Yup.
Different app, same engine underneath (QuickTime).
Jerry
On Mar 28, 2005, at 4:18 PM, Green, Cathy wrote:
> I've noticed a loss in quality when I import digital photos from my
> camera and view/save in Preview.? The files are smaller than the
> original, and there is a slight, albeit visually noticable, loss in
> quality.? Is this part of the same issue?? CCG
>
> ----------
> From: ? owner-macgroup at erdos.math.louisville.edu on behalf of Jerry
> Yeager
> Reply To: ????? macgroup at erdos.math.louisville.edu
> Sent: ? Monday, March 28, 2005 4:06 PM
> To: ??? macgroup at erdos.math.louisville.edu
> Subject: ?????? Re: MacGroup: lossless JPEG??? [bcc][faked-from]
>
> There has been a lot of talk lately about improvements in the jpeg
> compression ideas being used (Allume -- makers of StuffIt -- has some
> new stuff out that is supposed to shrink jpeg files up to 30% without
> any loss of quality) and a lot of speculation about how Apple is
> somehow reading the scheme used to compress the original imported jpeg,
> then using the exact same scheme to compress the newly saved image
> (this is supposed to maintain quality longer, through more levels of
> edits --- how Apple does this is also supposed to be a closely guarded
> secret -- at least according to the tin-hat-wearing folks, a bit
> doubtful since if Apple can get this info out of an arbitrary jpeg
> image, so can anyone else.)
>
> Not being a big iPhoto user (Go GIMP! Go PhotoShop!), I have only
> followed those discussions out of idle curiosity.
>
> But in terms of how iPhoto does do some of its wonders, you need to be
> careful here. Apple cheats. (Reeeeaaalllllyyyy big toothy grin!!!!!)
> If you import a jpeg photo, make changes, quit, come back make changes,
> quit et.c etc. the saved photo looks really good. Okay so far. But
> there is a menu option that says "Revert to Original". Choosing this
> takes you all the way back to the original imported image. So what
> Apple is doing is keeping a history of your editing for the photo and
> applying that to the original and showing you that. (Also if you take a
> gander through the iPhoto library you will see lots of data files
> popping up for your albums, especially after you start editing).
>
> On the other hand, if you edit a photo, then Export that, then import
> it back in, make changes, export it and import it again, etc. then you
> will begin to see image quality degradation within a few generations
> (using the jpeg format) that do not show up for the same edits on the
> one that stays inside of iPhoto the whole time.
>
> One thing that is creeping into the lexicon is the idea of what
> "lossless" means. With these new attempts to make jpeg last longer
> (instead of switching to the better jpeg2000 -- for jpeg compression)
> there is a lot of talk of thing being lossless in image quality, but
> not being a bit-for-bit identical copy. Hmm, it does sound like the
> words are going to be altered here soon.
>
> Shoot RAW NEFs, it's just better (smile).
>
> ??????? ??????? ??????? Jerry
>
>
>
>
> On Mar 28, 2005, at 11:00 AM, John Robinson wrote:
>
> > Lee,
> >
> > Thanks, as usual for a great explanation, but just for your info. my
> > eyes glaze over on most anything you say as you speak so far above my
> > capabilities, but boy do I ever learn from you!!
> >
> > John R.
> >
> >
> >
> >
> > On Mar 28, 2005, at 10:54 AM, Lee Larson wrote:
> >
> >> On Mar 27, 2005, at 9:22 PM, Bill King puzzled:
> >>
> >>> I just read an interesting article posted on MacSurfer from the
> >>> Syracuse Post-Standard newspaper.? It concerned the ability of
> >>> iPhoto 5 to repetitively save a picture using JPG compression and
> >>> apparently losslessly.
> >>>
> >>> I would love to hear for any graphics compression experts about the
> >>> authenticity of this technique...
> >>
> >> I'm not a graphics expert, but I think I can explain what's going
> on.
> >>
> >> The JPEG scheme is actually a whole collection of different
> >> compression techniques all lumped into one standard. The most
> common
> >> one chosen is what's called "discrete cosine transform" (DCT)
> >> compression. Within the DCT algorithm, you can choose the amount of
> >> information to be retained. (It's just the value of a constant in
> the
> >> formula.) The more information that's retained, the larger is the
> >> size of the compressed file. It's possible to choose lossless DCT
> >> compression, at the expense of almost no compression for complicated
> >> images.
> >>
> >> You can see this in programs like Canvas, which has a slider control
> >> to select the quality of the output image. Sliding it over to 100%
> >> results in a big file with no quality loss.
> >>
> >> The JPEG scheme also includes a lossless algorithm called entropy
> >> encoding which I believe is less often used than the DCT.
> >>
> >> I don't know which scheme Apple uses, but It's probably one of those
> >> two.
> >>
> >> As a postscript to this, let me note that I've had disagreements
> with
> >> so-called experts about this. They claimed that JPEG is an
> inherently
> >> lossy format while I countered that it need not be. Most "experts"
> >> don't really understand the capabilities of JPEG because most
> >> programs don't take advantage of JPEG's real capabilities. I bring
> up
> >> the DCT and their eyes glaze over.
> >
> >
> >
> > | The next meeting of the Louisville Computer Society will
> > | be March 22. The LCS Web page is <http://www.kymac.org>.
> > | List posting address: <mailto:macgroup at erdos.math.louisville.edu>
> > | List Web page: <http://erdos.math.louisville.edu/macgroup>
> >
> >
> -----------------------------------
> Someday, I will come up with a clever signature line. I am not sure if
> I will use it or not, but I will come up with one.
>
>
>
>
> | The next meeting of the Louisville Computer Society will
> | be March 22. The LCS Web page is <http://www.kymac.org>.
> | List posting address: <mailto:macgroup at erdos.math.louisville.edu>
> | List Web page: <http://erdos.math.louisville.edu/macgroup>
>
>
>
-----------------------------------
Someday, I will come up with a clever signature line. I am not sure if
I will use it or not, but I will come up with one.
| The next meeting of the Louisville Computer Society will
| be March 22. The LCS Web page is <http://www.kymac.org>.
| List posting address: <mailto:macgroup at erdos.math.louisville.edu>
| List Web page: <http://erdos.math.louisville.edu/macgroup>
