TidBITS#751/18-Oct-04
=====================
Apple and Microsoft jostle for position in this week's jumbo
issue. Apple reported a record $106 million quarterly profit,
has sold 150 million songs through the iTunes Music Store, and
just opened six new mini retail Apple Stores. Microsoft is
now shipping Virtual PC 7 (with support for the G5) and has
a bug-fix update to Microsoft Office 2004. Also in this issue,
Charles Maurer zooms in on digital camera sensor technology,
Adam and Matt Neuburg share radio air time, and we welcome
Rogue Amoeba as a new TidBITS sponsor!
Topics:
MailBITS/18-Oct-04
Microsoft Office 2004 for Mac Service Pack 1 Squishes Bugs
Virtual PC 7 Finally Arrives in Microsoft Office
Sense & Sensors in Digital Photography
Hot Topics in TidBITS Talk/18-Oct-04
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MailBITS/18-Oct-04
------------------
**Rogue Amoeba Sponsoring TidBITS** -- We're pleased to welcome
our latest long-term sponsor, the audio utility company Rogue
Amoeba Software. They're probably best known for Audio Hijack,
which helps you record any audio from any application, and Audio
Hijack Pro, which adds support for more audio formats, can enhance
the incoming sound in a variety of ways, and much more. These
applications are fabulous for recording music from your old LPs
or for timeshifting live Internet radio shows; the first thing
I did to test Audio Hijack Pro was to start recording the new
radio episodes of Hitchhiker's Guide to the Galaxy from BBC Radio
so I could listen to them on my iPod during a long car trip. Rogue
Amoeba has also used their expertise in Macintosh audio to create
Nicecast (which enables you to create your own Internet radio
station) and Detour (which redirects audio from different programs
to different output devices). They've also created a couple of
free applications that help you quickly switch between different
audio input and output sources and play sound from any input
device. It's great to see a small company carving out a niche for
itself like this, particularly when they're a fun little company
with a great name and hilarious iconic mascot. If you're at all
interested in audio, whether it's for making your own beep sounds,
timeshifting Internet radio shows from any application, converting
your vinyl to MP3, or just making your Mac's audio inputs and
outputs do your bidding, you'd be well served by checking out
Rogue Amoeba's software. We're glad to count them among our
sponsors. [ACE]
<http://www.rogueamoeba.com/tb/>
<http://www.bbc.co.uk/radio4/hitchhikers/>
**Apple Reports $106 Million Fourth Quarter Profit** -- Apple
Computer surprised both analysts and markets last week by
announcing its strongest fourth quarter in nine years, with
a $106 million profit on a whopping $2.35 billion in revenue
for the company's final fiscal quarter of 2004. Moreover,
Apple shipped more than 2 million iPod music players during
the quarter, and the quarter represents a startling 37 percent
revenue increase compared to the same quarter last year. The
results include a $4 million restructuring charge. Gross margins
for the quarter stayed high at 27 percent, and international
sales represented 37 percent of revenue. Significantly, Apple's
retail store revenue was up 95 percent from the same quarter
last year.
<http://www.apple.com/pr/library/2004/oct/13results.html>
<http://www.apple.com/ipod/>
Despite a delay caused by shortages of G5 processors, Apple says
the new iMac G5 is off to a strong start; Apple shipped 836,000
Macs during the quarter, more than half of which were iBooks and
PowerBooks. The 2.02 million iPods Apple shipped represents a 500
percent increase over the same quarter a year ago; some 6 percent
of those iPods were manufactured by Hewlett-Packard as part of
the companies' production alliance. What's stunning is that Apple
moved over a third of _all_ iPods (5.7 million) ever sold in just
the last three months. Looking forward, the company expects its
next fiscal quarter (which includes the holiday buying season)
to be strong, with revenues between $2.8 and $2.9 billion. [GD]
**Apple Sells Its One Hundred and Fifty Millionth Song** -- Apple
continued to remind everyone it's the 400-pound gorilla of the
online music industry by announcing it has now sold over 150
million songs on its iTunes Music Service. What's more, just
in time for the holiday shopping season, iTunes gift cards will
now be available in Best Buy stores in addition to Target and
Apple's own retail stores. The announcement follows yesterday's
financial results where Apple noted it shipped more than 2 million
iPods during its fourth fiscal quarter. Apple says it's selling
more than 4 million songs a week, which puts it at a pace to sell
over 200 million songs per year.
<http://www.apple.com/pr/library/2004/oct/14itunes.html>
<http://www.apple.com/itunes/>
This announcement's timing on the heels of fourth quarter results
permits me to note Apple's "other music products" (anything but
iPods) brought in $98 million last quarter, which is roughly
a one-third increase over the same quarter a year ago. Combined
with revenue from iPods, that means right now roughly one quarter
of Apple's revenue has to do with music, not computers. [GD]
**Apple Opens Mini Retail Stores** -- Further refining the retail
experience of buying a Mac or iPod, Apple opened six new retail
stores that feature a "mini" layout compared to existing stores.
