Mmm wouldn't a proper PS conversion to 8bit cure the problem and saving later to 8bit Jpeg rather than 16bit image directly exported to 8bit Jpeg ?
2011/6/2 Bruce Walker <[email protected]>: > 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 > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and > follow the directions. > -- Thibault Massart aka Thibouille/Thibs ---------------------- Photo: K-7, Sigma 28/1.8 macro, FA50/1.4, DA40Ltd, K30/2.8, DA16-45, DA50-135, DA50-200, 360FGZ KX, MX, SuperA+Motor, Z1, P30 Mamiya C330+80/2.8 Sekonic L-208 FalconEyes TE300D x2 Studio flashes Laptop: Macbook 13" Unibody SnowLeo/Win7 Programing: Delphi 2009 -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
