====== YUV 4:4:4 UVC Brightness ======

At this stage of the imaging pipeline the pixel data is represented in
full-range YCbCr 4:4:4 color space with 12-bit precision per component.

The purpose of this block is to apply **UVC Brightness adjustment** to the
image by modifying the luma component while preserving chroma.

===== Conceptual model =====
The UVC Brightness control is described in terms of an HSL-based model
in [[https://wiki.sub2r.com/doku.php/isp:brightness|UVC Brightness]]

Conceptually, UVC Brightness corresponds to a **uniform additive offset applied
to perceived lightness**.

In a YCbCr pipeline, this behavior maps directly to an **additive offset applied
to the luma (Y) component**, while chroma components remain unchanged.

This document specifies that mapping explicitly for FPGA implementation.

===== Input format =====
The input consists of YCbCr pixels with the following properties:

\[
 Y12 \in [0..4095]\\
 C_b12 \in [0..4095]\text{, neutral at }2048\\
 C_r12 \in [0..4095]\text{, neutral at }2048
\]

All values are unsigned 12-bit integers using full-range (computer-range)
coding.

===== Output format =====
The output format is identical to the input format:

\[
 Y12^{\text{bright}} \in [0..4095]\\
 C_b12^{\text{bright}} = C_b12\\
 C_r12^{\text{bright}} = C_r12
\]

Only the luma component is modified by the brightness stage.

===== Brightness offset definition =====
The UVC Brightness control provides a signed brightness offset value
\(B\), defined and scaled as specified in  [[https://wiki.sub2r.com/doku.php/isp:brightness|UVC Brightness]]

===== UVC Brightness implementation =====
Brightness is applied as a **signed additive offset** to the luma component:

\[
Y12^{\text{bright}} = clamp12(Y12 + B)
\]

Where:
  * \(Y12\) is the input luma value,
  * \(B\) is the signed brightness offset,
  * and `clamp12(x)` clamps the result to the range \([0..4095]\).

The chroma components are passed through unchanged:

\[
C_b12^{\text{bright}} = C_b12\\
C_r12^{\text{bright}} = C_r12
\]

===== FPGA implementation considerations =====
  * Brightness adjustment shall be implemented using **signed integer arithmetic**.
  * The addition must be performed at sufficient bit width to avoid overflow before clamping.
  * Clamping is applied **after** the addition.
  * No multiplications, divisions, or LUTs are required for this stage.

===== Notes =====
  * This block operates entirely in **YCbCr space**.
  * Brightness adjustment affects **only luma**, preserving chroma relationships.
  * The behavior is conceptually equivalent to the HSL-based UVC Brightness model.
  * This stage assumes **full-range (computer-range) YCbCr** coding.
  * Extreme brightness values may cause luma clipping, which is expected behavior.