The smaller design puts products and information along the side
walls (which are made up of aluminum panels, like a real-world
Finder!), with the main floor space open. A single retail counter
doubles as a Genius Bar. Most intriguing is a new self-checkout
kiosk built into one wall, where customers can scan and purchase
products without employee assistance. The stores appear to be
geared toward more general users: the iPod is heavily represented,
as are portables and the iMac, but the eMac and Power Mac G5 don't
appear at all. Apple now operates 93 Apple Stores in the United
States and Japan. [JLC]
<http://www.apple.com/retail/>
<http://www.apple.com/pr/library/2004/oct/14retail.html>
**Take Control of Upgrading to Panther Now in Dutch** -- Our
untiring Dutch translation team has gone beyond translating
TidBITS each week to bring Dutch-speaking Macintosh users a
translation of Joe Kissell's "Take Control of Upgrading to
Panther." As with our other translations, it's $7.50, with
a third of the price going to the translators. Continuing our
policy of supporting our early adopters, Dutch speakers who
already purchased the English version of "Take Control of
Upgrading to Panther" are entitled to a free copy of the Dutch
translation. If your English copy of the ebook has a Check for
Updates button on the first page, click it to access the download
page for the translation. If your copy of the ebook is too old
to have a Check for Updates button, you may be able to download
a new copy from eSellerate if you still have your receipt, or you
may still have the free coupon code we sent to purchasers before
we implemented the Check for Updates mechanism. We'll be sending
a direct download link to readers in the Netherlands and Belgium
as well, but if all else fails, please use the form on our FAQ
page to ask Tonya for help. [ACE]
<http://www.tidbits.com/takecontrol/nl/panther/upgrading.html>
<http://www.tidbits.com/takecontrol/faq.html>
**TidBITS Night on The Mac Night Owl Live** -- It was a TidBITS
double-header on The Mac Night Owl Live radio show with Gene
Steinberg on 15-Oct-04, as both Contributing Editor Matt Neuburg
and I talked with Gene. Matt's topic was his two new Take Control
ebooks on what's new in Word 2004, whereas Gene and I spent quite
a while talking about Apple's $106 million fourth quarter profit
and what all those numbers really mean. (Kudos to Geoff Duncan,
Mark Anbinder, and Glenn Fleishman for their coverage of Apple's
quarterly report on our ExtraBITS page, allowing me to sound way
more prepared than I might have been otherwise!) You can listen
to The Mac Night Owl Live on the Internet from the show archive;
it's worth the visit.
<http://www.macradio.com/Friday/>
<http://www.tidbits.com/extrabits/>
Microsoft Office 2004 for Mac Service Pack 1 Squishes Bugs
----------------------------------------------------------
by Adam C. Engst <[EMAIL PROTECTED]>
A few weeks ago, the PR person at Edelman who works with
Microsoft's Macintosh Business Unit contacted me to let me
know that there would be an automatic update to the Microsoft
AutoUpdate utility, a new part of Office 2004. Trying to figure
out if this warranted coverage, I asked, "So you're telling me
that AutoUpdate is going to kick in automatically to update
itself to better kick in automatically?" The answer was yes,
and I decided it fit into the same news category as a tree
falling in an uninhabited forest.
But now you really do want that 927K update to Microsoft
AutoUpdate (which you can find and launch manually in your
Applications folder if you turned off the Microsoft AU Daemon
in your Startup Items list), because the utility now has some
real work to do in downloading and installing Microsoft's 22.8 MB
Service Pack 1 for Office 2004, which fixes numerous security and
stability issues in the Office suite of programs.
<http://www.microsoft.com/mac/autoupdate/description/AUOffice2004111EN.htm>
Most important from my perspective is that Microsoft stamped out
the maddening selection bug in Word 2004, by which selecting by
word would often also select the word preceding the selection.
This fix alone makes Service Pack 1 essential in my mind. Other
Word improvements include the proper functioning of AutoRecover
when FileVault is enabled (note that we do not recommend the use
of FileVault except in very specific situations), text correctly
changing to the font selected from the Font menu, and correct
detection of Swiss German proofing tools. For additional help with
Word 2004's new features, see our just-released "Take Control of
What's New in Word" ebooks.
<http://www.tidbits.com/takecontrol/word-1.html>
<http://www.tidbits.com/takecontrol/word-2.html>
In Service Pack 1, PowerPoint 2004 sees improved performance when
you play movies in a slide show, better compatibility with fonts,
and corrected dragging of objects when the ruler is turned on.
The only change to Excel is also shared by Word and PowerPoint:
improved security when you open a document containing macros.
