--- title: "How to add a pencil sketch with Claude (tested prompt and script)" description: "At one second the purple and the holographic shimmer vanish, leaving the bottle traced in soft gray pencil on near-white paper, with the dropper cap shaded darkest and faint strokes where the backdrop's folds were. Install one skill and ask Claude Code, or run the Python script we tested yourself." url: https://www.recharm.com/effects/pencil-sketch --- # How to add a pencil sketch with Claude At one second the purple and the holographic shimmer vanish, leaving the bottle traced in soft gray pencil on near-white paper, with the dropper cap shaded darkest and faint strokes where the backdrop's folds were. Made by the script on this page, from our own test clip. ## Get this effect 1. ### Switch to Code in your [Claude Desktop App](https://claude.com/download) 2. ### Install the skill (once) ``` Install the Recharm video effects skill: download https://recharm-growth-staging.s3.us-east-2.amazonaws.com/website/downloads/recharm-video-effects.zip and unzip it into ~/.claude/skills ``` 3. ### Ask for the effect ``` Add a pencil sketch to input.mp4 Second the picture turns into a pencil drawing: 1.0 Blur radius in pixels for the dodge blend: 12 ``` ## Several videos, several effects, one ask Put your clips in the folder, mention them with @, and ask for everything at once. Claude runs one tested script after another on each clip, then joins them. Add a pencil sketch to **@clip1.mp4**, put a sale badge on **@clip2.mp4**, give **@clip3.mp4** a VHS look, then join all three with crossfades. ## Settings you can change Ask Claude to change any of these, or edit them at the top of the script. | Setting | Default | What it does | | -------- | ----------------- | ----------------------------------------------------------------------------------------------------------------- | | `START` | `1.0` | Second the picture turns into a pencil drawing. | | `BLUR` | `12` | Blur radius in pixels for the dodge blend. Bigger draws bolder, softer strokes; smaller gives thin outlines only. | | `DARKEN` | `2.6` | Power applied to the sketch. Higher makes the lines and shading darker; 1 leaves them faint. | | `PAPER` | `(250, 250, 247)` | Paper color. | | `GRAIN` | `6` | Paper grain strength (0-255). 0 gives perfectly smooth paper. | ## Without the skill Don’t want to install the skill? Paste this prompt into Claude Code and Claude writes the script itself. ``` Turn input.mp4 (540x960) into a gray pencil sketch from 1.0 seconds to the end; before 1.0 seconds leave it untouched. Use Python with OpenCV and numpy. For each frame from 1.0 s: convert it to grayscale, invert it, Gaussian-blur the inverted image with sigma 12 pixels, and color-dodge the grayscale over it (cv2.divide(gray, 255 - blurred_inverted, scale=256)). Scale the result to 0-1, raise it to the power 2.6 to darken the strokes, multiply it by a fixed paper grain (1 minus random noise blurred with sigma 0.8, at most 6/255, the same for every frame) and multiply by the paper color (250, 250, 247), so bare paper is (250, 250, 247) and the strokes are neutral gray with no color left. Read and write frames through ffmpeg (don't use ffmpeg's drawtext if you add any text), keep the size, 30fps, the 6 second length and the audio, and save it as output.mp4. ``` ## Run it without Claude This is the exact script we tested. Save it as `pencil-sketch.py` and run: ``` python3 pencil-sketch.py input.mp4 output.mp4 ``` ``` #!/usr/bin/env python3 """Pencil sketch: at one second the colors drop away and the shot is redrawn as gray pencil lines and shading on white paper. Usage: python3 pencil-sketch.py input.mp4 output.mp4 Needs ffmpeg, numpy and OpenCV for the blur and dodge blend (pip install numpy opencv-python-headless). """ import json import subprocess import sys import cv2 import numpy as np START = 1.0 # second the picture turns into a pencil drawing BLUR = 12 # blur radius in pixels for the dodge blend; bigger draws bolder, softer strokes DARKEN = 2.6 # power applied to the sketch; higher makes the lines and shading darker PAPER = (250, 250, 247) # paper color GRAIN = 6 # paper grain strength (0-255); 0 gives perfectly smooth paper def sketch(img): """Redraw one frame (h, w, 3, RGB) as pencil: a color-dodge of the grayscale over its own blurred negative.""" gray = cv2.cvtColor(img, cv2.COLOR_RGB2GRAY) blurred_negative = cv2.GaussianBlur(255 - gray, (0, 0), BLUR) lines = cv2.divide(gray, 255 - blurred_negative, scale=256).astype(np.float32) / 255 # 1 = bare paper lines = np.clip(lines, 0, 1) ** DARKEN lines = lines * (1 - grain) # graphite skips over the paper's tooth return (lines[..., None] * paper).astype(np.uint8) def probe(path): info = json.loads(subprocess.check_output(["ffprobe", "-v", "error", "-select_streams", "v:0", "-show_entries", "stream=width,height,r_frame_rate", "-of", "json", path])) s = info["streams"][0] num, den = s["r_frame_rate"].split("/") return s["width"], s["height"], s["r_frame_rate"], float(num) / float(den) src, out = sys.argv[1:3] w, h, rate, fps = probe(src) paper = np.array(PAPER, np.float32) grain = cv2.GaussianBlur(np.random.default_rng(1).random((h, w), np.float32), (0, 0), 0.8) * GRAIN / 255 reader = subprocess.Popen(["ffmpeg", "-v", "error", "-i", src, "-f", "rawvideo", "-pix_fmt", "rgb24", "-"], stdout=subprocess.PIPE) writer = subprocess.Popen(["ffmpeg", "-y", "-v", "error", "-f", "rawvideo", "-pix_fmt", "rgb24", "-s", f"{w}x{h}", "-r", rate, "-i", "-", "-i", src, "-map", "0:v", "-map", "1:a?", "-c:v", "libx264", "-crf", "18", "-pix_fmt", "yuv420p", "-c:a", "copy", "-shortest", out], stdin=subprocess.PIPE) i = 0 while raw := reader.stdout.read(w * h * 3): img = np.frombuffer(raw, np.uint8).reshape(h, w, 3) if i / fps >= START: img = sketch(img) writer.stdin.write(img.tobytes()) i += 1 writer.stdin.close() if reader.wait() or writer.wait(): sys.exit("ffmpeg failed") ``` ## More stylize and art - [Anime style **Anime style**](https://www.recharm.com/effects/anime-style) - [ASCII art **ASCII art**](https://www.recharm.com/effects/ascii-art) - [Blueprint **Blueprint**](https://www.recharm.com/effects/blueprint) - [Charcoal drawing **Charcoal drawing**](https://www.recharm.com/effects/charcoal-drawing) - [Claymation style **Claymation style**](https://www.recharm.com/effects/claymation-style) ## Find 3x _winning ads_ Recharm cuts your ad footage into tagged, searchable clips: hooks, testimonials, product shots. Find the shots that win, add the effect with Claude, and ship 3x more ad edits. [Start 14-day free trial](https://www.recharm.com/get-started)