Sampling method - Euler A Ancestral

揭秘 AI 画师的调色盘：什么是 Euler A (Euler Ancestral) 采样方法？

在当今的人工智能艺术领域，尤其是像 Stable Diffusion 或 Midjourney 这样的工具中，你可能会在设置里看到一大堆神秘的选项，其中一个非常流行但名字听起来很像数学课本的词汇是：Euler A。

虽然它的全名 “Euler Ancestral” 听起来很高深，但别担心，我们不需要复习微积分就能理解它。今天，我们就用日常生活中的例子来揭开它的面纱。

1. 核心概念：AI 绘画其实就是“去噪”

要理解 Euler A，首先得知道 AI 是怎么画画的。现在的 AI 绘画模型（扩散模型）的工作原理并不是像人类画家那样一笔一画地从白纸开始。相反，它的工作方式更像是一个雕塑家或者是修复师。

  • 想象一下：
    如果给你一张全是雪花点的电视屏幕截图（全是杂乱的噪点），并告诉你：“这其实是一张可爱的小猫照片，只是被盖住了。” 你的任务是一点点擦去噪点，把小猫“找”回来。

AI 的绘画过程就是这样：它从一团完全随机的混沌（噪点）开始，一步步地预测“这下面应该有什么”，然后减去噪点，直到图像变得清晰。

这个一步步去除噪点、生成图像的过程，就叫做采样（Sampling）。而 Euler A 就是指导 AI 如何迈出这些步伐的一种特定策略。

2. 什么是 Euler A？

Euler（欧拉）指的是一种经典的数学方法，用来解决怎么从“现在的状态”推算出“下一步的状态”。而 A 代表 Ancestral（祖先的/祖传的），这就涉及到它独特的性格了。

为了理解 Euler A，我们把它和一个普通的老实人采样器（比如标准的 Euler）做个对比。

类比：在迷雾中寻找宝藏

想象一下，你站在一片浓雾弥漫的森林里（这就是那团噪点），你的任务是找到藏在某处的宝藏（最终的清晰画作）。

普通采样器 (如 Euler)：严格的导游

这种采样器就像是一个拿着死板地图的导游。它看了一眼指南针，说：“宝藏肯定在正北方。”然后它就会沿着这条直线坚定地走下去。每一步都严格遵循数学计算出的“最优解”。

  • 结果： 每次你站在同一个起点，它都会带你走完全相同的路，到达完全相同的终点。虽然稳定，但有时显得缺乏灵气。

Euler A 采样器：随性的且有直觉的探险家

Euler A 则不同。它是一个不仅看指南针，还会在此刻加入一点“随机性”（Random Noise）的探险家。
它会说：“指南针指向北方，但我觉得稍微偏西北一点点可能会有惊喜。”

  • 每一步的操作： 它在迈出一步清理噪点后，会再故意加回一点点新的噪点（这就是 “Ancestral” 的部分含义，它保留了一些随机性的“血统”）。
  • 结果： 即使起点完全一样，如果你让 Euler A 走两次，它每次迈出的步伐都会有微小的不同。这些微小的不同累积起来，最终的终点（画出的画）也会略有差异。

3. Euler A 的两大性格特征

对于使用者来说，Euler A 表现出两个非常显著的特点：

特征一：虽然不稳定，但充满惊喜（非收敛性）

很多采样器（如 LMS 或 DPM++）是“收敛”的。这意味着如果你给它们更多的时间（增加步数 Steps），画面细节会越来越精细，但画面构图基本定型不动。

Euler A 是不收敛的。

  • 比喻： 就像捏泥人。
    • 普通采样器：一旦确定了是捏一只狗，增加步数只是在不断打磨狗的毛发细节，狗的姿势不会变。
    • Euler A：随着步数增加，它可能会觉得“哎，这个狗腿也许可以抬起来”，“这只狗也许变成一只狼更酷”。哪怕在最后阶段，它也可能因为那一点点随机性，突然改变画面的构图或细节。

特征二：速度极快，构图柔和

Euler A 以运算速度快著称。它不需要极其复杂的计算就能在短短几步内（比如 20-30 步）生成一张非常好看的图。

而且，由于它在每一步都引入了微小的随机噪声，这就像在画画时不断地进行“柔化”处理。因此，Euler A 生成的图片通常具有：

  • 梦幻感
  • 结构多变
  • 边缘柔和

它不像某些硬核采样器那样追求极致的锐利度，但在创作创意插画、人像速写时，这种柔和感反而是一种优势。

4. 总结：什么时候该用 Euler A？

特性 Euler A 的表现 对日常使用的建议
创造力 ⭐⭐⭐⭐⭐ (极高) 当你没有特定的画面构图想法，想让 AI 给你一些意外惊喜时，选它！
稳定性 ⭐⭐ (较低) 如果你想微调一张图的一小部分细节，Euler A 可能会把整张图都改了，这时别用它。
速度 ⭐⭐⭐⭐⭐ (极快) 为了快速看效果、“抽卡”刷图，它是首选。
风格 柔和、梦幻、富有变化 适合二次元、概念艺术、梦境风格。

简单来说：

如果你是一个严格的建筑师，需要精准还原蓝图，请避开 Euler A。
如果你是一个寻找灵感的艺术家，希望在混沌中撞见奇迹，Euler A 就是你最好的缪斯。

Demystifying the AI Artist’s Palette: What is Euler A (Euler Ancestral)?

