diff --git a/js/image-viewer/transform.ts b/js/image-viewer/transform.ts
new file mode 100644
index 0000000000..afee7fe4a6
--- /dev/null
+++ b/js/image-viewer/transform.ts
@@ -0,0 +1,137 @@
+import { positiveAdd, positiveSubtract } from '../input-number/number';
+import type { ZoomOptions, ZoomResult, TranslateOffset, ImageScale } from './types';
+
+export type { ZoomOptions, ZoomResult, TranslateOffset, ImageScale };
+
+/** ImageScale 的默认值，所有使用处应引用此常量，避免多处声明不一致 */
+export const DEFAULT_IMAGE_SCALE: ImageScale = {
+  max: 2,
+  min: 0.5,
+  step: 0.2,
+  defaultScale: 1,
+};
+
+/**
+ * 检测图片是否超出视口（容器）边界
+ * @param container 外层容器元素
+ * @param modalBox 图片包裹元素
+ */
+export const isImageExceedsViewport = (container: HTMLElement, modalBox: HTMLElement): boolean => {
+  const containerRect = container.getBoundingClientRect();
+  const modalRect = modalBox.getBoundingClientRect();
+  return (
+    modalRect.left < containerRect.left ||
+    modalRect.right > containerRect.right ||
+    modalRect.top < containerRect.top ||
+    modalRect.bottom > containerRect.bottom
+  );
+};
+
+/** 镜像默认值（未镜像） */
+export const MIRROR_DEFAULT = 1;
+
+/** 切换镜像状态：1 → -1，-1 → 1 */
+export const toggleMirror = (current: number): number => (current > 0 ? -1 : 1);
+
+/** 每次旋转的角度（逆时针 90°） */
+export const ROTATE_DEG = -90;
+
+/**
+ * 计算最短路径归零的旋转补偿值
+ * 用于 resetRotate 场景：避免 CSS transition 时图片"倒转一大圈"
+ *
+ * @param currentDeg 当前累计旋转角度
+ * @returns 需要减去的补偿值（rotate.value -= 返回值 即可归零）
+ *
+ * @example
+ * // currentDeg = -270 → return 90（-270 - 90 = -360 ≡ 0°）
+ * // currentDeg = -180 → return -180（-180 - (-180) = 0）
+ * // currentDeg = 0 → return 0（无需旋转）
+ */
+export function calcResetRotation(currentDeg: number): number {
+  const degreeToRotate = currentDeg % 360;
+  if (degreeToRotate === 0) return 0;
+  // 找最短方向旋转回 0°
+  return Math.abs(degreeToRotate) > 180 ? (degreeToRotate + 360) % 360 : degreeToRotate;
+}
+
+/** 将缩放值限制在 [min, max] 范围内 */
+export function clampScale(value: number, min: number, max: number): number {
+  return Math.max(min, Math.min(max, value));
+}
+
+/**
+ * 计算放大后的新 scale 值（使用精确浮点数加法）
+ * @returns clamp 后的新 scale 值
+ */
+export function calcZoomInScale(oldScale: number, step: number, min: number, max: number): number {
+  return clampScale(positiveAdd(oldScale, step), min, max);
+}
+
+/**
+ * 计算缩小后的新 scale 值（使用精确浮点数减法）
+ * @returns clamp 后的新 scale 值
+ */
+export function calcZoomOutScale(oldScale: number, step: number, min: number, max: number): number {
+  return clampScale(positiveSubtract(oldScale, step), min, max);
+}
+
+/**
+ * 计算缩放后的位移补偿
+ * 公式：newTranslate = scaleRatio * T + (1 - scaleRatio) * Z
+ * 其中 Z 为缩放中心，T 为当前位移，scaleRatio = newScale / oldScale
+ */
+export function calculateTranslateOffset(
+  oldScale: number,
+  newScale: number,
+  options?: ZoomOptions
+): TranslateOffset | undefined {
+  if (options?.mouseOffsetX == null || options?.mouseOffsetY == null) {
+    return undefined;
+  }
+
+  const scaleRatio = newScale / oldScale;
+  const { translateX = 0, translateY = 0 } = options?.currentTranslate ?? {};
+  const { mouseOffsetX, mouseOffsetY } = options;
+
+  return {
+    translateX: scaleRatio * translateX + (1 - scaleRatio) * mouseOffsetX,
+    translateY: scaleRatio * translateY + (1 - scaleRatio) * mouseOffsetY,
+  };
+}
+
+/**
+ * 执行一次 zoom in 并计算位移补偿
+ * @returns { newScale, zoomResult }
+ */
+export function zoomIn(
+  oldScale: number,
+  step: number,
+  min: number,
+  max: number,
+  options?: ZoomOptions
+): { newScale: number; zoomResult: ZoomResult } {
+  const newScale = calcZoomInScale(oldScale, step, min, max);
+  return {
+    newScale,
+    zoomResult: { newTranslate: calculateTranslateOffset(oldScale, newScale, options) },
+  };
+}
+
+/**
+ * 执行一次 zoom out 并计算位移补偿
+ * @returns { newScale, zoomResult }
+ */
+export function zoomOut(
+  oldScale: number,
+  step: number,
+  min: number,
+  max: number,
+  options?: ZoomOptions
+): { newScale: number; zoomResult: ZoomResult } {
+  const newScale = calcZoomOutScale(oldScale, step, min, max);
+  return {
+    newScale,
+    zoomResult: { newTranslate: calculateTranslateOffset(oldScale, newScale, options) },
+  };
+}
diff --git a/js/image-viewer/types.d.ts b/js/image-viewer/types.d.ts
deleted file mode 100644
index daef641437..0000000000
--- a/js/image-viewer/types.d.ts
+++ /dev/null
@@ -1,8 +0,0 @@
-export interface ImageInfo {
-  mainImage: string | File;
-  thumbnail?: string | File;
-  download?: boolean;
-  isSvg?: boolean;
-}
-
-export type Images = Array<string | File | ImageInfo>;
diff --git a/js/image-viewer/types.ts b/js/image-viewer/types.ts
new file mode 100644
index 0000000000..f8a77f473e
--- /dev/null
+++ b/js/image-viewer/types.ts
@@ -0,0 +1,42 @@
+export interface ImageInfo {
+  mainImage: string | File;
+  thumbnail?: string | File;
+  download?: boolean;
+  isSvg?: boolean;
+}
+
+export type Images = Array<string | File | ImageInfo>;
+
+/** 位移偏移量 */
+export interface TranslateOffset {
+  translateX: number;
+  translateY: number;
+}
+
+/** 缩放选项 */
+export interface ZoomOptions {
+  /** 缩放中心点 X 坐标（相对于预览图片容器中心的偏移量） */
+  mouseOffsetX?: number;
+  /** 缩放中心点 Y 坐标（相对于预览图片容器中心的偏移量） */
+  mouseOffsetY?: number;
+  /** 当前位移 */
+  currentTranslate?: TranslateOffset;
+}
+
+/** 缩放结果 */
+export interface ZoomResult {
+  /** 缩放后的新位移 */
+  newTranslate?: TranslateOffset;
+}
+
+/** 图片缩放配置 */
+export interface ImageScale {
+  /** 缩放的最大比例 */
+  max: number;
+  /** 缩放的最小比例 */
+  min: number;
+  /** 缩放的步长速度 */
+  step: number;
+  /** 默认的缩放比例 */
+  defaultScale: number;
+}