> What MikeG is saying is that it does make a difference, blurring the
corners, in his experience.
That absolutely used to be the case. I've used Lightroom almost exclusively
for the past seven years and have found that this algorithm and the lens
profiles has gotten so good that the corner degradation is largely a thing
of the past. Not totally, but with these latest/greatest (or semi-greatest)
lenses from Sony, the results are excellent. That said, my 28-70 kit lens
totally sucks pond water. Well, it sucked ocean water...
> Digital rejiggering of images decreases sharpness. That's just the way it
is. MikeG can do the math; me, not so much.
> Ctein contends that Bayer array color loses about as much fine detail as
halving resolution, because of the interpolation.
So, interesting thing about that. I called Ctein out on it and he
acknowledged that it was based on one style of algorithm, but then defended
it by saying "well, the color information still has lower resolution."
It depends on which converter, and which version, and which camera sensor.
So nobody is right, and nobody is wrong.
Converters can use a 3-pixel merge or a 4-pixel merge. There is such a huge
misconception about the 2x green pixels and everybody thinks that it has
something magical to do with the luminance information used by the green
channel and so forth. Actually, the reason for the 2x green pixels is that
when we use the 'nearest neighbors of the "intersection" of the pixels,
there is always one green, one red, one blue pixel to work from. The
lumenance and color is derived from the averaging of those three pixels.
Not four. It's a rare converter that actually uses 2 green. One of the
problems with the Olympus E1 was that it NEEDED a 4-pixel merge in order to
keep from turning the picture into a mosiac. Converters used to treat
luminance separately from color, but they are now mostly done together and
is based on the three-pixel merge for both.
As to the 50% loss of resolution, I would disagree because the empirical
evidence shows that with the application of the appropriate sharpening at
the pixel level, we can achieve per pixel edge definition. The difference
between what Oly's HR mode and a standard merge is doing is that HR mode
does not require the corrective sharpening. That said, where HR mode really
shines is the increased depth of color and glassiness to the image which is
likely a result of the oversampling that is occuring.
Which brings me to the parallel. I'm deep deep deep into music production.
One of the things that completely transformed digital audio was
"oversampling." 30 some years ago I helped create one of the first
oversampling algorithms. (A different better one became the standard, oh
well). Anyway, the general ideal behind oversampling is to better represent
what is going on BETWEEN the samples. Without oversampling, it was the job
of the low-pass filter to eliminate all one-sample transients as well as to
prevent aliasing. This low-pass filter effectively reduced the TRANSIENT
frequency response of the audio signal by a minimum of 50%, and a more
typical maximum of 90%. In other words, a 44.1kHz song on a CD would have a
sine-wave frequency response of around 20Hz to 20kHz, but the transient
frequency response (square wave, saw wave), was 2kHz or lower. This not
only affected the type of sound being played back, but also the position of
the sound. Phase coherency was lost. Through oversampling and the
elimination of hardware-based low-pass filters, we are able to not only
maintain more phase coherency, but the position of the sound is maintained.
I'm oversimplifying to the point of inaccuracy, but you already know that's
what I tend to do.
I bring this up because with Lightroom's latest/greatest converter,
especially with the SONY cameras, it is actually performing a multi-pass
process which does the normal convert of the nearest neighbors, but then
does a second convert to calculate the in-between values. This is then
combined to find a better value for the resulting pixel. I haven't figured
out how much it is applying, but it's definitely throwing extra spices into
the pot of chili.
So, related content: Yesterday, I met Wayne and his lovely wife at their
home north of Melbourne. While no pixels were harmed, we had a terrific
lunch as we realized that this Olympus list friendship has gone on for
almost 30 years! I had to cut our time short because I had committed to
helping my daughter move apartments (why oh why did I do this to myself?).
This morning, I'm sitting in a cafe working on a song that will be released
later this month.
OZ Schnozz
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