Canon 10D User Guide (en)

Create a new thumbnail image for the main window and save to each 
The quality of images in the main window improves and images redraw 
themselves more quickly.
With all the images selected, select the [File] menu   
[Add thumbnail to image and save].
Improving the Quality of an Image in the Main Window
The quality improves the most when [Large thumbnail] 
 is selected. 
When [Medium thumbnail] or [Small thumbnail] is selected, the 
improvement in quality may be hard to tell due to its size. The quality 
also improves for JPEG and TIFF images.
The extent of the improvement in quality
A large number of images may take some time to add.
Select the image for which you want to check the 
shooting information.
Select the [File] menu   [Info].
The image information window appears.
Checking Image Shooting Information
Switching displays
If a different image is selected in the main window when the image 
information window is displayed, the shooting information for that 
image will be displayed.
Difference with the [Thumbnail with information]
Detailed shooting information for each image is displayed in the 
image information window. However, if you want to only check the 
main shooting information, you can check it for each image in 
[Thumbnail with information] 
Convenient uses in the main window