Meanwhile, Dado Valentic has already implemented it in Look Designer for Resolve Studio.

Hey everybody,

It shouldn't be too hard to get this working as a DCTL until we have native support in DaVinci. I put together a quick showcase for Alexa LogC3 only.

Is there any detailed technical documentation on how to implement this correctly?

• How large are the zones for those "extra stops"?

• What is considered over- or underexposed? The example on the landing page showed clipping in areas where there is still detail.

• How do you derive the luminance channel? In my example, I converted to linear and then AWG to XYZ, using the Y channel to calculate the zones.

• What are the exact RGB values for the zones? I just color-picked them from the webpage for now.

If there's interest, I can add more transfer functions or working spaces like ACES or DaVinciWG - unless that's already in the works?

// Created by Valentin Bernauer 

// user inputs 

DEFINE_UI_PARAMS(color_space, Working Color Space, DCTLUI_COMBO_BOX, 0, {alexalogc3__alexawidegamut}, {Alexa Log3/Wide Gamut})

__DEVICE__ float3 logc3_to_linear(float3 rgb)
{
    const float r = rgb.x > 0.1496582f ? (_powf(10.0f, (rgb.x - 0.385537f) / 0.2471896f) - 0.052272f) / 5.555556f : (rgb.x - 0.092809f) / 5.367655f;
    const float g = rgb.y > 0.1496582f ? (_powf(10.0f, (rgb.y - 0.385537f) / 0.2471896f) - 0.052272f) / 5.555556f : (rgb.y - 0.092809f) / 5.367655f;
    const float b = rgb.z > 0.1496582f ? (_powf(10.0f, (rgb.z - 0.385537f) / 0.2471896f) - 0.052272f) / 5.555556f : (rgb.z - 0.092809f) / 5.367655f;
    return make_float3(r,g,b);
}

// alexawidegamut3rgb_to_xyz
__DEVICE__ float3 alexawidegamut3rgb_to_xyz(float3 rgb)
{
    float r = (rgb.x * 0.638008 ) + (rgb.y * 0.214704) + (rgb.z * 0.097744);
    float g = (rgb.x * 0.291954 ) + (rgb.y * 0.823841 ) + (rgb.z * -0.115795);
    float b = (rgb.x * 0.002798  ) + (rgb.y * -0.067034) + (rgb.z * 1.153294);
    return make_float3(r, g, b);
}

__DEVICE__ float3 transform(int p_Width, int p_Height, int p_X, int p_Y, float p_R, float p_G, float p_B)
{

float r = p_R; 
float g = p_G;
float b = p_B;
float3 rgb = make_float3(r,g,b);	

rgb = logc3_to_linear(rgb); 
rgb = alexawidegamut3rgb_to_xyz(rgb); 
float Y = rgb.y; 


// Exposure stops relative to middle gray (0.18)
#define EV_N10 0.00017578125f  // 0.18 * pow(2,-10)
#define EV_N6  0.0028125f      // 0.18 * pow(2,-6)
#define EV_N5  0.005625f       // 0.18 * pow(2,-5)
#define EV_N4  0.01125f        // 0.18 * pow(2,-4)
#define EV_N3  0.0225f         // 0.18 * pow(2,-3)
#define EV_N2  0.045f          // 0.18 * pow(2,-2)
#define EV_N1  0.090f          // 0.18 * pow(2,-1)
#define EV_N05 0.1272792f      // 0.18 * pow(2,-0.5)
#define EV_05  0.2545584f      // 0.18 * pow(2,0.5)
#define EV_1   0.36f           // 0.18 * pow(2,1)
#define EV_2   0.72f           // 0.18 * pow(2,2)
#define EV_3   1.44f           // 0.18 * pow(2,3)
#define EV_4   2.88f           // 0.18 * pow(2,4)
#define EV_5   5.76f           // 0.18 * pow(2,5)
#define EV_6   11.52f          // 0.18 * pow(2,6)
#define EV_10  184.32f         // 0.18 * pow(2,10)

// Zones 
if (Y < EV_N10 ){rgb = make_float3(0.0, 0.0, 0.0);}
else if (Y >= EV_N10 && Y < EV_N6 ){rgb = make_float3(0.397, 0.285, 0.618);}
else if (Y >= EV_N6 && Y < EV_N5){rgb = make_float3(0.634, 0.509, 0.742);}
else if (Y >= EV_N5 && Y < EV_N4){rgb = make_float3(0.096, 0.465, 0.666);}
else if (Y >= EV_N4 && Y < EV_N3){rgb = make_float3(0.160, 0.698, 0.915);}
else if (Y >= EV_N3 && Y < EV_N2){rgb = make_float3(0.112, 0.670, 0.297);}
else if (Y >= EV_N2 && Y < EV_N1){rgb = make_float3(0.372, 0.748, 0.285);}
else if (Y >= EV_N1 && Y < EV_N05){rgb = make_float3(0.594, 0.802, 0.253);}

else if (Y >= EV_N05 && Y < EV_05){rgb = make_float3(0.5, 0.5, 0.5);}

else if (Y >= EV_05 && Y < EV_1){rgb = make_float3(1.0, 0.931, 0.04);}
else if (Y >= EV_1 && Y < EV_2){rgb = make_float3(1.0, 0.995, 0.670);}
else if (Y >= EV_2 && Y < EV_3){rgb = make_float3(0.978, 0.445, 0.168);}
else if (Y >= EV_3 && Y < EV_4){rgb = make_float3(0.991, 0.677, 0.288);}
else if (Y >= EV_4 && Y < EV_5){rgb = make_float3(0.955, 0.112, 0.148);}
else if (Y >= EV_5 && Y < EV_6){rgb = make_float3(0.911, 0.505, 0.562);}
else if (Y >= EV_6 && Y < EV_10){rgb = make_float3(0.975, 0.762, 0.770);}
else if (Y > EV_10 ){rgb = make_float3(1.0, 1.0, 1.0);}

return rgb; 
}

Very interested in this as well for standardization. Any update?

Thank you for bringing the EL Lachman Zone System to the cinematography and postproduction field. Indeed, it's an invaluable tool, especially when implementing a logarithmic scale system. I’m glad the system is already implemented in Dado Valentic’s Look Designer in Davinci Resolve. I hope others in post-production will support this implementation.

Is it possible to use the EL Lachman Zone System on-set and in post-production in HDR workflow?

Chris,

Thanks for your question.

Yes, we've been in discussions with manufacturers about how to implement the EL Zone System into post production.

Will post updates here on the site as things progress.

Stay tuned for updates.