resize-for-banner

Rescale an image (usually a screenshot from imgs/) into social banner versions: 16:9 for the LinkedIn article header and 5:2 for Twitter/X, using ImageMagick. The image is resized to fit and the leftover space is padded black — never cropped. Use when the user wants a banner, cover photo, or "16:9 / 5:2" version for a social profile or article header. Never overwrites the original — creates new files beside it.

Resize for Banner (LinkedIn / Twitter)

Turn one image into social banner variants with ImageMagick, keeping the original file untouched and writing new files beside it. The image is rescaled to fit and black-padded, never cropped, so no content is lost.

Platform specs

• LinkedIn article — 16:9 ratio, 1200x675 px (article header image).
• Twitter / X — 5:2 ratio, 1500x600 px (header photo).
• If two requested ratios are identical there is no reason to make both; otherwise produce one per distinct size.
• 16:9 and 5:2 differ, so normally two files are produced.

Approval gate

• Never touch the original image. All output goes to new files named after the original (suffix added, base name unchanged).
• Confirm the plan with the user before converting: the source image, the target size(s), and the exact output filenames.
• If the user asks for a size the spec does not cover (e.g. 1500x600 / 5:2), use that size with the same resize + pad technique and say which platform it suits.

Inputs

• source — Path to the original image, e.g. ai-thoughts/imgs/260806-1656.png. Required.
• sizes — Which banners to produce. Default: LinkedIn article 1200x675 and Twitter 1500x600.

Outputs

• imgs/<base>-banner-linkedin.png — 1200x675 (16:9 article), aspect preserved, black padding.
• imgs/<base>-banner-twitter.png — 1500x600 (5:2), aspect preserved, black padding.
• <base> keeps the original filename exactly (e.g. 260806-1656 → 260806-1656-banner-linkedin.png). The original file is never modified.

Procedure

1. Confirm the plan with the user: source image, target sizes, output filenames. Get a go-ahead before writing files.

2. Check the original dimensions with identify or magick identify "<source>" so you can predict which axis will be padded.

3. Resize to fit, then pad with black with ImageMagick 7 magick:

   sh

   # LinkedIn article — fit inside 1200x675, center on black 1200x675 canvas
   magick <source> -resize "1200x675" -background black -gravity center \
     -extent 1200x675 imgs/<base>-banner-linkedin.png
   
   # Twitter — fit inside 1500x600, center on black 1500x600 canvas
   magick <source> -resize "1500x600" -background black -gravity center \
     -extent 1500x600 imgs/<base>-banner-twitter.png
   

   • -resize "WxH" (no bang) scales to fit inside the box, preserving the aspect ratio — the image is never distorted or cropped.
   • -extent WxH then pads the leftover space; -background black makes the padding dark and -gravity center centers the image.
   • If the source is taller/narrower than the target ratio, padding appears on the left and right; if it is wider, padding appears on top and bottom.
   • Padding color is black by default; ask the user if they want a different background.

4. Verify every output with identify — dimensions must match the target size exactly.

5. Report the output paths and confirm the original is untouched (git status shows the new files as untracked, the original unmodified).

Quality rules

• Never overwrite or rename the source image.
• Never crop the image. Resize to fit and pad — cropping loses content.
• Do not invent dimensions: LinkedIn article = 1200x675, Twitter = 1500x600.

Verification

• identify reports exactly 1200x675 and 1500x600 for the two outputs.
• The source image inside the banner is undistorted (aspect ratio preserved).
• The original file is byte-identical (unchanged identify output / git status).
• Output files sit beside the original in the same directory.

Error Handling

• Source not found: list candidate images in imgs/ and ask which to use.
• Output already exists: stop and ask whether to overwrite, or choose a different suffix.
• User wants one image for both platforms: explain that 16:9 and 5:2 differ, so a single image cannot satisfy both exact specs; offer to make both, or a single compromise size if the user insists.
• No ImageMagick: magick is always installed on the user's machines — skip checking for it and run the commands directly.