---
title: "Building a JPG/PNG to WebP Converter in PowerShell (with Google's WebP Library)"
description: "How to use PowerShell with Google's cwebp tool to batch convert JPG and PNG images to WebP, and how file sizes compare across different compression quality settings."
canonical_url: "https://blog.markkulab.net/en/post/powershell-webp-conveter"
author: "Mark Ku"
author_url: "https://blog.markkulab.net/en/author/mark-ku"
site: "Mark Ku's Tech Notes"
date_published: "2021-08-07 01:01:01 +0800"
category: "PowerShell"
tags: ["powershell", "webp", "image", "converter", "optimization", "google", "frontend"]
language: "en"
license: "CC BY 4.0"
license_url: "https://creativecommons.org/licenses/by/4.0/"
attribution: "when reusing or quoting, credit the author and link back to the original"
---

# Building a JPG/PNG to WebP Converter in PowerShell (with Google's WebP Library)

## Origins of WebP
WebP was developed by Google. Its key advantage is delivering excellent visual clarity without bloating network payloads — which is critical for page load speed.

## Why use WebP
For most websites, images account for over 60% of page weight. WebP can shrink JPEG file size by ~35% and PNG file size by ~50% while preserving quality and transparency. Adopting WebP reduces bandwidth usage and improves user experience.

## File size comparison
### The cwebp tool defaults to 80% quality. Here's a comparison between lossless 100% and the default 80%.
1. JPG to WebP — Lossless WebP conversion actually grows the file size by roughly 2x. With the default 80% compression, however, file size drops by ~40%.
![File size comparison: JPG, lossless WebP, and 80% compressed Web](https://blog.markkulab.net/content/markku/posts/powershell-webp-conveter/images/pcc6KNz.png)
2. PNG to WebP — Lossless WebP cuts file size by more than half. With the default 80%, files shrink by ~86%.
![Windows dialogs comparing PNG, lossless, and 80% compressed WebP file](https://blog.markkulab.net/content/markku/posts/powershell-webp-conveter/images/1cecyod.png)  
* An interesting observation:
* The default 80% mode reduces both JPG and PNG sizes meaningfully, but the lossless 100% mode can actually double the size of a JPG.

## Browser support
A few years ago WebP support was patchy, but it's now widely supported. One thing to watch out for: iOS only added WebP support starting with version 14, so older versions need a fallback.
* [Solution for browsers without WebP support](https://medium.com/@mingjunlu/image-optimization-using-webp-72d5641213c9)  
![Can I use WebP browser support matrix by version](https://blog.markkulab.net/content/markku/posts/powershell-webp-conveter/images/P4qSTME.png)   

## Download Google's WebP tool
https://developers.google.com/speed/webp/download  
![Google's WebP download page with a highlighted download link](https://blog.markkulab.net/content/markku/posts/powershell-webp-conveter/images/Wke6lvo.png)

## Write the PowerShell script (Convert-WebP.ps1)

```
$libPath = $PSScriptRoot + "\libwebp-1.2.0-windows-x64\bin\cwebp.exe"
$defaultFoldPath = (Get-Item .)
$outputFolder = 'output'
Function Get-Folder([String] $initialDirectory)
{
    [System.Reflection.Assembly]::LoadWithPartialName("System.windows.forms")|Out-Null

    $foldername = New-Object System.Windows.Forms.FolderBrowserDialog
    $foldername.Description = "Select a folder"
    $foldername.rootfolder = "MyComputer"
    $foldername.SelectedPath = $initialDirectory
	$foldername.ShowNewFolderButton = $false
	
    if($foldername.ShowDialog() -eq "OK")
    {		
        $folder += $foldername.SelectedPath 
    }else{
		exit		
	}
    return $folder
}


Function Conver-Webp([String] $source, [String] $output)
{	
   Write-Host ('$input path:' + $source)
   Write-Host ('$output path:' + $output)

   if (!(Test-Path -Path $output )) {
   New-Item -ItemType directory -Path $output
   Write-Host 'create new folder' + $output
   }

   $files = get-childitem $source -recurse -force -include *.jpg, *.png  
   Write-Host $files
   foreach($inputFile in $files){      
	
   #Call cwebp  
   $inputFilePath = $inputFile.FullName  
   $outputFilePath = Split-Path -Path $inputFile.FullName  
   
   $outputFilePath = $output + "\" + [System.IO.Path]::GetFileNameWithoutExtension($inputFilePath) + ".webp"  
	
   # 使用 80% 品質等級去轉換單張圖片：

   Write-Host $outputFilePath  
   $args = "-q 80 " + $inputFilePath + " -o " + $outputFilePath  
  
   Start-Process -FilePath $libPath -ArgumentList $args -Wait  
  
   $originalFileSize = (Get-Item $inputFilePath).length  
   $optimizedFileSize = (Get-Item $outputFilePath).length    
     
   $savedBytes = $originalFileSize - $optimizedFileSize  
   $savedPercentage = [math]::Round(100-($optimizedFileSize / $originalFileSize)*100)  
   $message = $inputFilePath + " " + $outputFilePath + " " + $savedBytes + "bytes " + $savedPercentage + "%"  
   
   Write-Host $message   
   } 
}


$sourceFolderPath = Get-Folder($defaultFoldPath) 
$outputFolderPath =($sourceFolderPath+ '\' + $outputFolder)

Conver-Webp $sourceFolderPath $outputFolderPath 
	  
PAUSE

```  

## Place the downloaded WebP library next to the script, then right-click Convert-WebP.ps1 > Run with PowerShell
![Windows context menu for Convert-WebP.ps1, 'Run with PowerShell' highlighted](https://blog.markkulab.net/content/markku/posts/powershell-webp-conveter/images/wrtboP2.png)   
## Select the source folder
![Windows 'Select a folder' dialog, 'output' folder highlighted](https://blog.markkulab.net/content/markku/posts/powershell-webp-conveter/images/V2TuSRe.png)
## Execution screen
![PowerShell execution screen showing WebP conversion progress](https://blog.markkulab.net/content/markku/posts/powershell-webp-conveter/images/UOQZr4S.png)
## When the script finishes, all jpg/png files are written to the output directory.
![File Explorer displaying source folder containing various JPG PNG files](https://blog.markkulab.net/content/markku/posts/powershell-webp-conveter/images/JcIfmWm.png)

---

## About this article and its author

Originally published on [Mark Ku's Tech Notes](https://blog.markkulab.net/en/post/powershell-webp-conveter)

License: [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/) — when reusing or quoting, credit the author and link back to the original

### About the author

**[Mark Ku](https://blog.markkulab.net/en/author/mark-ku)** — Software Solution Provider

- 10+ years senior software engineer, now an AI Builder
- Focused on large-platform architecture — North-American e-commerce, AI SaaS subscription billing
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- [Uptime Kuma Cluster](https://blog.markkulab.net/en/tools/uptime-kuma-cluster): Turn single-node Uptime Kuma into a highly available cluster: OpenResty + Lua smart load balancing, shared MariaDB state, health checks and automatic failover, plus cluster-management REST APIs. One Docker Compose command to start. Free and open source (MIT).
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