[K-9]

How big a size do you have to go to really know you're getting a better print from a Tiff file? If you're printing 8x10 or under is it even worth saving RAW files as Tiff's to bring to the lab?

[dylansalt]

Too be quite honest for basic no pro lab processing up to A4 or even printing from my own printer I can't tell the difference one from the other bearing in mind that I print my A4's myself and will just use my tiff (pp'd from raw) file.

Also I think most labs kiosks will only accept jpeg format.

Dylan

[wlachan]

Good quality jpeg will do imho, tiff just slows down the printing process.

[ytterbium]

In JPEG colors have half the linear resolution (In 640x480 image you have 320x240 color image), but you wont see it, because human eye has much lower resolution for colours aswell - unless your viewing it much closer or it's a big print.

Then some artifacts may appear just because of jpeg, where you can observe colour information streching over the original "subject" - like a star for example, which is 1 pixel big will have a 2x2 pixel colour block.
So if some part of image consist mostly of contrasty colour information they migh get messed up. See samples, brightness (black/white) is intact but colors get damaged, even with 100% quality jpeg. (Note that 100% jpeg dosnt get even actual lossy compression, it gets only reduced colour resolution and basic losless compresson).
Attached are original bitmap file, 100% quality JPEG, upscaled BMP and upscaled jpeg, so can you tell the difference? I can, but i doubt i could without knowing and in a real image where you dont see clear RGB lines. Sometimes i only see this in astrophotographs.

Edit: i forgot to mention that JPEG isnt simply 8 bit - 255 shades of gray. It is true for gray - lightness but not for colour information. It processes images as YCbCr where Y - lightness usually gets its 255 levels but colour, depending on compression level may get anything below, like 2, 16, 64. Which might offset captured colour value or cause visible steps/noise in colour only gradients(Red->Blue,Green->Yellow etc, not Black-White, Dark->Light).

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Last edited by ytterbium; 08-01-2009 at 05:23 AM.

[procyon]

In JPEG colors have half the linear resolution

Just a small correction: that's correct for JPEG-s with 4:2:0 chroma subsampling, most decent editors switch to 4:2:2 (half colour resolution in one direction only) or 4:4:4 (full colour resolution) either automatically at higher quality settings (photoshop iirc) or let the user choose it.
But yes, even 4:4:4 JPEG-s at 100% quality still are not lossless and can cause artifacts in contrasty/sharp/saturated etc. places. Especially if someone decides to sharpen it or apply some other processing (curves, colour profiles etc.) to the JPEG file (lab technician ? ).

BTW I'm sure 99.999% of the time the JPEG is OK, but since the OP bothered with RAW anyway ....

If saved correctly there really is no difference. You just don't want to keep opening a jpeg, edit then save again. This is where loss occurs. Open your RAW, save as atiff if you've done anything to the image or may want to go back and mess with it later but save as copy to a jpeg for output.

[davemdsn]

I only print from RAW or PSD/TIFF if I am printing directly from my photo apps (Aperture or Photoshop) to my home printer. If they are being sent out to a lab it is always jpeg. As long as you don't do any editing after the image has been saved as a jpeg you won't see any difference in a print.

[K-9]

Thanks for the info. Does editing a Tiff lose quality? I know if you tweak a RAW file and then save it as a Tiff and then realize you want to do one more thing, you would have to either tweak the Tiff or start all over again in the RAW file.

Also, does rotating a jpg lose quality? I know rotating it in the camera doesn't, just for viewing, but how about if you rotate it in iphoto and then save it?

[davemdsn]

A tiff is a bitmap, which keeps every single pixel, so there is no loss of image quality beyond whatever edits you made. Same is true of PSD files, they are made to be saved over and over without pixel or color compression.

There may be quality loss in rotating a jpeg if for no other reason than you have re-saved the image. However, a single re-save will not result in a loss worth worrying about. If you jpeg save quality settings are set to high then you can do a couple saves with minimal loss. It's when you do it repeatedly that things get ugly.

A good rule of thumb is to treat ALL of your originals as negatives and never overwrite them. RAW file editors automatically never overwrite the image data in the file, but you want to make sure that they treat jpegs the same way. Always edit a copy, never the original.

For what it's worth, iPhoto never overwrites the original. The version you see after making any changes is a copy. You can always revert back to the original.

[Marc Sabatella]

Whether or not rotating a JPEG causes a quality loss (from de-compressing and then re-compressing the image) depends on your software and which of its methods you choose to rotate your image. If the software supports rotation by simply setting the EXIF Orientation field (which is how th camera does it), there is no loss. There are also algorithms for rotating the data itself losslessly, but not all pplications use these. You'd have to look into the document and/or support for your particular application to know.

But in any case, the degradation inherent in JPEG's lossy compression tends to be overstated. Most people would never notice unless you continually open the file and re-saved it, or if you choose a very low quality setting. A couple of re-saves at high quality and most people couldn't tell the difference, unless perhaps examing on screen at 100% or larger.

[K-9]

I have noticed that doing exposure or other color/brightness tweaks to a jpg causes noticeable sharpness loss right on screen after saving, however small things like rotating or slight cropping aren't as apparent. I suppose what you edit is a factor in how much the jpg degrades.

Where does the original get saved in Iphoto, as when I edit it, the new one seems to replace the old one? Oh, wait, nevermind. I just thought of the answer myself. I know there is an option if you click on an edited pick of reverting it back to the original. So, I guess it is somewhere, but just hiding.