Sentinel-2 L1C True Color Optimized

//VERSION=3

function setup() {
  return {
    input: ["B04", "B03", "B02", "dataMask"],
    output: { bands: 4 }
  };
}

// Contrast enhance / highlight compress


const maxR = 3.0; // max reflectance

const midR = 0.13;
const sat = 1.3;
const gamma = 2.3;

// remove the minimum Rayleigh scattering (check the Himalayas)

const ray = { r: 0.013, g: 0.024, b: 0.041 };

function evaluatePixel(smp) {
  const rgbLin = satEnh(sAdj(smp.B04 - ray.r), sAdj(smp.B03 - ray.g), sAdj(smp.B02 - ray.b));
  return [sRGB(rgbLin[0]), sRGB(rgbLin[1]), sRGB(rgbLin[2]), smp.dataMask];
}

const sAdj = (a) => adjGamma(adj(a, midR, 1, maxR));

const gOff = 0.01;
const gOffPow = Math.pow(gOff, gamma);
const gOffRange = Math.pow(1 + gOff, gamma) - gOffPow;

const adjGamma = (b) => (Math.pow((b + gOff), gamma) - gOffPow) / gOffRange;

// Saturation enhancement

function satEnh(r, g, b) {
  const avgS = (r + g + b) / 3.0 * (1 - sat);
  return [clip(avgS + r * sat), clip(avgS + g * sat), clip(avgS + b * sat)];
}

const clip = (s) => s < 0 ? 0 : s > 1 ? 1 : s;

//contrast enhancement with highlight compression

function adj(a, tx, ty, maxC) {
  var ar = clip(a / maxC, 0, 1);
  return ar * (ar * (tx / maxC + ty - 1) - ty) / (ar * (2 * tx / maxC - 1) - tx / maxC);
}

const sRGB = (c) => c <= 0.0031308 ? (12.92 * c) : (1.055 * Math.pow(c, 0.41666666666) - 0.055);

Evaluate and Visualize

• Copernicus Browser
• EO Browser

Description

True color composite uses visible light bands red, green and blue in the corresponding red, green and blue color channels, resulting in a natural colored product, that is a good representation of the Earth as humans would see it naturally. This visualization uses highlight compression to ensure no maxing-out of clouds or snow, adds the offset to the RGB reflectances to improve the contrast and the color vividness, uses sRGB encoding for no extra darkening of shadows and adds a small amount of saturation boost.

Description of representative images

Optimized True Color image of Rome. Acquired on 2023-01-30, processed by Sentinel Hub.