RECAP · 第一课讲过
白点：什么算「白」
白点是色彩标准里「什么算白」的约定：D50 · D55 · D65（约 6500K）· DCI。
白点不匹配，整片统一偏暖或偏冷——而且错得很一致，所以特别难发现。
第一课看过这张图，今天不重讲，只记一件事：白点错了，是原点错了，不是某个颜色错了。
RECAP · from session one
White point: what counts as white
The white point is the convention for what counts as white: D50, D55, D65 (about 6500 K), DCI.
Get it wrong and the whole frame goes warm or cool — consistently, which is exactly why it is so hard to spot.
You saw this in session one. We are not re-teaching it; just remember one thing: a wrong white point is the origin being wrong, not one colour being wrong.
零件 01 / 07 · LENS HOOD
遮光罩
套在镜头最前面的一圈遮光筒，把画面以外的斜射光挡在外面。
影响
斜光进了镜片会在片间反复反射，整幅发灰、出现光斑。画面发灰不一定是素材烂，也可能只是没装遮光罩。
斜光进了镜片会在片间反复反射，整幅发灰、出现光斑。画面发灰不一定是素材烂，也可能只是没装遮光罩。
真片帧 · 眩光示意（合成，非实拍漏光）
PART 01 / 07 · LENS HOOD
Lens hood
A tube in front of the glass that blocks light coming from outside the frame.
Affects
Stray light bounces between elements: contrast lifts and flare blooms. A washed-out frame is not always bad footage — sometimes it is just a camera without a hood.
Stray light bounces between elements: contrast lifts and flare blooms. A washed-out frame is not always bad footage — sometimes it is just a camera without a hood.
real frame · flare simulated (composite)
零件 02 / 07 · FRONT CELL
镜片组
真正成像的玻璃。焦距、最大光圈、像场都由它决定。
影响
焦距决定视角；像场必须盖住传感器，盖不住边角就是黑的。换镜头是换视角，不是换画质。
焦距决定视角；像场必须盖住传感器，盖不住边角就是黑的。换镜头是换视角，不是换画质。
真片帧 · 中心裁切模拟长焦视角（示意）
PART 02 / 07 · FRONT CELL
Front cell
The glass that actually forms the image. Focal length, maximum aperture and image circle all live here.
Affects
Focal length sets the field of view; the image circle has to cover the sensor or the corners go dark. Changing a lens changes the view, not the quality.
Focal length sets the field of view; the image circle has to cover the sensor or the corners go dark. Changing a lens changes the view, not the quality.
real frame · centre crop standing in for a long lens (simulated)
零件 03 / 07 · BARREL
镜筒
外筒、对焦环、光圈环。把玻璃固定在正确的位置上，并让你转动它们。
影响
对焦环移动的是焦点平面——清晰与虚化的那条分界线。焦点错了，后期救不回来，只能挨着用。
对焦环移动的是焦点平面——清晰与虚化的那条分界线。焦点错了，后期救不回来，只能挨着用。
真片帧 · 失焦示意（合成）
PART 03 / 07 · BARREL
Barrel
Outer tube, focus ring, iris ring — it holds the glass in the right place and lets you turn it.
Affects
The focus ring moves the plane of focus: the line between sharp and soft. Get it wrong and no grade brings it back.
The focus ring moves the plane of focus: the line between sharp and soft. Get it wrong and no grade brings it back.
real frame · defocus simulated (composite)
零件 04 / 07 · IRIS
光圈
多片叶片围成的可变圆孔，每档差 √2 倍面积。
影响
①进光量：f/1.4 到 f/16 差 128 倍 ②景深：孔越小景深越深 ③孔太小时反而变软（衍射）。光少了就得放大更多——这就是 ISO 和噪点的入口。
①进光量：f/1.4 到 f/16 差 128 倍 ②景深：孔越小景深越深 ③孔太小时反而变软（衍射）。光少了就得放大更多——这就是 ISO 和噪点的入口。
真片帧 · 降两档曝光示意（合成）
PART 04 / 07 · IRIS
Iris
A ring of blades forming a variable hole; each stop is √2 in area.
