*.THM files in RAW mode

[Dr. Kelp]

I've got an EOS 10D, which I dearly love. When shooting in RAW mode, I get a second copy of each image that has the extension .THM. These are tiny little images with extremely low resolution and I have no idea what purpose they serve, if any. I find them annoying as I just end up deleting them.

Can anyone tell me anything about what purpose they serve, and is there a way to stop the camera from saving them?

Thanks.

[PacAce]

They are thumbnails of the raw file. Makes it easier to display them in programs such as EVU instead of converting the raw file each time they are displayed. They also contain EXIF information that is not stored in the RAW files themselves so unless you really don't care about the EXIF info, I wouldn't go deleting them all if I were in your shoes. I personally keep every one of these .THM files. AAMOF, on my XP system, I have my registry set up to treat .THM files as JPEG files so that I can see these file in thumbnail mode via Windows Explorer. That makes it easy for me to see exactly what the RAW files are in Explorer without me needing to open them in EVU or any other image editing program.

[tim]

EXIF info is stored in RAW and CR2 files. My 300D created the THM files, I deleted them, and I still had full EXIF.

There's a free little program around that lets Windows preview RAW/CR2 files, plus IrfanView can view them too, so there's no need for THM files. It's on a thread somewhere around here, if you can't find it PM me and i'll look at home later.

[sykocus]

I used this guide to have windows show thumbnails for my raw files. it only works in windows XP though.

http://www.suodenjoki.dk/us/productions/articles/raw_thumbnail.htm

[robertwgross]

EXIF info is stored in RAW and CR2 files. My 300D created the THM files, I deleted them, and I still had full EXIF.

Are you absolutely sure of that? Full?

---Bob Gross---

[RichardtheSane]

The RAW contains basic Exif.

But the THM has some extra stuff in it.

[robertwgross]

The RAW contains basic Exif.

But the THM has some extra stuff in it.

Yes, that is the way mine always was.

Apparently Tim's is different.

---Bob Gross---

[sykocus]

Mine's more like Tim's. It could be different with different camera model's. I have 300d like Tim.

[Huckaback Photo]

Bob
totally agree with you on this one.
realised some time ago different people seem to have various amounts of info shown in there exif
file per image.
without these small (info files if you like) some info is not with the raw file.
I believe about 29 lines of info to be the full list ???
but I guess this may well vary with cameras etc. etc. Just checked this on a raw shot with 1D mk 2

A useful little bit of software so raws can be displayed as thumbnails with windows is DP magic comunity edition.
hope this helps.
personally i would not delete these info files

http://www.dpmagic.com/

Martin (Huckaback Photo)

[tim]

Just had a check, the EXIF in a RAW from my 300D has shutter speed, aperture, EC, metering mode, flash fired (yes/no), focal length, ISO, exposure mode (eg aperture priority), and a couple of useless fields. It's possible the thm file has more information in it, but none that i've ever wanted to know.

[pcasciola]

It's ok, Tim, we all make mistakes. ;)

I might be wrong, but I think some of the other dSLRs have none of the exif in the RAW. Not sure about the 10D, though.

[robertwgross]

There is a point here, gang. The point is that EXIF may be a standard, but the implementation of the standard is inconsistent among different brands and different models.

Although a .THM file is unnecessary to some users, it does carry EXIF information that is of value through some programs. Just because the information is there, you can choose to ignore it.

In my view, the .THM files were so tiny, as compared to the main file, that it made little difference in file capacity on any storage media. So, I figured I would keep them.

---Bob Gross---

[tim]

It's ok, Tim, we all make mistakes. ;)

I made a mistake? Never?!

What exif information is available in a thm file that's not in the RAW?

[PacAce]

I made a mistake? Never?!

What exif information is available in a thm file that's not in the RAW?
The first attachment is a screen print of the EXIF info in the CRW file.
The second attachment is a screen print of the EXIF info in the THM file.

BTW, if the two files are together, the program you are using to view the EXIF info will merge the info from both files. So see the their respective EXIFs individually, you have to put them in separate folders.

[sykocus]

what program is that? I'd like see what it looks like with a file from a rebel.

[PacAce]

what program is that? I'd like see what it looks like with a file from a rebel.
I used ExifPro Image Viewer from here: http://www.exifpro.com/

There's a none pro version here: http://home.pacbell.net/michal_k/exif_v.html

Don't forget to put the THM and the CRW files in different folders to see the actual EXIF info for each.

[tim]

PacAce, I think the problem you're having is with your sofware. Photoshop CS file browser shows the list of information I made above from a CRW file, I think the software you're using just isn't CRW compatible. I delete thm files so there's no chance it picked it up from one of them. The THM file does have more information, though I can't see any that i'd find useful.

[pcasciola]

I made a mistake? Never?!

What exif information is available in a thm file that's not in the RAW?
Subject distance for one, and I believe the Canon Makernote data as well, which includes custom function settings, etc.

