Re: JPG or TIFF


Scott W wrote:
Ron Hunter wrote:
> No, you don't HAVE to do a lot of compression, but then even at
minimal
compression, JPG formatted images have much of the original information
discarded, while TIFF retains all of it.

At true minimal compression a JPEG image has almost all of the original
image data encoded accurately to within +- 2 lsb. And much of the
reconstructed image data is exact. The exact statistics depend on the
target image. This is easy enough to test. A handful of modern cameras
do use absolutely minimal JPEG compression. Pentax IstD series for
instance.

But several brands of camera have "minimal" levels of JPEG compression
that are unacceptably brutal - founded in an era when flash memory was
expensive and stuck in a time warp. JPEGDUMP will sort the sheep from
the goats.

In cases where a limited
number of pixels is available to cover a larger space, this loss becomes
more significant. You can't get back what was discarded, and the more
information you retain, the better the end result.

The more *information* you retain the better. But obsessing about
storing all the noise as well is a just waste of space. JPEG by
construction cunningly manages to discard high frequency noise
preferrentially whilst retaining most of the important image
information content. Your image would be more different had you delayed
pressing the shutter by 1 millisecond than it is due to the JPEG losses
incurred at maximum quality.

The only posisble exception is in shadow detail of wildly underexposed
or extreme dynamic range images where 12bit TIFF comes into its own.

This issue comes up over and over again and seems to always be argued
on theory more then facts. Can you post a small crop of a tiff that
when saved as a jpeg at the highest quality setting from Photoshop
shows any visible difference to the tiff image?

I can, but the differences are pretty marginal. Contrast stretching and
zoom is needed to make them obvious. And apart from on very carefully
chosen awkward line art test pieces it is not a real problem. An 8x8
pixel example is all that is needed.

http://www.nezumi.demon.co.uk/photo/jpeg/2/jpeg2.htm

Note that the differences are only visible because the original
contained a pure flat noise free background and very sharp colour edge
transitions. Any real photographic image would usually contain enough
noise to disguise the quantisation error.

And Photoshop level 10/12 is still *not* the highest quality of JPEG
encoding possible. I chose it as representative of what was actually
available to end users.

JPEG is perfectly adequate for most practical purposes. It is important
to know when you do need to use TIFF and avoid believing in or
repeating bogus superstitions about JPEG.

Regards,
Martin Brown

.

Relevant Pages

  • Re: OT: Early Fall
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    (rec.boats)
  • Re: Is Tiff format lossless, no matter what Program you use?
    ... PhotoFiltre: No options whatsoever. ... "Save as...", select TIFF, set compression to JPEG. ...
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  • Re: JPEG compression in a TIFF file, pointless?
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  • Re: TIFF OR JPEG
    ... I am still shocked by the quality losses with even the gentlest JPEG ... You can save a lot of space by applying lossless compression to ... I just popped an image out of my camera and tried photoshop's TIFF ...
    (rec.photo.digital)
  • Re: 4mp doubled = 16mp!?
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