working with tif. images?

[jim1971]

have a ? on this..when i scan my image that i plan to work i should save the file as a .tif opposed to a .jpeg? what is the reason for this? is it a cleaner image to work from? thanks

[MBChamberlain]

Jpeg compression is classified as a "lossy compression." Meaning that the compression method approximates the look of the image while removing as much data as possible. These methods create "artifacts" or marks on the image that are hard to edit around. The higher the compression ratio, the more artifacts will exist.

Tif is either uncompressed or lossless compression. Uncompressed is pure image data, while lossless compression finds patterns in the data and notates them with a code so it can remove one copy of a pattern and restore it later.

If you choose to use the jpeg compression set it as low as possible. (quality value is as high as it goes.)

Michael

[jim1971]

thanks MB
i think i understand what your saying.
i have another ? on this, just trying to figure out how to word it so i dont sound like a complete moron..lol
thanks again

[MaryLynn]

If someone had explained this to me a couple of years ago when I first started playing with "retouching", I wouldn't have ruined a picture that turned out to be the only one of my great grandfather. Let me tell you folks, it was not a pretty sight. Needless to say, each time I saved it as a jpeg, it got worse!

I learned to think of jpeg compression as somewhat like a marshmallow. If you squash a marshmallow it is still white, round and sweet. However, you can't restore the fluffiness that defines it as a marshmallow.

And the only moronic question you will ever have is the one you should have asked and didn't! Sometimes what seems like a simple question provokes the rest of us to think.

BTW, welcome to RP.
MaryLynn

[akj]

Thanks for the info Michael. So how does TIFF differ from RAW? I always have been meaning to ask, and this thread reminded me of it.

[jim1971]

well you kinda answerd my question i had in mind Marylynn.
what i was wondering was, if retouching a photo that was saved as a .tif gonna be better in the end then working from one that was saved as a .jpeg,

also is the print going to look much better?

[jim1971]

one more thing i thought of..
if i have a photo that is saved as a jpeg can i just resave it as a tiff or would i be better off rescanning the image again and then saving it as a .tif.
seems like i should rescan to play it safe..right?

[Kraellin]

here's a thread that may help you out: http://www.retouchpro.com/forums/history-conservation-repair/4906-file-format-use.html

i learned a few things in there as well.

K.

[jim1971]

great link Kraellin,,thanks
answered everything i needed to know or had questions on

[JayNads]

Originally Posted by akj

Thanks for the info Michael. So how does TIFF differ from RAW? I always have been meaning to ask, and this thread reminded me of it.

When you save a TIFF file, for example a 5 MB image, you have a 15MB saved file. Why? Because TIFF saves the file as 5MB Red, 5 MB Green, 5 MB Blue (3 layers of 1 color each). It's huge, but saves each pixel as data. RAW only works as a taken picture, not a working format, because it saves the same image as a (roughly) 5 MB file because . . . on your CCD, you have a repeating grid of two alternating strips of pixels. One is red and green, the next is blue and green. When your camera saves a RAW file, it saves the exact pixel data as the camera took (one layer of 3 colors, just like the CCD), rather than interpolating the missing pixels as JPEG and TIFF do (missing because the camera looks at the blue and green pixels to extrapolate the gaps between the red pixels, and so on for blue and green).

When you save it as a JPEG, the reason the file degrades over multiple saves is the way JPEG works. It examines an 6X6 block of pixels (might be 8X8, I forget), and determines the average pixel in the group. It then tries to bring the other pixels closer to that average because rather than saving the pixel data, it only saves the relative difference between those pixels and the average. By slightly altering the other pixels to reduce their difference, it shrinks the file. When you open it and re-save, it compresses again, yet again reducing the difference. This is why JPEG artifacts are most noticeable in high contrast places, because they are being averaged into squares, making the colors seem to bleed in geometric shapes.

I hope this was useful.

[byRo]

Originally Posted by JayNads

When you save it as a JPEG, the reason the file degrades over multiple saves is the way JPEG works. It examines an 6X6 block of pixels (might be 8X8, I forget).

It is in fact 8x8 for the luminosity information, and 16x16 for the colours.
If you want a bit more information have a look at this tutorial.

Rô

[jim1971]

Jaynads..thanks for the indepth explanation,found it very knowledgeable and you explained it a way that was easy to unterstand