opencode-image-resizer

OpenCode plugin that automatically resizes images over 5MB before sending to the Claude API.

Problem

Claude API has a 5MB limit per image. When you reference images in OpenCode (via @file or drag-and-drop), images exceeding this limit cause errors.

Solution

This plugin intercepts image reads and automatically resizes them using a ratio-based heuristic: it calculates how much the image needs to shrink and applies quality/resolution reduction in a single shot — no slow iterative scanning.

Install

Add to your opencode.json:

{
  "plugin": ["opencode-image-resizer"]
}

Configuration

Set via environment variables (e.g., in your shell profile or .env):

| Variable | Default | Description | |---|---|---| | IMAGE_RESIZER_MAX_SIZE_MB | 4.5 | Images above this size (MB) are resized. Max 5.0. | | IMAGE_RESIZER_MIN_QUALITY | 40 | Minimum JPEG quality (1–95). Plugin won't go below this. | | IMAGE_RESIZER_MIN_SCALE | 0.25 | Minimum resolution scale (0.1–1.0). 1.0 = never reduce resolution. |

# Example: higher quality, never reduce resolution
export IMAGE_RESIZER_MIN_QUALITY=65
export IMAGE_RESIZER_MIN_SCALE=1.0

How It Works

The plugin intercepts images at three points:

1. read tool (@file references): When the LLM reads an image file over the limit
2. chat.message: When you drag-and-drop an image into the terminal
3. resize_image tool: Explicit LLM-callable tool for manual resizing

Resize Strategy

Given ratio = originalSize / maxSize, parameters are determined in one shot:

| ratio | quality | scale | Example | |---|---|---|---| | ≤ 1.1x | 93 | 100% | 5.0MB → 4.5MB | | ≤ 1.3x | 88 | 100% | 5.5MB → 4.5MB | | ≤ 1.6x | 83 | 100% | 7MB → 4.5MB | | ≤ 2.0x | 78 | 100% | 9MB → 4.5MB | | ≤ 2.5x | 72 | 95% | 11MB → 4.5MB | | ≤ 3.5x | 66 | 88% | 15MB → 4.5MB | | ≤ 5.0x | 58 | 80% | 22MB → 4.5MB | | ≤ 8.0x | 50 | 70% | 36MB → 4.5MB | | ≤ 15x | 45 | 55% | — | | 15x+ | 40 | 40% | — |

If the first attempt misses (edge case), a safety retry applies -15 quality and 80% scale. Maximum 3 attempts total.

For lossless formats (PNG, BMP, TIFF): lossless PNG re-compression is tried first (zero quality loss), then JPEG conversion with the heuristic above.

Supported Formats

jpg, jpeg, png, gif, webp, bmp, tiff, tif, avif

GIF: only the first frame is used.

resize_image Tool

Ask Claude directly when needed:

이 이미지가 너무 크면 resize_image 도구로 줄여줘: /path/to/image.png

Supports the same options as the env config, overridable per-call:

| Arg | Type | Default | |---|---|---| | filePath | string | required | | maxSizeMB | number | IMAGE_RESIZER_MAX_SIZE_MB | | minQuality | number | IMAGE_RESIZER_MIN_QUALITY | | minScale | number | IMAGE_RESIZER_MIN_SCALE |

License

MIT