On 11-06-02 3:11 AM, Tim Bray wrote:
Check out
http://www.tbray.org/ongoing/When/201x/2011/06/01/-big/RUNE0790.jpg.html
Look at the green bokeh-fied background and observe the obvious lines
that look like elevation lines on a map, let's call them "bars", as
the green brightness drops off. They ain't there in the .dng, and
after the first cut, I specified 100% JPG quality and they're still
obvious.
It gets weird... I took a screen grab of the Lightroom window, in
which none of those bars are visible, and saved to a .png file, using
built-in OS X facilities, the PNG created by Preview. Obvious bars! I
put it online at http://www.tbray.org/tmp/screen-grab.png - I thought
.png was uncompressed!
PNG is not lossy like JPEG, but it is compressed. The compression is not
as efficient as JPEG because it can't play tricks that lossy conversions
can.
I'm sure that a silky-smooth jpg of this picture could be created.
But I don't know how.
-Tim
I'm barely seeing your bars; they are not *that* obvious.
Assuming your toolchain is 100% 16-bit (or better) end-to-end, then your
image is suffering from banding by being dithered down to 8-bits at the
output. JPEG is 8-bits RGB, so you are most likely introducing banding
right there.
Also as for your PNG image, there's 16-bit PNG and 8-bit PNG, and you
used 8-bit, which will show clear banding same as the JPEG.
screen-grab.png: PNG image, 764 x 727, 8-bit/color RGB, non-interlaced
Even 16-bit images can suffer from very slight banding in really gradual
tonal transitions. The solution to that is to dither the image a bit --
add some intentional noise. You could use a mask in Photoshop to
restrict the noise addition to just the darker bokeh areas and avoid
mucking-up the bloom.
There's a grain feature in LR (bottom of the Develop section) that you
could play with to add some noise.
And that's a _great_ shot, btw. My only issue with it is I can't see the
stem which makes it look a little "floating in space", but I guess
that's because of the angle of view. You've struck an excellent balance
with the DoF / sharp edges / bokeh.
-bmw
--
PDML Pentax-Discuss Mail List
PDML@pdml.net
http://pdml.net/mailman/listinfo/pdml_pdml.net
to UNSUBSCRIBE from the PDML, please visit the link directly above and follow
the directions.
