Saving JPEG as TIFF

[Abitconfused]

Does saving a JPEG, fresh from the camera, as a TIFF file preserve detail?

[DanK]

JPEG discards information (it's "lossy"), while a TIFF is lossless. However, if you have shot in jpeg format, that means the camera has already converted it to jpeg, and the information is gone. Saving as a TIFF after that simply means that you won't lose any more. It won't regain what you have thrown out.

[Tronhard]

I gather you are starting off with a .JPG file. EAs I understand it, each time a JPG file is saved certain algorithms impact the file potentially causing a degradation. Saving it as a TIFF for and during PP file might preserve details that would otherwise be lost but it could not undo the work done by the camera in creating the original .JPG file, as opposed to originally creating a RAW file to begin with.

[rpcrowe]

Gosh... RAW is so easy to work with that I really don't know why (except for news and sports that demands immediate transmission) most folks do not shoot in RAW. I find it so easy to work with Adobe Camera RAW that I will, whenever possible. open JPEG images in camera RAW.

[xpatUSA]

Does saving a JPEG, fresh from the camera, as a TIFF file preserve detail?

Taking "preserve detail" literally, yes, saving as a TIFF preserves the detail that was in the JPEG file.

How much detail was in that JPEG file depends completely on how it was saved:

a) how much compression

b) type of sub-sampling

c) Photometric interpretation

d) Embedded color profile.

The absolute best (no loss of 'detail') will be:

a) no compression

b) no sub-sampling

c) RGB photometric interpretation

d) ProPhoto color profile

Hope this helps more than it confuses, Ed.

[Abitconfused]

Where does "sub-sampling" take place and what is it? Thank you.

[xpatUSA]

Where does "sub-sampling" take place and what is it? Thank you.

https://en.wikipedia.org/wiki/Chroma_subsampling

For imagery, it started with color television. The camera captured RGB but the transmission converted those three channels to two channels of color (chroma) and one channel of brightness (luma). This is no different to CIE's representation of a color by two numbers x,y with luminance Y being separate.

Sub-sampling can be used for JPEG images or not as is shown in the above link. Often, selection of JPEG quality 9 or more disables sub-sampling. In the EXIF it will say: Y'CbCr 4:4:4 (1:1).

The common types of sub-sampling found in JPEGS are:

4:4:4, none.
4:2:2, sub-sampled horizontally.
4:2:0, sub-sampled both horizontally and vertically.

You can find the type of sub-sampling used in the EXIF data.

4:2:0 is no different in principle from down-sizing an image by 50% except that the brightness is left at full-size - bit of a brain hurter, that.

Sub-sampling is a separate subject to data compression and is much more simple.

[miatab]

I read everything you said, Ted, then the material in the link. What I got from it is: "The details of chroma subsampling implementation cause considerable confusion." I hope Ed is now completely satisfied.

[dje]

Interestingly, Photoshop (at least CS6) uses 4:2:0 for jpeg quality settings of 1-6 and then jumps to 4:4:4 for settings 7-12. It seems that 4:2:2 doesn't get a look in. I'm not sure why this might be so.

Almost all consumer video uses 4:2:0 with a little bit of high end stuff using 4:2:2.

Dave