◑ Photo editing

Exposure

노출

Multiplies overall brightness up or down in stops (powers of two) — the most basic tone adjustment there is.

Also known as: Exposure compensation노출 보정

···

html

<div class="wrap">
  <div class="stage"><canvas id="c" width="300" height="180"></canvas></div>
  <div class="hud"><b id="ev">+0.0 EV</b><span>왼쪽 원본 / 오른쪽 보정</span></div>
</div>

css

.wrap{position:absolute;inset:0;padding:clamp(8px,3vmin,20px);display:flex;flex-direction:column;gap:6px}
.stage{position:relative;flex:1;min-height:0}
canvas{position:absolute;inset:0;width:100%;height:100%;object-fit:contain;border-radius:10px;border:1px solid var(--line);background:#0a0a0a}
.hud{display:flex;justify-content:space-between;gap:8px;font:700 clamp(9px,2.2vmin,11px)/1 ui-monospace,monospace;color:var(--muted)}
.hud b{color:var(--fg)}

js

var W = 300, H = 180;
var c = document.getElementById('c'), ctx = c.getContext('2d');

function paintPhoto(cx, w, h) {
  var g = cx.createLinearGradient(0, 0, 0, h * 0.62);
  g.addColorStop(0, '#5b86c9'); g.addColorStop(0.55, '#bcd6ea'); g.addColorStop(1, '#f5e0ad');
  cx.fillStyle = g; cx.fillRect(0, 0, w, h);
  var sx = w * 0.74, sy = h * 0.22, sr = h * 0.11;
  var sg = cx.createRadialGradient(sx, sy, 0, sx, sy, sr * 3.2);
  sg.addColorStop(0, 'rgba(255,247,214,0.9)'); sg.addColorStop(1, 'rgba(255,247,214,0)');
  cx.fillStyle = sg; cx.fillRect(0, 0, w, h * 0.62);
  cx.fillStyle = '#fff8df'; cx.beginPath(); cx.arc(sx, sy, sr, 0, 7); cx.fill();
  cx.fillStyle = '#6f9152';
  cx.beginPath(); cx.moveTo(0, h * 0.64);
  for (var x = 0; x <= w; x += 14) cx.lineTo(x, h * 0.64 - Math.sin(x * 0.014) * h * 0.05 - Math.sin(x * 0.032 + 1.2) * h * 0.02);
  cx.lineTo(w, h); cx.lineTo(0, h); cx.closePath(); cx.fill();
  cx.fillStyle = '#405f38';
  cx.beginPath(); cx.moveTo(0, h * 0.79);
  for (var x2 = 0; x2 <= w; x2 += 14) cx.lineTo(x2, h * 0.79 - Math.sin(x2 * 0.022 + 0.6) * h * 0.035);
  cx.lineTo(w, h); cx.lineTo(0, h); cx.closePath(); cx.fill();
  var tx = w * 0.2, ty = h * 0.8;
  cx.strokeStyle = '#3a2a1c'; cx.lineWidth = Math.max(1.5, w * 0.008);
  cx.beginPath(); cx.moveTo(tx, ty); cx.lineTo(tx - w * 0.01, ty - h * 0.13); cx.stroke();
  cx.fillStyle = '#2e4a28';
  for (var i = 0; i < 5; i++) { cx.beginPath(); cx.arc(tx + (i - 2) * w * 0.013, ty - h * 0.15 - (i % 2) * h * 0.018, w * 0.028, 0, 7); cx.fill(); }
  cx.fillStyle = '#1e1e1c';
  cx.beginPath(); cx.arc(w * 0.56, h * 0.745, h * 0.018, 0, 7); cx.fill();
  cx.fillRect(w * 0.555, h * 0.76, w * 0.01, h * 0.06);
  var img = cx.getImageData(0, 0, w, h), d = img.data;
  for (var p = 0; p < d.length; p += 4) { var n = (Math.random() - 0.5) * 10; d[p] += n; d[p + 1] += n; d[p + 2] += n; }
  cx.putImageData(img, 0, 0);
}
paintPhoto(ctx, W, H);
var orig = ctx.getImageData(0, 0, W, H);
var t = 0;
function frame() {
  t += 0.02;
  var ev = Math.sin(t) * 1.3;
  var factor = Math.pow(2, ev);
  var lut = new Uint8ClampedArray(256);
  for (var v = 0; v < 256; v++) lut[v] = Math.min(255, Math.round(v * factor));
  var out = ctx.createImageData(W, H);
  var od = out.data, id = orig.data;
  for (var i = 0; i < id.length; i += 4) { od[i] = lut[id[i]]; od[i + 1] = lut[id[i + 1]]; od[i + 2] = lut[id[i + 2]]; od[i + 3] = 255; }
  ctx.putImageData(out, 0, 0);
  var frac = (Math.sin(t * 0.6) + 1) / 2 * 0.7 + 0.15;
  var sw = Math.round(W * frac);
  if (sw > 0) ctx.putImageData(orig, 0, 0, 0, 0, sw, H);
  ctx.strokeStyle = '#fff'; ctx.lineWidth = 2; ctx.beginPath(); ctx.moveTo(sw, 0); ctx.lineTo(sw, H); ctx.stroke();
  document.getElementById('ev').textContent = (ev >= 0 ? '+' : '') + ev.toFixed(1) + ' EV';
  requestAnimationFrame(frame);
}
frame();

Exposure compensation is a linear multiply applied to every pixel by the same factor. +1 stop doubles every value, -1 stop halves it. This demo bakes that factor into a lookup table, multiplies each pixel through it, and clamps at 255 — unlike a levels gamma curve, midtones and highlights all move by the identical ratio.

Use it as the first, broad-strokes fix when a shot came out uniformly a bit dark or bright. RAW files tolerate this multiply with little detail loss since the sensor recorded more range than the preview shows; an already-compressed JPEG has much less headroom.

Push it up too far and highlights that were already bright collapse into flat white (clipping); push it down and shadow noise becomes obvious. If you only want to brighten part of the frame, that's a job for levels, curves or a mask — exposure moves everything by the same amount.

When to use

Use it as the first pass when the whole frame is uniformly off. To brighten only part of it, use a mask or curve instead.