ImageMagick is the standard free tool for batch resizing from the command line, and one magick mogrify line can shrink a whole folder. Its main trap is that mogrify overwrites the original files unless you tell it otherwise. If you want the same result without learning geometry syntax or risking your originals, OpticBatch from Automata Labs is a Windows app that resizes and converts JPEG, PNG and WebP folders by drag and drop, with Max Width, Max Height, Percentage or Exact sizing, a quality slider with a size estimate, and atomic writes so originals are never overwritten.
Drop a folder, choose a size and quality, and get resized copies without touching the originals.
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How do I batch resize images with ImageMagick?
ImageMagick is free and open source, and runs on Windows, macOS and Linux. Its license page listed version 7.1.2-34 when we checked. Batch work usually goes through magick mogrify. The mogrify documentation gives this example to resize every JPEG in a folder to fit within 256 by 256 pixels:
magick mogrify -resize 256x256 *.jpgAnd this one to convert every PNG in a folder to JPEG:
magick mogrify -format jpg *.pngThe documentation’s warning is the important part: mogrify is like magick “except that the original image file is overwritten (unless you change the file suffix with the -format option).” The first command above replaces your JPEGs with the smaller versions. The second leaves the PNG files untouched and creates new JPEG files beside them.
How do I resize with ImageMagick without overwriting originals?
Use the -path option, which mogrify’s option list describes as “write images to this path on disk.” Create an output folder first, then point mogrify at it:
mkdir resized
magick mogrify -path resized -resize "1600x1600>" -quality 82 *.jpgThat command:
- writes the results into
resizedand leaves the originals alone, - fits each image within 1600 by 1600 pixels,
- only shrinks images that are larger, thanks to the
>, - saves the JPEGs at quality 82.
On Windows, keep the geometry in double quotes. The > character means output redirection in the Command Prompt, and without quotes the command does something you did not intend.
What do ImageMagick’s geometry options mean?
The command-line processing guide lists the geometry modifiers:
| Geometry | What it does |
|---|---|
50% | Scales width and height by the percentage |
1600x1600 | Maximum width and height, aspect ratio preserved |
1600x1600^ | Minimum width and height, aspect ratio preserved |
1600x1600! | Forces exact width and height, ignoring aspect ratio |
1600x1600> | Shrinks only images larger than the size |
1600x1600< | Enlarges only images smaller than the size |
The same guide notes a Windows difference: Linux uses a backslash for line continuation, “whereas Windows uses a caret (^).” Copying a multi-line command from a Linux tutorial into the Command Prompt is a common source of confusing errors.
When is ImageMagick the right tool?
ImageMagick is the better choice when:
- You script it. It fits build pipelines, scheduled tasks and server jobs.
- You need effects beyond resizing. Cropping, watermarks, color changes, sharpening and hundreds of other operations.
- You need many formats. It reads and writes far more formats than a focused resizer.
- You work across operating systems. The same commands run on Windows, macOS and Linux.
- Free matters most. It costs nothing.
It is a weaker fit when the person resizing images is not comfortable in a terminal, or when one wrong command can overwrite a client’s only copy.
How is OpticBatch different?
OpticBatch is a bulk image resizer and converter for Windows 10 and Windows 11. Its Microsoft Store listing describes:
- Format support for JPEG, PNG and WebP, converting between them natively.
- Four sizing modes: Max Width, Max Height, Percentage Scale or Exact Dimensions, with an aspect-ratio lock to prevent distortion.
- A quality slider from 1 to 100 for lossy formats, with a live estimate of file size savings before you start.
- Fault-tolerant batches. A corrupted file is isolated and flagged with an error badge, and the rest of the batch carries on.
- Atomic writes. Original files are never overwritten or corrupted, even if a batch is cancelled or interrupted.
- A small footprint, under 40 MB, with no Electron or Java runtime.
- Local processing, with no forced account and no telemetry.
The safe defaults of a careful script, without writing the script.
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ImageMagick vs OpticBatch at a glance
| ImageMagick mogrify | OpticBatch | |
|---|---|---|
| Interface | Command line | Windows app, drag and drop |
| Originals by default | Overwritten, unless you use -path or -format | Never overwritten |
| Fit within a box | WxH geometry | Max Width or Max Height |
| Scale by percentage | 50% | Percentage Scale |
| Exact size | WxH!, ignores aspect ratio | Exact Dimensions, with aspect lock option |
| Quality control | -quality value | Slider 1 to 100 with size estimate |
| Bad file in the batch | Depends on the command and error | Isolated and flagged, batch continues |
| Formats | Very many | JPEG, PNG and WebP |
| Other edits | Hundreds of operations | Focused on resize and convert |
| Platforms | Windows, macOS, Linux | Windows 10 and 11 |
| Price | Free and open source | One-time purchase |
A safe batch resize workflow in OpticBatch
- Install OpticBatch from the Microsoft Store.
- Drop the folder of images onto the app.
- Choose the output format: JPEG, PNG or WebP.
- Pick a sizing mode. For web images, Max Width is usually the simplest.
- Set the quality and watch the size estimate.
- Start the batch. Any bad file gets an error badge, and the rest finish.
- Check the output. Your originals are where you left them.
Converting formats at the same time? See our guide to converting WebP to JPG in bulk. Coming from Windows’ own right-click resizer? Read OpticBatch vs PowerToys Image Resizer.
Common mistakes with batch resizing
- Running mogrify on the only copy. Use
-pathor work on a copy of the folder. - Forgetting the quotes around
>on Windows. The Command Prompt treats>as redirection. - Using
!by accident. It forces exact dimensions and can squash images. - Enlarging small images. Use
>in ImageMagick, or a maximum size in OpticBatch, so small images stay sharp. - Setting quality too low. Check a few images at full size before you resize thousands.
Frequently asked questions
Does ImageMagick mogrify overwrite the original files?
Yes, unless you change the file suffix with -format or write to another folder with -path. The mogrify documentation says so explicitly.
How do I resize images to a maximum width with ImageMagick?
Use a geometry with only the width, such as -resize "1600>". With >, only images wider than 1600 pixels are shrunk, and the aspect ratio is kept.
Is there a GUI alternative to ImageMagick for Windows?
Yes. OpticBatch is a Windows app for batch resizing and converting JPEG, PNG and WebP. IrfanView’s batch mode is another option. See our local alternative to IrfanView comparison.
Does OpticBatch support formats beyond JPEG, PNG and WebP?
Its Store listing names JPEG, PNG and WebP. If you need other formats, ImageMagick is the broader tool.
Does OpticBatch upload my images?
No. It processes images locally on your PC, with no forced account and no telemetry.
Try OpticBatch
Get OpticBatch from the Microsoft Store. It is a one-time purchase, and the Store listing shows the current price.
Resize a whole folder in a few clicks, with your originals safe.
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ImageMagick is a trademark of its owners. Microsoft, Windows and PowerToys are trademarks of the Microsoft group of companies. IrfanView is a trademark of its owner. OpticBatch is not affiliated with or endorsed by them.
Last updated 19 October 2026. Published by Automata Labs, a software company in Canada.