asc screenshot resize

Use this skill to resize screenshots to the exact pixel dimensions required by App Store Connect and validate they pass upload requirements. Uses the built-in macOS sips tool — no third-party dependencies needed.

Required Dimensions

iPhone

Note: 6.9" accepts screenshots from 6.5", 6.7", and 6.9" devices. 6.3" accepts from 6.1" and 6.3". 6.1" accepts from 5.4", 5.8", and 6.1".

iPad

Apple Watch

Mac

Apple TV

Workflow

1. Fix Unicode filenames

macOS screenshots often contain hidden Unicode characters (e.g., U+202F narrow no-break space) that cause sips and other tools to fail with "not a valid file". Always sanitize first:

python3 -c "
import os
for f in os.listdir('.'):
    clean = f.replace('\u202f', ' ')
    if f != clean:
        os.rename(f, clean)
        print(f'Renamed: {clean}')
"

2. Check current dimensions

sips -g pixelWidth -g pixelHeight screenshot.png

3. Validate App Store readiness

Check for alpha channel and color space issues before uploading:

sips -g hasAlpha -g space screenshot.png

App Store Connect rejects screenshots with alpha transparency. Remove it by round-tripping through JPEG:

sips -s format jpeg input.png --out /tmp/temp.jpg
sips -s format png /tmp/temp.jpg --out output.png
rm /tmp/temp.jpg

Batch-strip alpha from all PNGs in a directory:

for f in *.png; do
  if sips -g hasAlpha "$f" | grep -q "yes"; then
    sips -s format jpeg "$f" --out /tmp/temp.jpg
    sips -s format png /tmp/temp.jpg --out "$f"
    rm /tmp/temp.jpg
    echo "Stripped alpha: $f"
  fi
done

4. Resize a single screenshot

# Portrait iPhone 6.5" (1284 × 2778)
sips -z 2778 1284 input.png --out output.png

Note: sips -z takes height first, then width: sips -z <height> <width>.

5. Batch resize all screenshots in a directory

mkdir -p resized
for f in *.png; do
  sips -z 2778 1284 "$f" --out "resized/$f"
done

6. Generate multiple device sizes from one source

mkdir -p appstore-screenshots
# iPhone
sips -z 2868 1320 input.png --out appstore-screenshots/iphone-6.9.png
sips -z 2778 1284 input.png --out appstore-screenshots/iphone-6.5.png
sips -z 2622 1206 input.png --out appstore-screenshots/iphone-6.3.png
sips -z 2532 1170 input.png --out appstore-screenshots/iphone-6.1.png
sips -z 2208 1242 input.png --out appstore-screenshots/iphone-5.5.png

7. Verify output

sips -g pixelWidth -g pixelHeight -g hasAlpha resized/*.png

Confirm all files show the target dimensions and hasAlpha: no.

Guardrails

• sips stretches images to fit exact dimensions. For best results, use source screenshots captured at or near the target aspect ratio.
• Always output to a separate file or directory (--out) to preserve originals.
• App Store Connect requires PNG or JPEG format. sips preserves the input format by default.
• Screenshots must not include alpha transparency. Always validate with sips -g hasAlpha before upload.
• Color space must be sRGB. If screenshots use Display P3, convert with: sips -m "/System/Library/ColorSync/Profiles/sRGB IEC61966-2.1.icc" input.png --out output.png.