removed photos from DSLR and moved back - Canon DSLR can't recognize photos

I have removed card/RAW photos from Canon DSLR, renamed photos and without changing them moved back to card and inserted camera. Canon DSLR can't recognize photos...It can't play them. Why? Anybody can explain this?

Thanks!

This inability to display files moved TO a Canon digital camera has always been true! I first encountered this with the Canon G2 back around 2002. Apparently there is an internal (on the memory card) file which has an entry which the camera looks at for each photo that it displays; no entry, no display of that file. That's the way it was explained to my by someone at Canon's tech support.

In fact, you cannot even copy a photo file, alter it with a program like Photoshop or Paint Shop Pro, and copy that file back to the memory card, as the entry in the internal file does not point to the altered version of the file!

Wilt wrote in post #18264051
This inability to display files moved TO a Canon digital camera has always been true! I first encountered this with the Canon G2 back around 2002. Apparently there is an internal (on the memory card) file which has an entry which the camera looks at for each photo that it displays; no entry, no display of that file. That's the way it was explained to my by someone at Canon's tech support.

In fact, you cannot even copy a photo file, alter it with a program like Photoshop or Paint Shop Pro, and copy that file back to the memory card, as the entry in the internal file does not point to the altered version of the file!

I see! Why did they at Canon do that? What is the reason behind it?

No explanation given for rationale. Just is that way

I think it is a result of the Design Rules for Camera Filesystems specification. This is a specification from one of the Japanese Camera manufacturers trade associations, the names seem to change periodically, that allows memory cards to be awapped between different cameras without ill effect. Although a Japanese specification it seems to have been adopted worldwide by most manufacturers. It is why all cameras use the same basic folder structure. As I understand things part of this specification basically says if you did not create the file, then you do not touch the file, even if it is in "your" location within the file structure.

Canon as one of the major players tend to stick pretty rigorously to the rules, while some smaller and non Japanese manufacturers may not be quite so rigid.

Alan

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Wilt wrote in post #18264051
Apparently there is an internal (on the memory card) file which has an entry which the camera looks at for each photo that it displays; no entry, no display of that file. That's the way it was explained to my by someone at Canon's tech support.

In fact, you cannot even copy a photo file, alter it with a program like Photoshop or Paint Shop Pro, and copy that file back to the memory card, as the entry in the internal file does not point to the altered version of the file!

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This sounds like the perfect kind of thing for Magic Lantern to override.

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Tom Reichner wrote in post #18264453
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This sounds like the perfect kind of thing for Magic Lantern to override.

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Tom there are very good reasons why the camera systems won't touch files it did not create, and that is the screen. Attempting to load an image that is the wrong size and shape could well crash the camera, with a minor potential to actually brick it. A simple buffer overrun in a system that is not checking for them, and by using the restriction they don't need to look, can have devastating results for a computer system. Back when I was learning to program in C, a programming language that gets you quite close to the metal, and under DOS it was very close to the metal, it was very easy to make a mistake with your pointers and end up overwriting bits of the operating system, randomly crashing the computer. This would be intermittant too, sometimes the program would run normally, other times the computer would just fall over dead. This is just the sort of thing that can happen when you try to open an image that has the wrong number of pixels in it. This can happen when the image file is just a simple image file. by allowing the use of files that have been written by some other device actually opens you up to a file that has been specifically altered to carry some specific data set that is designed to break things.


Even if you don't crash the camera you also have to consider that the limitation has the advantage of allowing optimised routines for things like image interpolation, for the different zoom levels. Simply knowing that you are only ever going to try to view images created by the camera greatly simplifies things from a computational perspective. For a start you don't have to do any checking to see if the data is even the right size before you begin.

If you were to allow the viewing of images from other devices you would need to implement a complete file browser system, as well as custom image viewing software, along with all it's support routines, that will now have to do a lot more work to get the image on screen. It will also, with out doubt, be a LOT slower in operation. IIRC ML have done a file browser, but I don't think that they have bothered with a universal image viewing program. I don't really see it being much of a priority for the programmers either. Not touching stuff that wasn't written to the card by the camera is actually quite a good idea.

Alan

So, let's get down to basics:

1) My normal procedure would be to "Import" files using eiher Lightroom or the Photoshop/Bridge Import function, and in doing so I would copy and move and rename the files according to my personal preferences as to image organizaation. So, the question is: I haven't tested this out yet, but if I do that, des that mean that if I copy my imported files/photos onto my memory card and insert it back into my camera, will those files/photos disappear? I haen't tried it ye, but that would be the test!!!!

BigAl007 wrote in post #18264704
If you were to allow the viewing of images from other devices you would need to implement a complete file browser system, as well as custom image viewing software, along with all it's support routines, that will now have to do a lot more work to get the image on screen. It will also, with out doubt, be a LOT slower in operation.

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But I can take a card out of one Canon DSLR and put it into another model of Canon DSLR and view the images without any problems. Back when I used a 5Dc and a 50D, I would routinely take the card out of the 5Dc and put it into the 50D to examine the files, because the 50D LCD screen was so much better than the 5Dc LCD screen. I mean, I did this on an every day, every hour basis. It was the only way I could "chimp" during a shoot to check my 5Dc images for critical sharpness and colour cast, because the 5Dc LCD is so horrible.

This complete interchangeability also works with the 1D2 and the 40D. Any of these 4 bodies could play back images shot with any one of the other 3 bodies.

I would also take half-full cards out of one body and then put them into another body and shoot photos, back when I had small cards and was always juggling them in order to have room for more pictures. When I finally got home after a lenghty photo trip, I would sometimes download CF cards that had images from 3 different cameras on them! Never had any problems with compatibility whatsoever. Heck, the buffers wouldn't even fill up noticeably slower, and the frame rate on burst mode wasn't noticeably slower, either.

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Files will be on the card and viewable on PC, but invisible to the camera.

oharing wrote in post #18264040
I have removed card/RAW photos from Canon DSLR, renamed photos and without changing them moved back to card and inserted camera.

Renaming is the problem. Canon only recognises IMG_xxxx.JPG and its raw format _MG_xxxx.CR2. It will show those on the screen if you copy them to a photo folder on the card.
My 60D "cannot play back image" if it's not native resolution, 5184×3456, so I resized the canvas of a smaller image made in Paintshop Pro to 5184×3456, renamed it to IMG_9150.JPG, copied it to the camera folder and the camera displayed it.
Remember that Canon will start numbering images from the highest IMG_xxxx number in the folder, or something like that.

Edit: Canon will start numbering images from xxxx, not start REnumbering.

JWdlft wrote in post #18265168
Renaming is the problem. Canon only recognises IMG_xxxx.JPG and its raw format _MG_xxxx.CR2. It will show those on the screen if you copy them to a photo folder on the card.
My 60D "cannot play back image" if it's not native resolution, 5184×3456, so I resized the canvas of a smaller image made in Paintshop Pro to 5184×3456, renamed it to IMG_9150.JPG, copied it to the camera folder and the camera displayed it.
Remember that Canon will start numbering images from the highest IMG_xxxx number in the folder, or something like that.

Edit: Canon will start numbering images from xxxx, not start REnumbering.

Interesting, that behavior is different from my own experiences. Canon changed something somewhere along the line to more current cameras.