TIFF vs JPEG

[Marcus1234]

Again a newbie question.

I have a Canon Ixus 400. When I choose "superfin" and highest resolution I notice that I can shoot appr 125 photos with my 256 MB compact flash card. When I transfer the photos into the computer however I can choose between TIFF and JPEG file. If I choose JPEG the file turns out to be appr 2 MB but when I choose TIFF it turns out 11 MB. How on earth can that happen? It seems to be that my memory card saves 2 MB and the computer "blows it up" to 11 MB? Anyone who can explain this?

Regards

Marcus

[walwyn]

JPG can give far higher compression than TIFF but it does so at a price. That price is loss of information which is why the jpg format is termed 'lossy'.

What this means is that when you decompress a jpg file to view it the information you get back is not quite the same as the information you originally had. For photographs this doesn't matter as you wont generally be unable to determine where the differences are, which is why JPG is used in preference to other formats.

[Marcus1234]

But what I don´t understand is how is it possible for a file which is saved as 2MB on the memory card all of a sudden become 11 MB as a TIFF file? I would understand it if I only could shoot, say 23 TIFF-shots with a 256MB memory card but that isn´t the case, I can shoot 125 shots...every shot can turn out 11MB = 1.4GB with a 256 MB card???

[walwyn]

The reason is that the image is stored within the camera in a compressed format, probably JPG. It could output the image in "Dodah" format and it wouldn't affect how it was stored internally.

If you read your JPG picture into 'paint' and save it out as a "24 bit bitmap" bmp image you'll get a true indication of the images real data requirements.

[walwyn]

BTW: Your camera has 2,272 x 1,704 pixels (3,871,488 total) at 24 bit colour resolution you have to multiple by 3, which gives 11,614,464 bytes of uncompressed data.

[Marcus1234]

Thanks for the reply. Does this imply that it doesn´t matter if I save my photos in TIFF or JEPG regarding the quality of the pictures, i e in what format woud you advice me to save my original pictures?

Marcus

[walwyn]

Without knowing exactly how cannon compress there data I can't give a definative answer. However, I suspect there won't be much visible difference in any case.

Try it though - print the same picture saved in TIFF and JPEG and see if you can notice any difference. I have seen differences in the past but that was with specially prepared test images, and you had to be directed to the area of difference.

[Marcus1234]

I am still confused...

If my camera saves a photo as a JPG with 2 MB how is the camera then able to make it a TIFF-file with 11 MB? I maybe a beginner of this but my mind just doesn´t rest. If a file is compressed as JPG then it must be impossible to make it a TIFF?

Regards
Marcus

[normjackson]

Another slant.

Your camera takes the picture and compresses it to a 2MB jpeg to save space on your card and enable the save to happen quickly.

As Walwyn says, in doing this compression you will have lost some information as against what you would have had without this compression; but hopefully not a lot.

Converting the jpeg to a tiff will not get that lost information back. The only immediately obvious reason for converting the jpeg to tiff or one of the other "lossless" formats is if you want to do some processing on it, save it out and then maybe do some more processing.

You wouldn't want to keep changing your photo and then saving it as a jpeg each time since converting it to jpeg loses a little more information each time (in practice the accumulated loss may not be much of an issue at if you have used a high quality jpeg compression ie. one which compresses less but keeps more of the original info).

[Lawrie Hodges]

I don't know the spec of your particular camera so I too can only guess. You might check that that it doesn't have a TIFF storage mode. My Nikon 995 does, although I rarely use it. Certainly some Canon cameras have it and it may be that your transfer software is general purpose and is designed for number of slightly different models or perhaps since some older software requires TIFF format as import and maybe that is why your software makes the conversion from JPEG to TIFF as an option. As others have said, I would suggest that you transfer as JPEG, but that any further image processing done on the computer should be stored in a lossless form.

[walwyn]

To display your image it needs to convert it into pixels that can be displayed on the screen. Until it has to be displayed it can be compressed this is what the JPG format does, you can't display a JPG file without it being uncompressed back into pixels.

Think of it like an inflatable raft. You squash the air out to store it (JPG) and pump air into it to display it (PIXELS).

The uncompressed pixels can potentially be encoded into any format you like JPG, TIFF, PNG, BMP, GIF, THA, and about 1000 other formats.

Each format arose for historical reasons and have certain advantages over others for certain applications.

Here is a link to the rational behind TIFF:
http://home.earthlink.net/~ritter/tiff/

[normjackson]

I was thinking it's a pity you can't "lock" a thread like this. It's a disincentive to try and compose a carefully worded and comprehensive reply when the chances are that by the time you come to post it, someone has already done it and better than you could have!

I think Lawrie is probably right about the general purpose software. I don't think the S400 has the option to save as tiff.