<http://support.microsoft.com/?kbid=886633>
Entourage 2004 also picks up a number of fixes. The Entourage icon
no longer bounces in the Dock when a connection error occurs, sent
messages display the sent status in the Microsoft Outlook Info
Bar, modem usage has been improved, SMTP over SSL has been
improved, attaching photos from iPhoto now works better, the
Microsoft User Data folder can now live on a network volume,
Entourage no longer eats certain keyboard shortcuts for Adobe's
CS products, and connections both to normal POP servers and Domino
IMAP servers now work better. If you need assistance learning to
use Entourage 2004's new features, check out our "Take Control of
What's New in Entourage 2004" ebook.
<http://www.tidbits.com/takecontrol/entourage-2004.html>
Lastly, the Remote Desktop Connection client 1.0.3 is more stable
when you minimize the window and when you copy and paste data to
Macintosh applications. Other stability improvements should help
those using Mac OS X 10.3 or later, and those running on Macs
with PowerPC G5 processors.
Virtual PC 7 Finally Arrives in Microsoft Office
------------------------------------------------
by Mark H. Anbinder <[EMAIL PROTECTED]>
Microsoft has released a long-awaited update to Virtual PC,
the emulation software acquired from Connectix over a year
and a half ago. Virtual PC 7, which is available as a standalone
product or as part of Microsoft Office Professional, boasts
faster performance, better integration with the Mac's fast
graphics processors, easier printing from Windows to the Mac's
printer, and, perhaps most importantly, compatibility with the
Power Mac G5.
<http://db.tidbits.com/getbits.acgi?tbart=07087>
<http://www.microsoft.com/mac/products/virtualpc/virtualpc.aspx?pid=virtualpc>
That Virtual PC was incompatible with Apple's flagship Power Mac
G5 desktops gave a black eye to both Apple and Microsoft, so the
mere resolution of this problem makes Virtual PC 7 newsworthy.
The G5 was announced at Apple's Worldwide Developer Conference
in June 2003, and Microsoft released Virtual PC 6.1 in September
2003 (and rolled it into an Office Professional bundle) with the
known limitation that it wouldn't work on a G5.
<http://db.tidbits.com/getbits.acgi?tbart=07325>
Microsoft claims performance improvement of 10 to 30 percent for
Virtual PC 7, which will be a welcome boost for users on the lower
end of the system requirements curve. (Virtual PC requires a 700
MHz or faster PowerPC G3, G4, or G5 computer and at least 512 MB
of RAM.)
Available now in English editions are a $250 Virtual PC 7
with Windows XP Professional, and a $500 Microsoft Office 2004
Professional Edition, including Virtual PC. An upgrade edition
of Office Professional is available for $330. The company says
French, German, Japanese, and Swedish editions will be available
in the months ahead, as will Virtual PC versions featuring Windows
XP Home or Windows 2000 Professional, and standalone (without
an OS) and upgrade editions.
Sense & Sensors in Digital Photography
--------------------------------------
by Charles Maurer
In another incarnation I was a commercial photographer. At the
end of that life I sold all of my studio equipment and all of
my cameras save one, a Horseman 985, a contraption with a black
bellows that resembles the Speed Graphic press cameras you
see in pre-war movies. It uses roll film and allows the front
and back of the camera to be twisted in every direction when
it's parked on a tripod. You can also hold it in your hands
and pretend you're acting in "Front Page." Never have I found
a camera so useful. Nowadays, however, digital sensors are
pushing the optical limits of lenses and software has become
more pliable than leather bellows, not just for adjusting
colour but for optical manipulations as well. This year a
modestly priced (as such things go) digital SLR supplanted my
Horseman. I can no longer see owning a camera that uses film.
In this article I am going to examine the technology of digital
cameras, but in an unconventional way. I am going approach it
from basic principles. This approach may seem abstract and
theoretical at first, but it won't for long. You will see that
if you understand the scientific principles, you can ignore a
lot of marketing hype and save significant sums of money.
**Photocells** -- Imagine a small windowpane with bits of a
special metal embedded in the glass and a wire touching
those bits. Photons of light bang against the glass. The impact
unsettles electrons in the metal. They bang into electrons within
the wire, which bump into electrons further down the wire, which
bump into still more electrons, so that a wave of moving electrons
passes along the wire - an electrical current. The more photons
that bang into the pane, the more electricity flows.
This is a photocell, a sensor that is sensitive to the intensity
of light. Now imagine millions of cells like this assembled into
a checkerboard and shrunk to the size of a postage stamp. Put this
stamp-sized collection of photocells inside a camera where the
film usually goes. The lens projects an image onto it. Each cell
receives a tiny portion of the image and converts that portion
into an electrical charge proportionate to the amount of light
forming that portion of the picture. Now we have a photosensor.