[PacAce]

PacAce, I think the problem you're having is with your sofware. Photoshop CS file browser shows the list of information I made above from a CRW file, I think the software you're using just isn't CRW compatible. I delete thm files so there's no chance it picked it up from one of them. The THM file does have more information, though I can't see any that i'd find useful.
Tim, did you delete the cache and rebuild the thumbnail in PSCS?

[sykocus]

The first attachment is a screen print of the EXIF info in the CRW file.
The second attachment is a screen print of the EXIF info in the THM file.

BTW, if the two files are together, the program you are using to view the EXIF info will merge the info from both files. So see the their respective EXIFs individually, you have to put them in separate folders.

I got similar results for the seperate raw file with that program, but couldn't get it to see the thm file by it self. I tried something I had started last night though. I took 2 pictures in RAW format on 2 different CF cards. On 1 I opened and converted it with the thm still on the card. With the other I deleted the thm file then opened and converted it. The data for them is the basically the same.

(I overlapped the screen shots to save space)

[pcasciola]

I got similar results for the seperate raw file with that program, but couldn't get it to see the thm file by it self. I tried something I had started last night though. I took 2 pictures in RAW format on 2 different CF cards. On 1 I opened and converted it with the thm still on the card. With the other I deleted the thm file then opened and converted it. The data for them is the basically the same.

(I overlapped the screen shots to save space)You are also missing a lot of EXIF data there. The basic stuff is there in the RAW, yes, and many programs cannot read any of it as in PacAce's case, but the RAW is NOT a complete set of Canon EXIF information. Whether or not the missing information is of any value is another argument but the fact remains the THM has more EXIF information than the RAW alone.

BTW, if you want to see the EXIF information in a THM, rename it to JPG.

[defordphoto]

On a 10D you lose whatever Cfn settings you had. Everything other than Cfn settings is there, with or without the .thm file.

Nevertheless, we're talking 11-14Kb per photo. Not a big deal when drive space is about 50-75 cents a gig or so.

[pcasciola]

On a 10D you lose whatever Cfn settings you had. Everything other than Cfn settings is there, with or without the .thm file.Subject distance is lost as well, along with more of the Canon Makernote data aside from custom functions.

[tim]

Tim, did you delete the cache and rebuild the thumbnail in PSCS?

Nope, I can give it a go if you'd like. I tend to delete thm files before I start PS CS, can't guarantee that in this case though.

[sykocus]

You are also missing a lot of EXIF data there. The basic stuff is there in the RAW, yes, and many programs cannot read any of it as in PacAce's case, but the RAW is NOT a complete set of Canon EXIF information. Whether or not the missing information is of any value is another argument but the fact remains the THM has more EXIF information than the RAW alone.

BTW, if you want to see the EXIF information in a THM, rename it to JPG.

Could but, but it's difficult to say for sure. Both the CRW with THM and the plain CRW ended up with the same amount of data. Photoshop seems to only read some of the EXIF. (Someone already mentioned that EXIF impementation isn't completely standardized). And the EXIF viewer wasn't able to get any EXIF from the plain CRW (which we know is there).

Also about the subject distance info. I read that that was a feature of ETTL-II and that it only worked with certain lenes.

[tim]

Could but, but it's difficult to say for sure. Both the CRW with THM and the plain CRW ended up with the same amount of data. Photoshop seems to only read some of the EXIF. (Someone already mentioned that EXIF impementation isn't completely standardized). And the EXIF viewer wasn't able to get any EXIF from the plain CRW.

Also about the subject distance info. I read that that was a feature of ETTL-II and that it only worked with certain lenes.

Yeah, could be the EXIF's there and PS isn't reading it.

Re distance info, we're talking about recording it, not using it, though you're correct that ETTL II (not 1) uses it when the lens provides it.

[Jon]

OK. I took a RAW from my D60, moved the THMs into one directory and the CRW into a second using Windows Explorer (so no way ZB could get the info). I then viewed the "Properties" for the CRW using ZB 4.6. The THM files weren't visible in ZB. I shut down ZB, moved the THMs into the same directory as the CRWs, reopened ZB, refreshed, and the Properties displayed were the same. So whatever's there, Canon utilities see it with or without the THM.

BUT I opened a THM and the corresponding CRW with EXIFReader 3.0 and the information displayed was in markedly different format, and some of the named fields in the two files differed in value. For instance the ISO setting was 200 according to the THM but 100 in the CRW. IIRC, 200 was te correct value. The CRW didn't show (identified) values for shutter speed or aperture, which were listed in the THM. BR's EXIF Extractor 0.9 wasn't able to acquire any from either. So however the information is stored in the CRWs, it appears Canon knows how to get full EXIF info without needing the THM, but other programs can't read it.

[defordphoto]

Subject distance is lost as well, along with more of the Canon Makernote data aside from custom functions.

Yeah I missed those. Thanks.