指数

html,
body,
svg {
  height: 100%;
}

<svg viewBox="0 0 420 200" xmlns="http://www.w3.org/2000/svg">
  <defs>
    <linearGradient
      id="gradient"
      gradientUnits="userSpaceOnUse"
      x1="0"
      y1="0"
      x2="200"
      y2="0">
      <stop offset="0" stop-color="#ff0000" />
      <stop offset="0.5" stop-color="#00ff00" />
      <stop offset="1" stop-color="#0000ff" />
    </linearGradient>
  </defs>

  <filter id="componentTransfer1" x="0" y="0" width="100%" height="100%">
    <feComponentTransfer>
      <feFuncR type="gamma" exponent="1" />
      <feFuncG type="gamma" exponent="1" />
      <feFuncB type="gamma" exponent="1" />
    </feComponentTransfer>
  </filter>
  <filter id="componentTransfer2" x="0" y="0" width="100%" height="100%">
    <feComponentTransfer>
      <feFuncR type="gamma" exponent="5" />
      <feFuncG type="gamma" exponent="5" />
      <feFuncB type="gamma" exponent="5" />
    </feComponentTransfer>
  </filter>

  <rect
    x="0"
    y="0"
    width="200"
    height="200"
    fill="url(#gradient)"
    style="filter: url(#componentTransfer1);" />
  <rect
    x="0"
    y="0"
    width="200"
    height="200"
    fill="url(#gradient)"
    style="filter: url(#componentTransfer2); transform: translateX(220px);" />
</svg>