The complete matrix of charges on this photosensor forms an
electrical equivalent of the complete image - but only of the
intensity of the image. Since the eye interprets the intensity
of light as brightness, brightness devoid of colour, this
photosensor provides the information of a colourless photograph,
of a black-and-white photograph. If we feed the output of the
photosensor to the input of a printer, and if we let the printer
spray ink on paper in inverse proportion to the voltage (lower
voltage, more ink), then we will see a black-and-white photograph
appear. The output of the photosensor can be connected directly
to the printer through an amplifier, or it can be converted
into digital numbers and the digital numbers can be sent to the
printer. The first approach is analog, the second is digital.
The greater the range of digital numbers, the finer the steps
from black to white. If there are enough steps, the printout
will look like a continuous-tone photograph.
To make a photosensor record colour, we need to make it sensitive
to wavelengths of light as the eye is sensitive to them. We see
long wavelengths weakly as reds, short wavelengths very weakly as
blues, and medium wavelengths strongly as greens. The easiest way
to make a black-and-white photosensor record colour is to put
filters over the cells so that alternate cells respond to short
wavelengths, medium ones and long ones. Since the eye is most
sensitive to medium wavelengths, it is practical to use twice
as many of these as the others: one blue, one red, two greens.
Such a set of filtered cells - red, green, blue, green - forms
the Bayer photosensor (named after its inventor) that is used
in nearly every digital camera.
Now consider what happens when a spot of light is smaller than
a group of four cells, when it is small enough to strike only a
single cell. Assume the spot to be white light, which includes
every wavelength. If the white spot falls on a blue-filtered cell,
then the picture will show the spot to be blue. If the white spot
falls on a red-filtered cell, the picture will show the spot
to be red. If it falls on a green-filtered cell, the spot will
look green. This can cause so many errors in the image that
manufacturers try to prevent it from happening by blurring the
image, by putting a diffusing filter in front of the sensor
to smear small spots of light over more than one cell.
Note that in a sensor like this, four cells form the smallest
unit that can capture full information about some part of a
picture. That is, four cells form the basic element of a picture,
the basic "picture element" or "pixel". Unfortunately, to make
their products sound more impressive, manufacturers count cells
as pixels. That's like saying a piano has 234 notes, not 88,
because it is built with 234 strings. Since the sensors function
differently at the level of the cell and the level of the pixel,
it is important to ignore the advertising and to discriminate
appropriately between pixel and cell. I shall do that in this
article.
A simpler approach would be to design a sensor in which every
cell is sensitive to every wavelength. Such a sensor was patented
by Foveon, Inc., in 2002, and is currently in its second
commercial generation. Foveon's sensor uses no coloured filters
but instead embeds photo-sensitive materials within the silicon
at three depths. The longer the wavelength of the light,
the farther it penetrates the semi-transparent silicon and the
deeper the photo-sensitive material it stimulates. With a Foveon
sensor, every cell records a complete pixel with all wavelengths.
(Note, however, that Foveon have taken to multiplying the number
of pixels by three, to sound competitive in their ads.)
**How many pixels do you need?** The smallest detail usable in a
print is defined by the finest lines that a person can see. At a
close reading distance (about 10 inches, or 25 cm), somebody with
perfect vision can resolve lines slightly finer than those on the
20/20 (6/6) line of the eye chart, lines of about 8 line-pairs per
millimetre (l-p/mm), which is the unit of optical resolution.
However, those are black-and-white lines. No ordinary photograph
contains black-and-white lines so thin because no camera can
produce them on photographic (as distinct from lithographic) film.
No lens can create such fine lines without beginning to blur the
blacks and whites into grey. Dark-grey-and-light-grey lines need
to be thicker than black-and-white lines to be seen. In the
perception of fine lines, a halving or a doubling of thickness
is usually the smallest difference of any practical significance,
so this pronouncement of Schneider-Kreuznach sounds perfectly
reasonable to me: "A picture can be regarded as impeccably sharp
if, when viewed from a distance of 25 cm, it has a resolution
of about 4 l-p/mm." On an 8" x 12" photo, this is 1,600 by 2,400
pixels, or 3.8 megapixels. (8" x 12" is about the size of A4
paper. It isn't quite a standard size of a photo but will prove
more convenient for discussion than 8" x 10".)
In short, 4 million pixels carry all of the useful information
that you can put into an 8" x 12" photograph. Finer detail
than this will matter to technical aficionados making magnified
comparisons, and it may matter for scientific or forensic tasks,
but it will not matter for ordinary purposes. The same holds for
larger prints because we don't normally view larger photographs
from only 10 inches away. It holds even for the gigantic images
in first-run movie theatres. The digital processing used routinely
for editing and special effects generates movies with no more than
2,048 pixels of information from left to right, no matter how wide
the screen. The vertical dimension differs among cinematic formats
but is typically around 1,500 pixels.
This, of course, presents quite a paradox: a frame of a
Cinemascope print obviously contains a lot more than 4 million
pixels. Even an 8" x 12" print from a 300-dpi printer contains
2,400 pixels by 3,600 pixels, or 8.6 million pixels. Large prints
need those additional pixels to prevent our seeing jagged edges
on diagonal lines, because the eye will see discontinuities in
lines that are finer than the lines themselves.