Affects
How much light gets in (f/1.4 to f/16 is 128×), how deep the depth of field goes, and — stopped right down — diffraction softening. Less light means more amplification: that is where ISO and noise enter.
How much light gets in (f/1.4 to f/16 is 128×), how deep the depth of field goes, and — stopped right down — diffraction softening. Less light means more amplification: that is where ISO and noise enter.
real frame · two stops down, simulated (composite)
零件 05 / 07 · MOUNT
卡口
镜头与机身之间的机械加电子接口，定义法兰距——卡口到传感器的距离。
影响
法兰距决定你能装哪些镜头、要不要转接环。转接会改法兰距，可能边角劣化、无限远不合焦；它同时把光圈和对焦指令从机身传给镜头。
法兰距决定你能装哪些镜头、要不要转接环。转接会改法兰距，可能边角劣化、无限远不合焦；它同时把光圈和对焦指令从机身传给镜头。
等距图局部 · 镜头端面与机身
PART 05 / 07 · MOUNT
Mount
The mechanical and electronic interface between lens and body. It defines the flange distance.
Affects
Flange distance decides which lenses fit and whether you need an adapter. Adapters shift it: soft corners, or no infinity focus. It also carries iris and focus commands from body to lens.
Flange distance decides which lenses fit and whether you need an adapter. Adapters shift it: soft corners, or no infinity focus. It also carries iris and focus commands from body to lens.
detail of the figure · lens end and body
零件 06 / 07 · BODY
机身
记录单元、散热、接口、监看。传感器装在它里面，但画面质量不归它管。
影响
机身决定记录格式：编码、位深、色度采样、码率。同一台机器录 ProRes 4444 和录 8bit 4:2:0，后期能调的余地完全不同——B 块和 D 块就是从这儿分出去的。
机身决定记录格式：编码、位深、色度采样、码率。同一台机器录 ProRes 4444 和录 8bit 4:2:0，后期能调的余地完全不同——B 块和 D 块就是从这儿分出去的。
等距图局部 · 机身记录单元
PART 06 / 07 · BODY
Body
Recorder, cooling, ports, monitoring. The sensor sits inside it, but image quality is not its job.
Affects
The body sets the recording format: codec, bit depth, chroma subsampling, bitrate. ProRes 4444 and 8-bit 4:2:0 out of the same camera leave very different room to grade.
The body sets the recording format: codec, bit depth, chroma subsampling, bitrate. ProRes 4444 and 8-bit 4:2:0 out of the same camera leave very different room to grade.
detail of the figure · the recording unit
零件 07 / 07 · SENSOR
CMOS
把光子变成电荷的硅片。每个像素都在数光子。
影响
①分辨率＝像素数 ②动态范围＝一个像素能装多少电荷 ③噪点＝光子少的时候统计涨落占比变大。读出电路把电荷放大多少倍就是 ISO——放大多少，噪点也一起放大。
①分辨率＝像素数 ②动态范围＝一个像素能装多少电荷 ③噪点＝光子少的时候统计涨落占比变大。读出电路把电荷放大多少倍就是 ISO——放大多少，噪点也一起放大。
真片帧 · 高 ISO 噪点示意（合成）
PART 07 / 07 · SENSOR
Sensor
A silicon chip turning photons into charge. Every pixel counts photons.
Affects
Resolution is pixel count; dynamic range is how much charge one pixel holds; noise is what happens when photons are few and the statistical spread dominates. How hard the readout amplifies that charge is ISO — and the noise is amplified with it.
Resolution is pixel count; dynamic range is how much charge one pixel holds; noise is what happens when photons are few and the statistical spread dominates. How hard the readout amplifies that charge is ISO — and the noise is amplified with it.
real frame · high-ISO noise simulated (composite)
地基 1 / 3 · 导览课讲过色深，这里只补一件事
位深：视频只用了 220 级
1920×1080 渐变素材 · 191 kbps · 同一组曲线
导览课讲过 256 / 1024 / 4096 级。这里补的是：视频级只占 16–235 这一段，所以 8bit 名义 256 级，实际只有约 220 级能用。
台阶不够 + 曲线拉得狠 = banding。拉曲线，等于把台阶之间的距离再拉开。
Foundation 1 / 3 · you had bit depth in the orientation; one thing to add
Bit depth: video only uses 220 of them
1920×1080 gradient · 191 kbps · same curve
The orientation covered 256 / 1024 / 4096. What is new here: video levels occupy only 16–235, so 8-bit has a nominal 256 but roughly 220 usable.