In the realm of Artificial Intelligence art, especially within tools like Stable Diffusion or Midjourney, you may encounter a bewildering array of settings. One of the most popular, yet mathematically formidable-sounding options, is Euler A.

Although its full name, “Euler Ancestral,” sounds sophisticated, fear not—we don’t need to revisit calculus to understand it. Today, we will unveil its mysteries using everyday analogies.

1. Core Concept: AI Art is Essentially “Denoising”

To understand Euler A, you first need to know how AI draws. Modern AI art models (Diffusion Models) don’t work like human painters, starting from a blank canvas and adding strokes. Instead, they work more like a sculptor or a restorer.

  • Imagine this:
    You are given a screenshot of a TV screen filled with static (pure, chaotic noise). You are told, “This is actually a photo of a cute cat, but it’s buried under the static.” Your task is to wipe away the noise bit by bit to “find” the cat.

This is the AI’s process: it starts from a blob of completely random chaos (noise) and step-by-step predicts “what should be underneath,” subtracting the noise until an image becomes clear.

This process of removing noise step-by-step to generate an image is called Sampling. And Euler A is simply a specific strategy guiding the AI on how to take those steps.

2. What is Euler A?

Euler refers to a classic mathematical method used to solve how to calculate the “next state” from the “current state.” The A stands for Ancestral, and this involves its unique personality.

To understand Euler A, let’s compare it with a standard, honest sampler (like the standard Euler).

Analogy: Hunting for Treasure in the Mist

Imagine you are standing in a thick, foggy forest (the noise), and your mission is to find treasure hidden somewhere (the final clear image).

Ordinary Sampler (e.g., Euler): The Strict Guide

This sampler operates like a guide holding a rigid map. It looks at the compass and says, “The treasure is definitely due North.” It then walks firmly in that straight line. Every step strictly follows the mathematically calculated “optimal path.”

  • Result: Every time you stand at the same starting point, it will take you down the exact same path to the exact same destination. It’s stable, but sometimes lacks flair.

Euler A Sampler: The Intuitive Explorer

Euler A is different. It is an explorer who checks the compass but also adds a bit of “randomness” (Random Noise) in the moment.
It might say, “The compass says North, but I feel like deviating slightly North-West might reveal a surprise.”

  • The Process: After taking a step to clean up some noise, it deliberately adds back a tiny bit of new noise. (This is part of what “Ancestral” implies; it keeps a “lineage” of randomness).
  • Result: Even if the starting point is exactly the same, if you let Euler A walk the path twice, its steps will differ slightly each time. These tiny differences accumulate, meaning the final destination (the generated image) will also vary slightly.

3. Two Key Personality Traits of Euler A

For the user, Euler A exhibits two very distinct characteristics:

Trait 1: Unstable, but Full of Surprises (Non-Convergent)

Many samplers (like LMS or DPM++) are “convergent.” This means if you give them more time (increase the Steps), the details of the image get finer, but the composition essentially “locks in.”

Euler A is non-convergent.

  • Metaphor: It’s like modeling clay.
    • Ordinary Sampler: Once it decides it’s making a dog, adding more steps just polishes the dog’s fur; the dog’s pose won’t change.
    • Euler A: As steps increase, it might decide, “Hey, maybe this dog’s leg should be lifted,” or “Maybe this dog would look cooler as a wolf.” Even in the final stages, that bit of added randomness allows it to suddenly shift the composition or details.

Trait 2: Extremely Fast with Soft Composition

Euler A is known for its speed. It creates very good-looking images in just a few steps (e.g., 20-30 steps) without needing incredibly complex calculations.

Moreover, because it introduces tiny amounts of random noise at every step, it acts like a constant “softening” filter during the painting process. As a result, Euler A images often possess:

  • A dreamlike quality
  • Variable structures
  • Softer edges

It doesn’t pursue the extreme sharpness of some hardcore samplers, but for creative illustrations and portraits, this softness acts as an advantage.

4. Summary: When Should You Use Euler A?

Feature Euler A Performance Advice for Daily Use
Creativity ⭐⭐⭐⭐⭐ (Very High) Choose this when you don’t have a specific composition in mind and want the AI to surprise you!
Stability ⭐⭐ (Low) If you want to fine-tune a small detail of an image, avoid this; Euler A might change the whole picture.
Speed ⭐⭐⭐⭐⭐ (Very Fast) It is the top choice for quickly testing prompts or “gacha” style image generation.
Style Soft, dreamlike, variable Great for Anime, Concept Art, and Dream styles.

In short:

If you are a strict architect needing to precisely replicate a blueprint, avoid Euler A.
If you are an artist seeking inspiration and hoping to stumble upon a miracle within the chaos, Euler A is your best muse.