Since no photograph of any size can contain more than 3 to 4
million elements of information, even when made from film,
any substantial enlargement needs to be composed primarily
of pixels that do not exist in the original. These pixels need
to be interpolated: interpolated through continuous optical
integration (film), interpolated mechanically (high-resolution
scanner), or interpolated logically by software (digital
photography). This need for interpolation in enlargements
makes interpolating algorithms fundamentally important to
digital photography. For most enlargements, the quality of
the interpolating algorithm matters more than the resolution
of the sensor or the quality of the lens. We shall come back
to this.
For the moment - indeed, forevermore - it is essential to keep
straight the distinction between (1) the information that is
contained within an image and (2) the presentation of this
information. Both are often measured by pixels but they are
orthogonal dimensions. The information within a picture can be
described by a certain number of pixels. That information may
be interpolated into any number of additional pixels but doing
so adds nothing to the information, it merely presents the
information in smaller pieces.
To illustrate this, here are some examples:
* A good 8" x 12" photograph and the same photo run full-page in a
tabloid newspaper both contain about 1 megapixel of information.
* A slightly better photograph and the same photo run full-page
in a glossy magazine and a broadsheet newspaper all contain about
1.9 megapixels of information.
* A slightly better photograph still - the best possible - and the
same photo spread over two pages in a glossy magazine both contain
about 3.8 megapixels of information.
If you have an 8" x 10" photo printer, you can compare those
levels of information by printing out a set of pictures
(linked below, about 30 MB) that I took at approximately
those resolutions, keeping everything else the same. (The test
pictures were shot at 3.4, 1.5 and 0.86 megapixels: I used
a Foveon sensor and, to generate the lower resolutions, used
its built-in facility to average cells electronically in pairs
or in groups of four.) I enlarged the pictures using the best
interpolator I could find to 3,140 by 2,093 pixels.
<http://www.tidbits.com/resources/751/HighMedLowResolution.zip>
The photos are JPEG 2000 files, saved in GraphicConverter
at 100 percent quality using QuickTime lossless compression.
To prepare them I adjusted the levels, cleaned up some dirt in
the sky, then enlarged them in PhotoZoom Pro using the default
settings for "Photo - Regular." Those settings include a modest
and appropriate amount of sharpening.
What you will see, if you print them, is surprisingly small
differences from one level of resolution to the next. Each of
these photos looks sharp on its own, and at arm's length they all
look the same. You can see a difference only if you compare them
up close. That, of course, is because the only information that's
missing from the lower-resolution pictures is information that
is close to the limit of the eye's acuity and thus is difficult
to see.
**Bayer vs. Foveon in Theory** -- Cameras today fall into two
categories, those with a Bayer sensor and those with a Foveon
sensor, which at this writing include only two, a theoretical
Polaroid 530 and a very real Sigma SD-10.
<http://www.pdcameras.com/usa/catalog.php?itemname=x530>
<http://www.foveon.com/SD10_info.html>
In a Bayer sensor, a single cell records a single colour, but a
pixel in the print can be any colour. Carl Zeiss explain this:
"Each pixel of the CCD has exactly one filter color patch in front
of it. It can sense the intensity for this color only. But how can
the two remaining color intensities be sensed at the very location
of this pixel? They cannot. They have to be generated instead
through interpolation (averaging) by monitoring the signals from
the surrounding pixels which have filters of these other two
colors in front of them."
Since the cells provide a lot of partial information, the
interpolation can be accurate, but it can be inaccurate as well.
Patterns of coloured light can interact with the checkerboard
pattern of filters over the cells to generate grotesque moire
patterns. To avoid these, Bayer sensors are covered with a filter
that blurs every spot of light over more that one cell. The net
result proves to be interpolated resolution that varies with
colour and peaks with black-and-white at about 50 percent more
line-pairs/millimetre than the intrinsic resolution of the sensor.
This sounds like a lot but cannot be seen unless you look closely.
More problematic is the fact that this filter does not merely
prevent moire patterns, it also blurs edges. With a Bayer sensor,
every edge of every line is blurred. You can see the interpolated
resolution and the blurring in the magnified tests in the picture
linked below. There I have compared cameras with a Foveon and a
Bayer sensor containing the same number of pixels - pixels, not
cells. Both have 3.4 million pixels (although the Bayer has 13.8
million cells).
<http://www.tidbits.com/resources/751/Resolution.jpg>
People make a big deal about resolution because it sounds
important and is easy to test, but aside from special cases
like astronomical observation, fine resolution actually matters
little. By definition, at the limits of resolution, we can
only just make out detail. Anything that is barely visible will
not obtrude itself upon our attention or be badly missed if it
is not there. What we see easily is what matters to us, what
determines our impression of sharpness. Our impression of
sharpness is determined by the abruptness and contrast at the
edges of lines that are broad enough to be easily made out. You
can see this with the two tortoises in this picture linked below.