Too few steps plus a hard curve = banding. Pulling a curve stretches the distance between steps.
地基 2 / 3
码率 =
每秒给画面
多少数据
每秒给画面
多少数据
低码率一调就烂。
伪影是方形的、固定的；噪点是颗粒状的、随机的——伪影降噪没用，它是没有信息。
在哪设
拍：机器里选编码/压缩比 → 决定能调多狠
交：交付页 → 渲染设置 → 质量 → 决定文件多大
拍：机器里选编码/压缩比 → 决定能调多狠
交：交付页 → 渲染设置 → 质量 → 决定文件多大
同一帧、同一组调色 · 下排为 200% 放大
Foundation 2 / 3
Bitrate =
how much data
each second gets
how much data
each second gets
Low bitrate falls apart the moment you grade it.
Artifacts are blocky and fixed; noise is grainy and random — denoising does nothing for artifacts.
Where to set it
On set: codec / compression ratio → how hard you can grade
On delivery: Deliver page → Render settings → Quality → how big the file is
On set: codec / compression ratio → how hard you can grade
On delivery: Deliver page → Render settings → Quality → how big the file is
same frame, same grade · bottom row at 200%
地基 3 / 3
采样 = 颜色可以少采
4:4:4（左）与 4:2:0（右）· 真片帧
JPEG 量化矩阵 · 低频保留，高频截断
4:2:0 = ½ × ½ = 1/4 色度信息。能播，不能抠——键控在色度上做判断，色度只剩四分之一，边缘的颜色是猜的。
那丢掉的去哪了？DCT 不丢，量化才丢，丢的是高频。高频系数被粗暴截断 → 块内细节失真、块间连续性断掉、边缘振铃——和傅里叶级数截断产生吉布斯现象是同一个数学原因。
同一个 4:2:0，视频里也是这个意思；量化的道理，图片和视频一样。
同一个 4:2:0，视频里也是这个意思；量化的道理，图片和视频一样。
Foundation 3 / 3
Chroma subsampling: colour can be sampled less
4:4:4 (left) vs 4:2:0 (right) · real frame
JPEG quantisation matrix · low kept, high cut
4:2:0 = ½ × ½ = a quarter of the chroma. It plays back, it does not key — the edge colours were interpolated guesses to begin with.
Where do the discarded bits go? The DCT loses nothing; quantisation is the only lossy step, and it takes the high frequencies. Truncating high-frequency coefficients distorts detail inside each block, breaks continuity between blocks and rings at edges — the same mathematics as Gibbs ringing in a truncated Fourier series.
The same 4:2:0 means the same thing in video; quantisation works the same way for stills and video alike.
The same 4:2:0 means the same thing in video; quantisation works the same way for stills and video alike.
概念 1 的补充 · 导览课讲过色域，这里补那条曲线
同一个数，两台设备两个亮度
Rec.709 传递函数 · Power function exponent 0.45 · Toe Slope 4.5
导览课讲过三角大小（709 < P3 < 2020）。这里补的是第三件：传递函数。同一个数值，在不同曲线上代表不同的亮度——709 用 0.45 幂，sRGB 是分段曲线，显示器实际按 BT.1886（γ≈2.4）。
这就是「同一个文件、两台设备、两种颜色」的另一半原因：要么三角不够大，要么曲线不一样。
视频系统通过对RGB信号施加 0.45 次幂变换，来模拟人眼的明度感知响应，这与 L* 定义的 1/3 次幂函数特性相近。 —— Charles Poynton
Filling in concept 1 · you had gamut in the orientation; here is the curve
Same number, two devices, two brightnesses
Rec.709 transfer function · power function exponent 0.45 · toe slope 4.5
The orientation covered triangle size (709 < P3 < 2020). What is new: the transfer function. The same number means a different brightness on a different curve — 709 uses a 0.45 power, sRGB is piecewise, and displays actually follow BT.1886 (γ≈2.4).
