Thanks alot for taking the time to post this very informative post. All make sense now
Thanks everyone! -- Hugo Leveille Compositing TD Vision Globale [email protected] Sent from my iPhone On Apr 22, 2011, at 4:08 AM, "Tahl Niran" <[email protected]> wrote: > I think I am skirting the realm of what I can say in a public forum as a lot > of this is company specific. The Josh Pines style conversion will avoid > negative values the resulting linearised file, and it will also ensure that > middle grey ( log code value 445) will be converted to a linear value of .18 > or to use the photographic term 18% grey. If you have a copy of Marcie handy > you can use the 445 swatch and see this. Its pretty crucial. > > As Jonathan pointed out negative values are to be avoided in almost all > standard image manipulation operations, you do not want to have negative > values coming into merges and other things like keyers. > > Now for the necessarily vague answers > > As grain in a linear space results in both and additive and subtractive > effects on pixels you will want to ensure that you are not generating > negative values when you grain. Many people cited this as a reason for going > back to log in thqe old Shake days but there are definitely simple work > arounds if you are using grain tools which expect linear inputs. > > Generally speaking Gamma coorection of any sort on an image is to be avoided > at all costs, this includes the type of pedastal correction that you are > speaking about. It is much simpler to just raise values by a nominal amount > and then adjust your vLUT to compensate rather than introduce an non-linear > curve into a linear compositing space. If you are going to comp film anyway > most people are working with a 3d film output lut rather than the default > sRGB. > > > Subject: Re: [Nuke-users] Grade clamping > > From: [email protected] > > Date: Thu, 21 Apr 2011 19:34:10 -0700 > > To: [email protected] > > > > So, after your read node, drop a grade node in the tree. Set the offset to > > .03. This will make everything washed out, so set your gamma to, say, 0.8. > > Season to taste with this. When you get it dialed, take the same grade > > node, copy it, and paste it right before your write node. Open up the node > > to view the properties, and put a check in the "reverse" box. > > > > When working with the footage, it's going to look slightly different than > > the original plate, and a little lifted. This won't matter, you'll be > > reversing the grade out at the end of your comp, so your VFX supe won't > > know the difference, and your negative code values will be preserved. > > > > > > On Apr 21, 2011, at 7:17 PM, Hugo Leveille wrote: > > > > > Degraining step involve more data on the server and quality loss at some > > > point > > > > > > Might be acceptable on some project, but with some project where the vfx > > > sup won't even watch the comp in dailies if there is a difference with > > > the original plate (figurely speaking) it won't do it > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > Hugo Leveille > > > Compositing TD > > > Vision Globale > > > [email protected] > > > > > > Sent from my iPhone > > > > > > On Apr 21, 2011, at 10:08 PM, "Brad Friedman" <[email protected]> wrote: > > > > > >> Proper grain management includes a degraining step and a regrain step. > > >> > > >> On Apr 21, 2011, at 10:05 PM, chris <[email protected]> wrote: > > >> > > >>> On 4/21/11 at 3:18 AM, [email protected] (Brad Friedman) wrote: > > >>>> You probably should not even be applying a grade node > > >>>> before grain management. No sense color correcting values > > >>>> that are chemical noise. The question is: what is your > > >>>> d-min value after proper degraining? > > >>> > > >>> actually in this case we want to keep the grain, that's why > > >>> it's shot on film ;) > > >>> > > >>> and i don't want to color correct it, i just want to keep it > > >>> unaffected through the pipeline. obviously if the sub 95 > > >>> values are clamped by the filmrecorder in the end, then this > > >>> is a moot point (guess the only way to be sure is to ask the > > >>> guys who are operating the recorder) ... but there are still > > >>> situations where we want to keep the unclipped data, even if > > >>> it's only grain texture (like adding a lens flare, which > > >>> would bring up the sub 95 values to something visible). > > >>> > > >>> ++ chris > > >>> > > >>> ps: tried to build the pdx formulas in nuke if anybody is > > >>> interested in playing around.. hope i didnt mess things up: > > >>> > > >>> set cut_paste_input [stack 0] > > >>> push $cut_paste_input > > >>> Expression { > > >>> temp_name0 pdxLogReference > > >>> temp_expr0 455 > > >>> temp_name1 pdxDensityPerCodeValue > > >>> temp_expr1 0.002 > > >>> temp_name2 pdxNegativeGamma > > >>> temp_expr2 0.6 > > >>> temp_name3 pdxLinReference > > >>> temp_expr3 0.18 > > >>> expr0 "pow(10, ((red * 1023 - pdxLogReference) * > > >>> pdxDensityPerCodeValue/pdxNegativeGamma)) * pdxLinReference" > > >>> expr1 "pow(10, ((green * 1023 - pdxLogReference) * > > >>> pdxDensityPerCodeValue/pdxNegativeGamma)) * pdxLinReference" > > >>> expr2 "pow(10, ((blue * 1023 - pdxLogReference) * > > >>> pdxDensityPerCodeValue/pdxNegativeGamma)) * pdxLinReference" > > >>> name pdxLog2Lin > > >>> selected true > > >>> xpos -430 > > >>> ypos -118 > > >>> } > > >>> Expression { > > >>> temp_name0 pdxLogReference > > >>> temp_expr0 455 > > >>> temp_name1 pdxDensityPerCodeValue > > >>> temp_expr1 0.002 > > >>> temp_name2 pdxNegativeGamma > > >>> temp_expr2 0.6 > > >>> temp_name3 pdxLinReference > > >>> temp_expr3 0.18 > > >>> expr0 "(pdxLogReference + log10( max( red, 0.00000001 ) / > > >>> pdxLinReference )*pdxNegativeGamma/pdxDensityPerCodeValue) / 1023" > > >>> expr1 "(pdxLogReference + log10( max( green, 0.00000001 ) / > > >>> pdxLinReference )*pdxNegativeGamma/pdxDensityPerCodeValue) / 1023" > > >>> expr2 "(pdxLogReference + log10( max( blue, 0.00000001 ) / > > >>> pdxLinReference )*pdxNegativeGamma/pdxDensityPerCodeValue) / 1023" > > >>> name pdxLin2Log > > >>> selected true > > >>> xpos -430 > > >>> ypos -74 > > >>> } > > >>> > > >>> _______________________________________________ > > >>> Nuke-users mailing list > > >>> [email protected] > > >>> http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users > > >> _______________________________________________ > > >> Nuke-users mailing list > > >> [email protected] > > >> http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users > > > _______________________________________________ > > > Nuke-users mailing list > > > [email protected] > > > http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users > > > > _______________________________________________ > > Nuke-users mailing list > > [email protected] > > http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users > _______________________________________________ > Nuke-users mailing list > [email protected] > http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users _______________________________________________ Nuke-users mailing list [email protected] http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-users
