One curiosity I have about the new module is the color correction is four ways (offset / lift / power / gain), while the old module was three ways (slope / offset / power or lift / gamma / gain).
Three parameters are associated to shadows / midtones / highlights, so what about the fourth ?
Thanks for the clarification. So thatâs why lowpass module is before color balance. In its output it says âspecial, lab, scene-referredâ. Does that mean, to stay in scene-reffered workspace, that you should then use blend modes from the âRGB (scene)â blend color space?
Given this statement from the manual I think that would make sense
Note: When using blend modes on any module, you should be aware that many of the blend modes are optimized for display-referred space and assume a mid-gray value of 50%. For the linear scene-referred space, stick with blend modes based on arithmetic operations (addition, multiplication, division, subtraction, average), on maximum/minimum comparisons (screen) or on channel separations (hue, color, chroma, etc.).
3 Likes
However, there are some blend modes available to both âRGB (display)â and âRGB (scene)â: Addition, Subtract, Multiply, Difference, Average, Lightness, Chroma
Is there any difference between the blend modes familiar to both?
When in scene-referred part of pipeline (pre-filmic) we obviously stick to âRGB (scene)â blend modes. But how about after filmic? Eg. modules like Local Contrast, should we use âRGB (display)â for those? And what if we move a scene module such as Exposure after Filmic to perform a Multiply blend. Does it matter whether that blend is done in âRGB (display)â or âRGB (scene)â?
This also leads to parametric mask questions. Pre-Filmic, I guess middle grey of âgâ slider is 18. But after Filmic, is middle grey of âgâ slider now 50?
Well try this oneâŠtake the rgb tone curveâŠdonât do anything âŠblend it on an image in display referred subtract and scene referred subtractâŠmaybe try around 10%âŠthe effect in display is way strongerâŠso even subtract does not equal subtract. I think the math is a bit different in the way it is applied. Someone familiar with the code or the nuance of this could comment its just an obervationâŠ
1 Like
Now i am confused. So i shouldnât put any module between filmic and output profile? I did this with modules i used to do some dodging and burning or with the local contrast module.
I did a test. First applied exposure and filmic. Then applied 2nd instance of exposure, blend mode âmultiplyâ, first in âRGB (scene)â then in âRGB (display)â. Result was identical. Then moved 2nd instance of exposure after filmic. Again both âRGB (scene)â and âRGB (display)â matched. So for that blend mode, the math appears to be the same. The effect is of course different applying it before and after filmic.
Using parametric mask, I then slid shadow sliders up to 18 (mid grey).
âgâ in âRGB (scene)â gives very similar results to
âgâ in âRGB (display)â, and
âLâ in âRGB (display)â, but gives completely different results to
âJzâ in âRGB (scene)â. In order for that to give similar results, the slider had to be moved up to 0.59
Testing all common blend modes on different modules, only âmultiplyâ and âaverageâ give identical results in âRGB (scene)â and âRGB (display)â, although âadditionâ was quite similar. Subtract, difference, lightness and chroma all gave different results. So for those 4 or 5, after filmic, I do not know whether it is âmore correctâ to use them in âRGB (display)â or âRGB (scene)â.
Iâm just going to use the default of the module and use my eyes. If you end up using mostly newer modules I think you will be offered the scene-referred blend modes for the most part. Perhaps not very scientific but with all the possible combinations introduced by moving modules around I am not going to try to keep track of itâŠ
2 Likes
No. Slope, offset and power, as well as lift, gamma and gain all had effect on the whole luminance range. Each of them only had a bit more weight, by algorithmic side-effects, on some sub-range. For example, slope/offset/power does:
\text{RGB}_{out} = ((\text{RGB}_{in} + \text{offset}) Ă \text{slope})^{\text{power}}
You see in the above formula that nothing actively separates luminances. The current formula does almost the same:
\text{RGB}_{out} = ((\text{RGB}_{in} + \text{global offset}) Ă \text{slope}(\text{luminance}))^{\text{power}}
Notice the difference is now that \text{slope} is a function of the variable luminance (Y), decomposed in 2 terms:
\text{slope}(Y) = (1 - \beta(Y)) \left((1 - \alpha(Y)) + \text{lift} Ă \alpha(Y)\right) + \text{gain} Ă \beta(Y)
where \alpha(Y) and \beta(Y) are the opacities of the shadows and highlights masks (itâs a simple alpha overlay of 2 layers, really).
TL;DR: the new 4 ways is only the old slope/offset/power where slope is split into lift and gain, and both are applied on different layers later overlayed with usual Porter-Duff âoverâ compositing operator.
But the offset and the power still have effect on the whole range, again with more weight on some subrange.
Multiply is a multiplication no matter in which space you do it⊠The algebraic operation doesnât change. What may change is the occurrence of clipping at 100% or not, and also if you multiply in Lab (which has a cubic root on), you obviously donât get the same result as if you multiply in linear.
Please state your space. After and before filmic, middle-grey is at 18% linear. Filmic preserves middle-grey unchanged through its transform, it only shrinks or dilates the dynamic range around that pivot. 18% linear = 50% perceptual (in Lab, Lch, JzAzB etc.).
Think about the space you are in. Before filmic, you are in scene-referred space. After filmic, you are in display-referred space. Doing things in display-referred is unsafe and not output-agnostic, so you want to avoid it⊠but if you still want to use the display-referred modules in dt, you should put them in the display-referred part of the pipeline⊠waiting for these modules to get translated to scene-referred.
1 Like
Since middle grey is 18%, a.k.a. -2.45EV from 100% reflectance, is it correct that in order to use the multiply blend mode without affecting midtones (middle grey), one has to use a blend fulcrum of 2.45 EV, since multiplying something in linear space by 0.18 is the same as reducing exposure by 2.45 EV?
2 Likes
That is exactly what I was wondering.
Assuming 100% opacity, of course.
Yup.
1 Like
Is the official documentation of this module already in preparation? Where can it be found?
How is your French?? Aurelien did a video on itâŠen francais
I forget if it is about this version. Could you post the link for our convenience?
Uses the mask tab as wellâŠsadly I could not get good English subtitles⊠https://www.youtube.com/watch?v=qRLH5hMschs
I have also seen that that chapter of the dev version of the manual is empty, I thought I saw some draft some weeks ago - maybe it was deleted?
I know about AurĂ©liens video - stated to watch it some time ago, but didnât finish yet.
Thanks for the quick answers though.