That is the other half of “one file, two devices, two colours”: either the triangle is too small, or the curve is different.
Video systems apply a 0.45 power to the RGB signal to mimic the eye’s lightness response, close to the 1/3 power in the L* definition. — Charles Poynton
概念 2 / 4 · 回扣烂画面 ②
Log 是打包方式
真片帧：原始信号（左，平）· 还原后（右，示意，非真 LUT）
灰不是坏了，是还没翻译。曝光是乘法、感知是对数，所以用对数存——ARRI LogC γ≈0.51，14 档动态范围要塞进 1024 级。
Concept 2 / 4 · back to ②
Log is a packing method
real frame: original (left, flat) · restored (right, schematic, not a real LUT)
Flat is not broken, it is untranslated. Exposure is multiplicative and perception is logarithmic — ARRI LogC γ≈0.51 packs 14 stops into 1024 levels.
概念 4 / 4 · 回扣烂画面 ④
噪点是信号的地板
光太弱，光子本身就忽多忽少（散粒噪声）
电路读数再叠一层误差（读出噪声）
电路读数再叠一层误差（读出噪声）
散粒噪声 ∝ √光子数：光少一半，信噪比掉 3 dB。暗部为什么脏，是算术问题。
前期没有光，就补光。
别指望相机设置帮你降噪。
别指望相机设置帮你降噪。
ISO、降噪、拉曲线，一个都不能真的增加光子。唯一治本的动作，是让更多光真的落到传感器上。
Concept 4 / 4 · back to ④
Noise is the floor of the signal
In low light, photons arrive unevenly (shot noise).
The circuitry adds its own error (read noise).
The circuitry adds its own error (read noise).
Shot noise ∝ √photons: halve the light and SNR drops 3 dB. Shadows are dirty by arithmetic.
No light? Add light.
Do not expect a camera setting to denoise for you.
Do not expect a camera setting to denoise for you.
ISO, noise reduction and curve-pulling cannot add a single photon. The only fix that works is more light actually reaching the sensor.
拍摄端的对策
向右曝光
不过曝的前提下，把画面往亮的那一侧推。高光贴着 95%，不撞顶。
把 ISO 调高
放大器增益变大 → 画面变亮
光子数没变，噪声一起放大
光子数没变，噪声一起放大
向右曝光
真的给更多光 → 光子数变多
信噪比真的提高（物理收益）
信噪比真的提高（物理收益）
所以推的是进光量，不是ISO 数字。混了这两件事，就会出现「我把 ISO 开高了，为什么还是脏」——因为你从来没给更多光。
噪点除不掉，只能让信号离它远一点。而唯一手段是加光。
EL Zone 色标 · 白色代表画面过曝6档及以上；18%灰色为标准中性曝光；黑色代表欠曝6档及以上。
怎么看见自己曝到哪一档：EL 分区把整帧按档上色，等于取景器里内置一支点测光表。注意：EL分区功能无法与LUT同时启用。
The on-set answer
Expose to the right
Short of clipping, push the image toward the bright side. Highlights around 95%, never on the ceiling.
Raise the ISO
More amplifier gain → brighter picture
Same photon count, noise amplified too
Same photon count, noise amplified too
Expose to the right
Actually more light → more photons
Real SNR gain, not a visual one
Real SNR gain, not a visual one
So you are pushing how much light gets in, not the ISO number. Mix the two and you get "I raised the ISO, why is it still noisy" — because you never gave it more light.
You cannot remove noise. You can only move the signal away from it. The only way is more light.
EL Zone chart · white means six stops over or more; 18% grey is standard neutral exposure; black means six stops under or more.
How you see which stop you are on: EL Zone colours the whole frame by stop — a spot meter built into the viewfinder. Note: EL Zone cannot be enabled at the same time as a LUT.