The sharper tortoise has less resolution but its edges are more
clearly defined.
<http://www.tidbits.com/resources/751/Sharpness.jpg>
The Bayer sensor resolves finer black-and-white lines but a Bayer
sensor will not reproduce any line so sharply as the Foveon. As a
result, when comparing two top-quality images, I would expect the
Bayer's image to look slightly more impressive when large blow-ups
are examined up close, but I would expect the Foveon's to look
slightly clearer when held a little farther away. Moreover, when
detail is too fine for the sensor to resolve, the Bayer looks ugly
or blank but the Foveon interpolates pseudo-detail. This means
that in some areas, large enlargements examined closely might
actually look better with the Foveon. In sum, I would expect
the 3.4 megapixel Foveon and what is marketed as a 13.8-megapixel
Bayer to be in the same league. I would expect photographs from
them to be different but comparable overall, if they are enlarged
with an appropriate algorithm.
**Bayer vs. Foveon in Practice** -- "If they are enlarged with
an appropriate algorithm..." - that statement is critical to a
sensible comparison. Usually, if you magnify an object a little,
it won't change its appearance much. If you simply interpolate
according to some kind of running average, you can increase its
size to a certain extent and it will still look reasonable. This
is how most enlargements are made. It is the basis of the bicubic
algorithm used in most photo editors, including Photoshop and,
apparently, Sigma's PhotoPro. It is also the basis of most
comparisons between Bayer and Foveon. However, a running average
will widen transitions at the edges of lines, and it will destroy
the Foveon's sharp edges, softening them into the edges of
a Bayer. A better class of algorithm will stop averaging at
lines. Any form of averaging, though, tends to distort small
regularities (wavelets) that occur in similar forms at different
scales. Best of all are algorithms that look for wavelets,
too. The only Macintosh application I know of in that class
is PhotoZoom Pro. PhotoZoom Pro has a limited set of features
and some annoying bugs - version 1.095 for the Mac feels like
a beta release - but it creates superb enlargements.
<http://www.trulyphotomagic.com/>
An appropriate comparison of the Bayer and Foveon sensors would
see how much information these sensors capture overall. (How much
spatial information, that is: comparing colour would be comparing
amoebas, as I explained in "Colour & Computers" in TidBITS-749_.)
To do this, I tested an SD-10 against an SLR that was based on a
larger Bayer sensor, a sensor 70 percent larger than the Foveon
that contained 13.8 million cells. Kodak were most helpful in
supplying this camera once they heard Doctors Without Borders
(Medecins sans Frontiers) was to benefit (see the PayBITS block
at the bottom of this article to make a donation if you've found
this article helpful). Also, Sigma sent me a matched pair of
50-mm macro lenses to use with the cameras.
<http://db.tidbits.com/getbits.acgi?tbart=07840>
I copied an oil painting with a wide variety of colours and a
lot of fine textural detail. With each camera I photographed
a large chunk of the painting, cropped out a small section from
the centre, blew up that section to the same size as the original
using PhotoZoom Pro (the defaults for "Photo - Regular"), and
compared that blow-up to a gold standard, a close-up that had
not seen any enlargement, interpolation, or blurring filter in
front of the sensor. Before blowing them up I balanced all three
photos to be as similar as I could, then, to prevent unavoidable
differences in colour from confounding the spatial information,
I converted all three images to black-and-white. I did this in
ImageJ. First I split each image into its three channels, then
I equalized the contrast of each channel across the histogram,
then I combined the channels back into a colour picture, converted
the new colour picture to 8-bit, and equalized the contrast of
the 8-bit file. (See the second link below for an explanation
of contrast-equalization.) I chose a painting in which most of
the coloured brush strokes were outlined with black brush strokes,
so that adjacent colours would not merge after conversion into
a similar shades of grey. With my 314-dpi printer, the two
enlargements are the equivalent of chunks from a 14" x 21".
<http://rsb.info.nih.gov/ij/>
<http://homepages.inf.ed.ac.uk/rbf/HIPR2/histeq.htm#1>
The difference between the photos from the Bayer and Foveon is
very slight. The two pictures are indistinguishable unless you
compare them closely. Fine, contrasty lines on the standard are
finer on the Bayer, more contrasty on the Foveon. The one that
looks more like the standard depends upon the distance from the
eye and the lighting but the differences are trivial. The two
images do contain slightly different information, but they
contain comparable amounts overall.
On the other hand, for efficiency of storage and speed of
processing, the Foveon wins hands down. This is how two identical
pictures compared:
> Foveon Bayer
> RAW 7.8 MB 14.7 MB
> 8-bit TIFF 9.8 MB 38.7 MB
If you would like to print out my test pictures, you can
download them. However, for the comparison to be meaningful,
you must specify a number of dots per inch for the pictures
that your printer can resolve in both directions. I know that
an Olympus P-440 can resolve 314 dpi, with no more than occasional
one-pixel errors in one colour's registration. I have not found
any resolution that an Epson 9600 can handle cleanly in both
directions, although I have not been able to test it exhaustively.
