Tag Archives: Lift

Color Grading with Blender 2.5

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Introduction

Yeahh Matt Ebb just commit my patch (SVN r27733) for the “Color Balance” node in Blender 2.5 Compositing node !!! Now it should be much easier to work with.

You can get a version of blender at Graphicall.org (any version above revision 27733)

There is still some precision issue on the color wheels, I guess some day it will be possible to move the color picker slower.



How to use it ?

First I would recommend you to un-check the “color management” setting in Blender 2.5 or it will make the blacks really hard to control.

If you are not so familiar with color grading, and push-pull techniques, I would really recommend you to watch Stu Maschwitz’s (Prolost) video tutorial using Magic Bullet Colorista. The settings won’t be exactly the same, but the approach quite the same though !

Red Giant TV Episode 22: Creating a Summer Blockbuster Film Look from Stu Maschwitz on Vimeo.


How does it works ?

I described the Lift/Gamma/Gain in a previous post, and mostly this node is based on the formulas specified there. We just slightly modified it so the 3 defaults values parameters are equal to 1.0 just like in Colorista. Which makes it much easier to control the blacks.
Actually the “Color Balance” node before this revision was the same formula but with lift default value equal to 0.0


Some presets !

While making some comparison test between Colorista in After Fx and the “color balance” node in blender, I tried to mimic some of Colorista’s presets.
You can download the “Blender Color Grading Presets” here : http://code.google.com/p/ft-projects/downloads/list

There is the following presets :

Bleach preset w/ Color Balance node

Cold preset w/ Color Balance node

Cool to Warm preset w/ Color Balance node

Day to Night preset w/ Color Balance node

Punchy preset w/ Color Balance node

vignetting using Mike Pan's approach


Blender Quick Tips : How to create masks in the compositing editor

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Since there is no mask in the “Compositing Editor” of Blender yet, I found a simple tricks which could work pretty well especially in case of color grading.

You’ll see nothing really fancy here since the mask can only be square (or pretty close to a square shape though). But if you check out Colorista for instance, the two allowed shapes are ellipse and rectangle.

Blender Quick Tips : How to create masks in the compositing editor from François Tarlier on Vimeo.

Exposure/Offset/Gamma photoshop tool to Shaders

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The goal here was to understand how works the Exposure feature of Photoshop for my research on lift/gamma/gain

exposure-photoshop-panel

NB : I wouldn’t say I’m an 100% sure about how it works, but that’s how I understood it worked so far


Exposure :

I though exposure was more complicated than that (maybe it is) but the way I’m reproducing it, is only by adding a percentage of the pixel by himself. nothing more complicated than that.


Offset :

As seen in my previous post, the Offset is just an Add of a value. My first approach on it was saying Offset is controlling the luminance of it, so I guess the correct way would be to convert the pixel in the YCbCr color space, add a value to the Y channel, and reconverting back to RBG color space. But this is doing a lot of calculation for nothing, while adding just a value to the entire picture would probably do the same, and actually would correspond to the Lift (or Offset of the CDL).
Plus switching between color space makes you loose some tiny precision in the color.

Anyway, I’ll give the two solutions, please let me know if you think one is better than the other


Gamma :


As usual, power(1/gamma)

The right order :

If all this was actually all pretty simple, at least I learned one thing (obvious as well I must say). Don’t forget to do the operation in the right order. In my first try I had a small bug, and couldn’t have the same result in Photoshop & in my shader, because I was doing the offset before the exposure. Which is pretty silly, since if you do that, you are loosing all the dynamic range of your picture when you actually want to have as much information as you can for your exposure.

The order is Exposure -> Offset -> Gamma.


Formula :

output = ((input*exposure) + offset)^(1/gamma)

hum… looks a lot like the CDL formula doesn’t it ? :) Except exposure is a single float value between 0 and 20 ? (maybe more, maybe less depends of your picture)and the default value should be 1.The offset should be between -10 ? and 1 I think.


Shaders (HLSL in Media Player Classic) :

http://www.pasteall.org/8868/c

Here I’m giving the version with YCbCr conversion, but I’m pretty sure it is not doing anything more than the above one, except loosing information in conversion. But at least it shows the YCbCr conversion :)

http://www.pasteall.org/8869/c

lift/gamma/gain VS. ASC CDL

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Following my previous post “lift-gamma-gain color correction formula with blender compositing” I continue my research about all those formulas.

Comparison

I came to compare the ASC CDL (American Society of Cinematographers Color Decision List) formula to the Lift/Gamma/Gain formula I found on Blender.org

Here are the results :

lift-vs-cdl-image

lift-vs-cdl-gradient

Where the formula are :

  • CDL : ((input*slope)+offset)^(1/gamma)
  • Lift :  gain * (input + lift * (1 – input)^(1/gamma))

(slope = gain ; offset = lift)

You can see that CDL is able to burn (exposure) the white, while the Lift will keep the white unchanged as much as it can.
_dbr did a nice test for me in Shake and create a graph that really shows the differences

lift-vs-cdl-curve

so in both formula by only changing Lift/Offset, you can see clearly that the lift keep the white unchanged while CDL push the black and white as well.

HLSL Shader in Media Player Classic

Yes, in Media Player Classic, you can write shaders compiled in runtime while you are watching your favourite TV Shows ^^ . Awesome !!!


hlsl code on Pasteall.org



Conclusion

So I guess CDL is much easier to use, but I believe that Lift could give you much control other the image. What would need Lift to be able to push the white as well would be an exposure parameter! (which is the goal of my next shader :) )

lift-gamma-gain color correction formula with blender compositing

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I got lately interest in Lift/Gamma/Gain formula for some personal project, I thought I would share some of the informations I found.

What does Lift/Gamma/Gain ?



Lift/Gamma/Gain is actually is a really nice approach for color correction in my opinion. Lift/Gamma/Gain are actually controlling the Shadows/Mid-tones/High-tones of your picture with the ability to offset the colors.
This combine with saturation and exposure could give a powerful tool for color correction. This is the kind of tool you’ll find in plug-in such as Magic Bullet Colorista from Red Giant Software or professional hardware as Black Magic DaVinci


Stu Maschwitz from Prolost did a nice tutorial on how to use his Colorista plug-in

Red Giant TV Episode 22: Creating a Summer Blockbuster Film Look from Stu Maschwitz on Vimeo.

Mirror of http://www.redgiantsoftware.com/videos/redgianttv/item/23/



Lift/Gamma/Gain formula


outputColor = (gainColor*(inputColor+liftColor*(1-inputColor)))^(1/gammaColor)

This has to be done for each channel color for each pixels of your picture.


To make some test of this formula I did use Blender’s compositing and its “Math” node which was pretty useful :) . This operation is useless since it is terribly slow using nodes and it’s already implemented in the Sequencer (properties of the strip), but it’s just for the test !

Here is the blend file and a screenshot :

Lift/Gamma/Gain Formula done in Blender Compositing using "Math" node

Lift/Gamma/Gain Formula done in Blender Compositing using "Math" node