diff --git a/libsquoosh/src/codecs.ts b/libsquoosh/src/codecs.ts
index 98052cd6..c0410221 100644
--- a/libsquoosh/src/codecs.ts
+++ b/libsquoosh/src/codecs.ts
@@ -29,14 +29,23 @@ interface ResizeWithAspectParams {
   target_height: number;
 }
 
-interface ResizeInstantiateOptions {
+export interface ResizeOptions {
   width: number;
   height: number;
-  method: string;
+  method: 'triange' | 'catrom' | 'mitchell' | 'lanczos3';
   premultiply: boolean;
   linearRGB: boolean;
 }
 
+export interface QuantOptions {
+  numColors: number;
+  dither: number;
+}
+
+export interface RotateOptions {
+  numRotations: number;
+}
+
 declare global {
   // Needed for being able to use ImageData as type in codec types
   type ImageData = import('./image_data.js').default;
@@ -171,13 +180,7 @@ export const preprocessors = {
         buffer: Uint8Array,
         input_width: number,
         input_height: number,
-        {
-          width,
-          height,
-          method,
-          premultiply,
-          linearRGB,
-        }: ResizeInstantiateOptions,
+        { width, height, method, premultiply, linearRGB }: ResizeOptions,
       ) => {
         ({ width, height } = resizeWithAspect({
           input_width,
@@ -218,7 +221,7 @@ export const preprocessors = {
         buffer: Uint8Array,
         width: number,
         height: number,
-        { numColors, dither }: { numColors: number; dither: number },
+        { numColors, dither }: QuantOptions,
       ) =>
         new ImageData(
           imageQuant.quantize(buffer, width, height, numColors, dither),
@@ -239,7 +242,7 @@ export const preprocessors = {
         buffer: Uint8Array,
         width: number,
         height: number,
-        { numRotations }: { numRotations: number },
+        { numRotations }: RotateOptions,
       ) => {
         const degrees = (numRotations * 90) % 360;
         const sameDimensions = degrees == 0 || degrees == 180;
diff --git a/libsquoosh/src/index.ts b/libsquoosh/src/index.ts
index 48c15091..8a8880e8 100644
--- a/libsquoosh/src/index.ts
+++ b/libsquoosh/src/index.ts
@@ -2,7 +2,13 @@ import { isMainThread } from 'worker_threads';
 import { cpus } from 'os';
 import { promises as fsp } from 'fs';
 
-import { codecs as encoders, preprocessors } from './codecs.js';
+import {
+  codecs as encoders,
+  preprocessors,
+  QuantOptions,
+  ResizeOptions,
+  RotateOptions,
+} from './codecs.js';
 import WorkerPool from './worker_pool.js';
 import { autoOptimize } from './auto-optimizer.js';
 import type ImageData from './image_data';
@@ -12,6 +18,12 @@ type EncoderKey = keyof typeof encoders;
 type PreprocessorKey = keyof typeof preprocessors;
 type FileLike = Buffer | ArrayBuffer | string | ArrayBufferView;
 
+type PreprocessOptions = {
+  resize?: ResizeOptions;
+  quant?: QuantOptions;
+  rotate?: RotateOptions;
+};
+
 async function decodeFile({
   file,
 }: {
@@ -183,10 +195,10 @@ class Image {
 
   /**
    * Define one or several preprocessors to use on the image.
-   * @param {object} preprocessOptions - An object with preprocessors to use, and their settings.
+   * @param {PreprocessOptions} preprocessOptions - An object with preprocessors to use, and their settings.
    * @returns {Promise<undefined>} - A promise that resolves when all preprocessors have completed their work.
    */
-  async preprocess(preprocessOptions = {}) {
+  async preprocess(preprocessOptions: PreprocessOptions = {}) {
     for (const [name, options] of Object.entries(preprocessOptions)) {
       if (!Object.keys(preprocessors).includes(name)) {
         throw Error(`Invalid preprocessor "${name}"`);