Other printers I know nothing about. You will have to experiment
with the test patterns in the Printer Sharpness Test file linked
below. For this purpose, only the black-and-white stripes matter.
<http://www.tidbits.com/resources/748/PrinterSharpnessTest.zip>
Each picture in the 5.8 MB file below is 1512 pixels by
approximately 2270. If a picture has been printed correctly,
the width in inches will be 1512 divided by the number of dots
per inch. Print them from Photoshop or GraphicConverter; Preview
will scale them to fit the paper.
<http://www.tidbits.com/resources/751/Bayer_vs_Foveon.zip>
Remember that the question to ask is not which picture looks
better or which picture shows more detail but which picture looks
more like the gold standard overall. I suggest that you compare
the pictures upside down. Remember, too, that these are small
sections from big enlargements that you would normally view
framed and hanging on a wall. Also, although the contrast is
equalized overall, the original colours were not quite identical
and the equalization of contrast amplified some tonal differences.
If you perceive the Bayer or Foveon to be better in one or another
area, make sure that in this area the tonality is similar. If
the tonality is different, the difference there is probably an
artifact. An example of this is the shadow beneath the tape on
the left side.
I have not been able to test this but I suspect that the most
important optical difference between Bayer and Foveon sensors
may be how clearly they reveal deficiencies in lenses. Since the
Foveon sensor is sharper, I would expect blur and colour fringing
to show up more clearly on a Foveon sensor than a Bayer.
**Megapixels, Meganonsense** -- Megapixels sell cameras as
horsepower sells cars and just as foolishly. To fit more cells
in a sensor, the cells need to be smaller. It is possible to
make cells smaller than a lens can resolve. Even if the lens can
resolve the detail more finely, doubling the number of cells makes
a difference that is only just noticeable in a direct comparison.
On the other hand, small pixels create problems. Electronic
sensors pick up random fluctuations in light that we cannot see.
These show up on enlargements like grain in film. Larger cells
smooth out the fluctuations better than smaller cells. Also,
larger cells can handle more light before they top out at their
maximum voltage, so they can operate farther above the residual
noise. For both reasons, images taken with larger cells are
cleaner. Enlargements from my pocket-sized Minolta Xt begin
to fall apart from too much noise, not from too few pixels.
In contrast, enlargements from my Sigma SD-10 have so little noise
that they can be enormous. A 30" x 44" test print looked as though
it came from my 2-1/4" x 3-1/4" Horseman. The Sigma has less
resolution than the Horseman - it's probably less than can be
extracted from scanning the finest 35-mm film - but its noise
level can be reduced to something approaching 4" x 5" sheet film.
Such a low level of noise leaves the detail that it contains,
which is substantial, very clean. In perception, above a low
threshold, the proportion of noise to signal matters far more to
the brain than the absolute amount of signal. Indeed, if I look
through a box of my old 11" x 14" enlargements, the only way I can
distinguish the 35-mm photos from the 2-1/4 x 3-1/4" is to examine
smooth tones for noise. I cannot tell them apart by looking at
areas with detail.
In sum, with the range of sensors used in cameras today, there
is no point to worrying about a few megapixels more or less.
Shrinking cells to fit more of them in the sensor can lose more
information than it gains. The size of the cells is likely to
be more important than their number. For the same money, I would
rather buy a larger sensor with fewer pixels than a smaller sensor
with more pixels. If nothing else, the larger sensor is likely
to be sharper because it will be less sensitive to movement of
the camera. For a realistic comparison of sensors as they are
marketed see this chart:
<http://www.tidbits.com/resources/751/SensorChart.png>
**Tripod vs. Lens** -- Most people believe that the quality of
the lens is of primary importance in digital photography.
If you have stayed with me so far, you may not be surprised
to hear me calculate otherwise. With 35mm cameras, an old rule
of thumb holds that the slowest shutter speed that a competent,
sober photographer can use without a tripod and still stand a good
chance of having the picture look sharp is 1 divided by the focal
length of the lens: 1/50" for a 50-mm lens, 1/100" for a 100-mm
lens, etc. At these settings there will always be some slight
blur but it will usually be too little to be noticed. This blur
will mask any difference in sharpness between lenses. To see
differences in sharpness requires speeds several times faster.
With digital cameras that use 35-mm-sized sensors, the same rule
of thumb holds, but most digital cameras use smaller sensors.
