I'm Michael Suodenjoki - a software engineer living in Kgs. Lyngby, north of Copenhagen, Denmark. This is my personal site containing my blog, photos, articles and main interests.


Viewing Camera RAW Thumbnails in Windows Explorer Viewing Canon Raw .CRW and .THM file extensions in Windows Explorer

Updated 2011.02.06 13:21 +0100

Ikke tilgængelig på Dansk


This article describe some information from the internet that I've found useful for previewing Canon Camera Raw .crw and .thm file extensions in the Windows Explorer.

This only works in Windows XP (see updates below for .CR2 files and Vista support).

The information is this article is not my own invention but is a creation of Dmitriy Belenko and Mike Fried and has been collected from the following two sources:



The Windows Explorer do not pr. default show you Canon .crw and .thm files when you go into the thumbnail view mode. This is cumbersome if you just want to a a little preview while organizing (copy/pasting) your photographs.

Method 1: Using a dll to preview .crw files

Dmitiy Belenko wrote this little plug-in for Windows XP. It will work with XP only (GDI+ is required), so W2K users please don't bother downloading.


Here's the actual plug-in. Disclaimer, use this software at your own risk. There are no warranties on it whatsoever. It works for me as well as for some folks at work, but there's no guarantee it will work for you. Even if it blows up your computer I shall not be responsible.



Installation is simple, just unpack the zip file, copy the DLL to your windows or system32 directory and do the following from the command line:

regsvr32 <path_to_the_directory>\crw_thumbnailer.dll 

Replace <path_to_the_directory> with the actual path.

Uninstallation is also simple, just run the same command with /u switch.

From the very moment you install the thing you'll have your CRW files thumbnailed if you select Windows XP "Thumbnails" view mode.

Method 2: Hacking the registry to tell Explorer to treat .thm as jpeg files

The THM files are JPEGs (rename a .thm to a .jpg and you get a preview thanks to IE). Why can't I just use the image extractor used by JPEGs? Why not indeed? It turns out that the IE thumbnail extractor will read THM files, and correctly parse the JPG image out of it.

Yes, it is a registry hack. Basically, we tell the Windows Explorer/Shell to use the TridentImageExtractor class ({7376D660-C583-11D0-A3A5-00C04FD706EC}) to handle the ImageExtractor interface ({BB2E617C-0920-11D1-9A0B-00C04FC2D6C1}) on the .thm extension.

This registry hack won't rotate the files for you... I guess that IE doesn't understand whatever rotation information Canon embeds into the file.

Remember, you tweak your own registry at your own risk. I'm not responsible if you mess things up. This is supposed to work with Windows 98 and above, but I only tried it on Windows XP.

Anyway, here's the contents of the .REG file:

Windows Registry Editor Version 5.00 


--End of THMPreview.reg-- 


If launching notepad and typing all that in (all of the things in the []s should be on the same line) is scary, I'll make it easy for you. Just download:


To give fair credit where credit is due, the article which inspired me to try this in this way was http://www.tech-pro.co.uk/howto_011.html