Many thanks for the explanation...............I learned something.
----- Original Message -----From: Moose <olymoose@xxxxxxxxx>To: Olympus Camera
Discussion <olympus@xxxxxxxxxxxxxxxxx>Sent: Fri, 18 Apr 2014 08:58:38 -0000
(UTC)Subject: Re: [OM] 2014 Orchid Show
On 4/17/2014 5:15 PM, DZDub wrote:> Thanks Moose and Chris. I worked quite hard
on them.
And it's a really first rate gallery!
> Are you certain that they should not look as I have rendered them?
"Should" is a tricky word. If you think they look the way they should, you are
right.
I do believe that a rendition more true to the original subject is possible.
It's entirely possible that you did a perfect job - right up until downsampling
and/or conversion from aRGB to sRGB, either by you or the gallery software. I
have certainly had many cases where downsampling has caused clipping of what
was a perfect histogram at full size. I've also had occasional trouble, with a
'hot' red channel, in particular, with conversion for the web. Some traffic
cones drove me wacko a few years ago.
I don't consider what I did to be a complete solution. That's not possible with
these JPEGs. It's intended only as an illustration, to show in which directions
highlight retention will take images.
> If so, what convinces you of it?
It's obvious to my eye. I probably wouldn't have said anything, but for Chris
apparently seeing the same thing and commenting on it as something possibly
unavoidable. I see blown red channels on red-orange-yellow flowers on the web
(and in print) all the time. If I mentioned every instance I see posted here,
I'd be much more annoying than I already am. :-) As I said, it's a great
looking gallery, with a few, relatively minor, flaws in red channels.
It's also obvious, and easier to explain, in the histograms, so let me start
there.
<http://www.moosemystic.net/Gallery/Others/Wilcox/Orchid_Red_Channels.htm>
I hope it's easy to see the clipped red channels. The big bump of red against
the right that turns into a tall red line at the very end. There's only so much
I can do with a clipped JPEG, so I left a little clipping on the red one, to
avoid making the image look funny. I'm really only stretching out compressed
highlights. The ones that are well and truly clipped to 255 can't be fixed.
As to viewing:
On the red one, notice the slight overall change of color. It appears to my eye
that it is a more natural shade of flower red. In any case, the histo confirms
at least that the color is wrong. It's always wrong if a channel is clipped.
Assume an area of red is r245, b200, g180, that proportion gives a certain
color. If you lower them all proportionately, the shade remains the same, but
darker. If you raise them all proportionately, and the red clips, the mix of
color channels changes, and so does the color.
You can see where the recovery is incomplete where the color changes less, as
just to the sides of the central veins of the petals
A second effect, both of clipping and of JPEG engines/conversions that compress
the top of the histogram, is a loss of visual detail. The variations in the red
channel that help define details of the subject all go to the same or only very
slightly different colors, and the detail disappears.
You can see the effect pretty clearly in the detail of the vein structure. Also
in the rough, grainy structure of the underside of the orange ones. In both
cases, there are still areas where tonal detail was not recoverable, and thus
they remain without detail.
Does that answer your question?
Shaggy Moose
-- What if the Hokey Pokey *IS* what it's all about?--
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