--- name: codex-image-gen description: >- Generate raster images (icons, illustrations, textures, app icons) from a text prompt by driving the Codex CLI's image tool, then extracting the finished PNG from the Codex session rollout. Use when an agent needs a real generated image and has no native image-generation tool. Requires the `codex` CLI, logged in. license: MIT compatibility: Requires the `codex` CLI (logged in) plus `python3` and `base64`; `sips` is optional for post-processing on macOS. metadata: version: "1.0.0" tags: "codex, image-generation, gpt-image, cli, assets, app-icon" when_to_use: "generate an image, make an icon, create an app icon, render an illustration or texture, agent needs an image but has no image tool, codex image generation" ---

# Codex Image Gen

Generate a real raster image from a text prompt when the running agent has no native image generator. The mechanism is non-obvious: the headless `codex exec` path genuinely calls the image tool, but it never writes the PNG to disk — only the Codex desktop app has the plumbing that polls the async job and saves it. The finished image is still recoverable, because its full base64 PNG is recorded in the session rollout JSONL. Run the prompt, read the session id Codex prints, open the matching rollout, and decode the largest `result` string to a PNG.

## When this is the right tool

- The agent needs a generated raster image (icon, illustration, texture, app icon, placeholder art) and has no built-in image-generation tool. - A `codex` CLI is installed and logged in, and shelling out to it is allowed. - A vector result is **not** required — this produces a PNG, not an SVG.

If a native image tool exists, prefer it. If the deliverable is a logo or crisp vector, prefer a vector workflow.

## Why the naive approach fails

Running `codex exec "draw a ..."` and then watching `~/.codex/generated_images/` produces nothing: that folder is written by the desktop app's async-job poller, not by `codex exec`. People conclude CLI image generation is impossible. It is not — the completed image lives in the session rollout as the `result` field of the image-generation response item. This skill reads it from there.

## Pipeline

### 1. Write the prompt to a file

Avoid shell-escaping pain by putting the prompt in a file. Be explicit — the model has no other context:

- Subject and style ("flat vector mark", "glossy 3D glass icon", "hand-drawn"). - Composition: full-bleed vs. padded, centered, single object vs. scene. - Palette and background (solid color, transparent intent, gradient). - `NO text, NO letters, NO words` unless you specifically want type. - Target aspect ratio and rough size.

```bash cat > /tmp/img-prompt.txt <<'PROMPT' A single app icon: a glossy translucent envelope on a soft blue-to-violet gradient, Liquid Glass style, centered with even padding, no text, no letters, 1:1 square, high detail. PROMPT ```

### 2. Run `codex exec` and capture stdout

```bash codex exec -s read-only "$(cat /tmp/img-prompt.txt)" 2>&1 | tee /tmp/codex-run.log ```

Run it in the **foreground**. `exec` returns once the turn completes; in practice the `result` is already written to the rollout by then.

### 3. Parse the session id

Codex prints a `session id: <uuid>` line. Pull it from the captured log:

```bash SESSION_ID=$(grep -oE 'session id: [0-9a-f-]{36}' /tmp/codex-run.log | awk '{print $3}') echo "session: $SESSION_ID" ```

### 4. Extract the PNG from the rollout

The rollout lives at `~/.codex/sessions/YYYY/MM/DD/rollout-*<session-id>*.jsonl`. Walk it, find the largest `result` string (the base64 image), and decode it. Use the bundled helper:

```bash python3 scripts/extract-codex-image.py "$SESSION_ID" /tmp/out.png ```

### 5. Assert success

Confirm the file exists and is a real PNG before using it:

```bash test -s /tmp/out.png && file /tmp/out.png # expect: PNG image data, 1254 x 1254 ```

If extraction finds no base64 `result`, the turn did not actually generate an image (e.g. the model answered in text). Re-run step 2 with a more explicit "generate an image" instruction.

### 6. Post-process (optional)

Default output is roughly **1254×1254 PNG, RGB, no alpha**. Resize / strip alpha with `sips` on macOS:

```bash sips -z 1024 1024 /tmp/out.png --out /tmp/icon-1024.png # downscale sips -s format png /tmp/out.png --out /tmp/flat.png # normalize ```

## Reference extractor

`scripts/extract-codex-image.py` (also reproduced here so the procedure is self-contained):

```python import json, sys, base64, glob, os

session_id, out = sys.argv[1], sys.argv[2] sess = max( glob.glob(os.path.expanduser(f"~/.codex/sessions/**/*{session_id}*.jsonl"), recursive=True), key=os.path.getmtime, ) best = None

def walk(o): global best if isinstance(o, dict): for k, v in o.items(): if k == "result" and isinstance(v, str) and len(v) > 100000: if best is None or len(v) > len(best): best = v else: walk(v) elif isinstance(o, list): for v in o: walk(v)

for line in open(sess): try: walk(json.loads(line)) except Exception: pass

if best is None: sys.exit("no base64 image result found in rollout — the turn may not have generated an image") open(out, "wb").write(base64.b64decode(best)) print("WROTE", out) ```

## Worked example: build a macOS/iOS app icon set

```bash # 1. Generate a 1:1 icon master. cat > /tmp/icon-prompt.txt <<'PROMPT' App icon: a glossy translucent envelope, Liquid Glass style, soft blue-to-violet gradient background, centered, even padding, no text, no letters, 1:1 square. PROMPT codex exec -s read-only "$(cat /tmp/icon-prompt.txt)" 2>&1 | tee /tmp/codex-run.log SESSION_ID=$(grep -oE 'session id: [0-9a-f-]{36}' /tmp/codex-run.log | awk '{print $3}') python3 scripts/extract-codex-image.py "$SESSION_ID" /tmp/icon-master.png

# 2. Make a 1024 master with no alpha (iOS rejects alpha on the marketing icon). sips -z 1024 1024 /tmp/icon-master.png --out /tmp/AppIcon-1024.png sips -s format png --setProperty hasAlpha false /tmp/AppIcon-1024.png --out /tmp/AppIcon-1024.png

# 3. Slice into an AppIcon.appiconset (iOS single-size 1024 + the macOS ladder). mkdir -p AppIcon.appiconset cp /tmp/AppIcon-1024.png AppIcon.appiconset/icon_1024.png for sz in 16 32 64 128 256 512 1024; do sips -z "$sz" "$sz" /tmp/AppIcon-1024.png --out "AppIcon.appiconset/icon_${sz}.png" done # Author Contents.json mapping each size/scale to its file, then verify: # actool --compile /tmp/out --app-icon AppIcon --platform iphoneos \ # --minimum-deployment-target 17.0 AppIcon.appiconset # expect a clean compile ```

## Gotchas

- **The `codex` alias may inject `--dangerously-bypass-approvals-and-sandbox`**, which overrides any `-s read-only` you pass (the session then reports `danger-full-access`). Harmless for pure image generation, but worth knowing. Prefer running `codex exec` in the foreground — a backgrounded full-access run can trip auto-approval classifiers. - **Size and alpha.** Output is ~1254×1254, RGB, no alpha. Downscale to 1024 for an Apple icon master; iOS rejects alpha on the marketing icon. - **Async timing.** `exec` ends when the turn completes; the `result` is already in the rollout by then in practice. Still assert the file exists and decodes — do not assume. - **Fragility — pinned to `codex-cli 0.141.0`.** This depends on a Codex CLI internal: the rollout `result` field. A future Codex may change the rollout schema or add a first-class `--save-image` / output-path flag. If such a flag exists, prefer it and keep this rollout-extraction path as the fallback. If the extractor finds no base64 `result`, first check whether the rollout layout changed under `~/.codex/sessions/`.