mac), or by the Windows Image Assistant (drivers for which are included on the solutions disc that accompanies the camera.) I tested download times on my Sony VAIO desktop machine, running Windows XP. Downloads via Windows Image Assistant (WIA) were fairly fast, at 1208 KB/second, but it's important to note that WIA only recognizes JPEG files, and so can't be used for transferring RAW images. As fast as WIA seemed to be, transfers through Canon's own Image Viewer utility were much faster, at 2,190 KB/second. This is very fast, even among cameras with USB v2.0 interfaces.


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