docs: readme image section

packages/ai/README.md

@@ -16,6 +16,10 @@ Unified LLM API with automatic model discovery, provider configuration, token an
   - [Validating Tool Arguments](#validating-tool-arguments)
   - [Complete Event Reference](#complete-event-reference)
 - [Image Input](#image-input)
+- [Image Generation](#image-generation)
+  - [Basic Image Generation](#basic-image-generation)
+  - [Streaming Image Events](#streaming-image-events)
+  - [Notes and Limitations](#notes-and-limitations)
 - [Thinking/Reasoning](#thinkingreasoning)
   - [Unified Interface](#unified-interface-streamsimplecompletesimple)
   - [Provider-Specific Options](#provider-specific-options-streamcomplete)
@@ -419,6 +423,117 @@ for (const block of response.content) {
 }
 ```
 
+## Image Generation
+
+Image generation uses a separate API surface from text/chat generation. Use `getImageModel()` / `getImageModels()` / `getImageProviders()` to discover image-generation models, `images()` to stream events, and `generateImages()` to get the final result.
+
+Do not use `stream()` or `complete()` for image generation. Request options, error handling, and event/result flow follow the same overall pattern as the streaming APIs, but use image-specific types and events.
+
+### Basic Image Generation
+
+```typescript
+import { getImageModel, generateImages } from '@mariozechner/pi-ai';
+
+const model = getImageModel('openrouter', 'google/gemini-2.5-flash-image');
+
+const result = await generateImages(model, {
+  input: [{ type: 'text', text: 'Generate a red circle on a plain white background.' }]
+}, {
+  apiKey: process.env.OPENROUTER_API_KEY
+});
+
+for (const block of result.output) {
+  if (block.type === 'text') {
+    console.log(block.text);
+  } else if (block.type === 'image') {
+    console.log(block.mimeType);
+    console.log(block.data.substring(0, 32));
+  }
+}
+```
+
+Some models also support image input:
+
+```typescript
+import { readFileSync } from 'fs';
+
+const imageBuffer = readFileSync('input.png');
+const result = await generateImages(model, {
+  input: [
+    { type: 'text', text: 'Create a variation of this image with a blue background.' },
+    { type: 'image', data: imageBuffer.toString('base64'), mimeType: 'image/png' }
+  ]
+}, {
+  apiKey: process.env.OPENROUTER_API_KEY
+});
+```
+
+Check capabilities on the model metadata:
+
+```typescript
+console.log(model.input);   // ['text', 'image']
+console.log(model.output);  // ['image'] or ['image', 'text']
+```
+
+### Streaming Image Events
+
+`images()` returns an `AssistantImagesEventStream` with image-specific events:
+
+```typescript
+import { getImageModel, images } from '@mariozechner/pi-ai';
+
+const model = getImageModel('openrouter', 'google/gemini-2.5-flash-image');
+const s = images(model, {
+  input: [{ type: 'text', text: 'Generate a simple green triangle.' }]
+}, {
+  apiKey: process.env.OPENROUTER_API_KEY
+});
+
+for await (const event of s) {
+  switch (event.type) {
+    case 'start':
+      console.log(`Starting image generation with ${event.partial.model}`);
+      break;
+    case 'image_start':
+      console.log(`Image block started at index ${event.contentIndex}`);
+      break;
+    case 'image_end':
+      console.log(`Image block complete: ${event.image.mimeType}`);
+      break;
+    case 'done':
+      console.log(`Finished: ${event.reason}`);
+      break;
+    case 'error':
+      console.error(`Error: ${event.error.errorMessage}`);
+      break;
+  }
+}
+
+const finalResult = await s.result();
+```
+
+| Event Type | Description | Key Properties |
+|------------|-------------|----------------|
+| `start` | Stream begins | `partial`: Initial `AssistantImages` structure |
+| `image_start` | Image block starts | `contentIndex`: Position in output array |
+| `image_end` | Image block complete | `image`: Final `ImageContent`, `contentIndex`: Position |
+| `done` | Stream complete | `reason`: Stop reason (`"stop"`), `images`: Final `AssistantImages` |
+| `error` | Error occurred | `reason`: Error type (`"error"` or `"aborted"`), `error`: Final `AssistantImages` |
+
+Text output, if the model returns any, is available on the final `AssistantImages.output` array.
+
+### Notes and Limitations
+
+- Use `getImageModel(...)`, not `getModel(...)`.
+- Use `images()` / `generateImages()`, not `stream()` / `complete()`.
+- Image-generation models do not participate in tool calling.
+- Outputs are returned as base64-encoded `ImageContent` blocks in `AssistantImages.output`.
+- Some models return only images, others return images plus text. Check `model.output`.
+- Some models accept image input, others are text-to-image only. Check `model.input`.
+- Like the streaming APIs, image generation supports options such as `apiKey`, `signal`, `headers`, `onPayload`, and `onResponse`, and results may include `stopReason`, `responseId`, and `usage`.
+- If you want a model to analyze images in a conversation or call tools, use the regular `stream()` / `complete()` APIs with a model that supports image input.
+- At the moment, image generation is available through only one provider, OpenRouter.
+
 ## Thinking/Reasoning
 
 Many models support thinking/reasoning capabilities where they can show their internal thought process. You can check if a model supports reasoning via the `reasoning` property. If you pass reasoning options to a non-reasoning model, they are silently ignored.