With smaller sensors, the same amount of movement will blur more
of the picture. If you work out the trigonometry, you'll find that
you need shutter speeds roughly twice as fast for 4/3" sensors and
four times faster for 2/3" and 1/1.8" sensors. (Digital sensors
come in sizes like 4/3", 2/3" and 1/1.8". Those numbers are
meaningless relics from the days of vacuum tubes; they are now
just arbitrary numbers equivalent to dress sizes.) That means
minimal speeds of 1/100" and 1/200" for a normal lens. Differences
in sharpness among lenses would not be apparent until shutter
speeds are several times higher again. Because of this, it strikes
me that the weight of lenses matters more to image quality than
the optics. The heavier a camera bag becomes, the more likely
the tripod will be left at home.
(Note that this does not mean that 35-mm-sized sensors are best.
Other optical problems increase with the size of the sensor.
As an overall compromise, the industry is beginning to adopt
a new standard, the 4/3", or four-thirds, which is approximately
one-half the diameter of 35-mm. This is not unreasonable.)
Frankly, I should be astonished to find any lens manufactured
today that does not have sufficient contrast and resolution
to produce an impressive image in the hands of a competent
photographer. I know that close comparisons of photos shot on
a tripod will show differences from one lens to another, and
I know that some lenses have weaknesses, but very few people
will decorate a living room with test pictures. In the real
world, nobody is likely to notice any optical deficiency unless
the problem is movement of the camera, bad focus, distortion or
colour fringing. It is certainly true that distortion and colour
fringing can be objectionable but, although enough money and
experimentation might find some lenses that evince less of these
problems than others, as a practical matter, especially with
zoom lenses, they seem to be inescapable. Fortunately, these
can usually be corrected or hidden by software.
Indeed, even a certain amount of blur can be removed with
software. Let's say that half of the light that ought to fall
on one pixel is spread over surrounding pixels. Knowing this,
it is possible to move that much light back to the central pixel
from the surrounding ones. That seems to be what Focus Magic does
(see the discussion of Focus Magic in "Editing Photographs for
the Perfectionist" in TidBITS-748_).
<http://www.focusmagic.com/>
<http://db.tidbits.com/getbits.acgi?tbart=07832>
**One More Myth** -- Finally, I would like to end this article
by debunking a common myth. I have often read that Bayer
sensors work well because half of their cells are green and
the wavelengths that induce green provide most of the information
used by the eye for visual acuity. This made no sense to me but
I am not an expert on the eye so I asked an expert - three experts
in fact, scientists known internationally for their work in visual
perception. I happened to be having dinner with them. It made no
sense to them, either, although I took care to ask them before
they had much wine. Later I pestered one of them about it so much
that eventually she got out of bed (this was my wife Daphne) and
threw an old textbook at me, Human Color Vision by Robert Boynton.
In it I found this explanation:
"To investigate 'color,'" an experimenter puts a filter in front
of a projector that is projecting an eye chart. "An observer,
who formerly could read the 20/20 line, now finds that he or she
can recognize only those letters corresponding to 20/60 acuity
or worse. What can be legitimately concluded from this experiment?
The answer is, nothing at all," because the filter reduced the
amount of light. "A control experiment is needed, where the same
reduction in luminance is achieved using a neutral filter....
When such controls are used, it is typically found that varying
spectral distribution has remarkably little effect upon visual
acuity."
In short, each cell in a Bayer sensor provides similar information
about resolution. It is true that green light will provide a Bayer
sensor with more information than red and blue light but that is
only because the sensor has more green cells.
If you want to shop for a digital camera, this article will help
you make the most important decision, what kind and size of sensor
to buy, with how many pixels. Once you have decided that, a host
of smaller decisions await you. My next article will walk you
through these. It is also going to incorporate a review of the
Sigma SD-10 and will appear shortly after one more lens arrives
from Japan.
PayBITS: If Charles's explanation of resolution and debunking of
the megapixel myth were useful, please support Doctors Without
Borders: <http://www.doctorswithoutborders-usa.org/donate/>
Read more about PayBITS: <http://www.tidbits.com/paybits/>
Hot Topics in TidBITS Talk/18-Oct-04
------------------------------------
by TidBITS Staff <[EMAIL PROTECTED]>
The second URL below each thread description points to the
discussion on our Web Crossing server, which will be much faster.
**Overwhelmed by TAO** -- Following Matt Neuburg's article about
TAO in TidBITS-750_, a couple of readers wonder whether the
outliner's interface hinders its utility. (3 messages)
<http://db.tidbits.com/getbits.acgi?tlkthrd=2340>
<http://emperor.tidbits.com/TidBITS/Talk/202>
**Home Theater Harmony** -- Andrew Laurence's review of
the Harmony Remote sparks discussion of all-in-one remote
control devices. (7 messages)
<http://db.tidbits.com/getbits.acgi?tlkthrd=2339>
<http://emperor.tidbits.com/TidBITS/Talk/201>
**Digital photo editing advice** -- Readers react to Charles
Maurer's articles on digitally correcting photos. (6 messages)
<http://db.tidbits.com/getbits.acgi?tlkthrd=2338>
<http://emperor.tidbits.com/TidBITS/Talk/200>
$$
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