Using ImageOptim for reducing image file sizes

When it comes to website performance, it’s important to ensure that you’re making as few page requests as possible, and that assets are minimized and optimized to the greatest extent possible. This is true of both source code files such as CSS and JavaScript, as well as your image assets. Making sure your images are only as large as necessary (whilst maintaining high quality resolution) will go a long way in improving your site load times, improving your user experience and the likelihood users will remain on your site / visit again. This post will give an overview of the ImageOptim application and web service for making your images load faster without the cost of reduced image quality.

Getting Started

ImageOptim reduces image files sizes by removing unnecessary metadata such as digital camera metadata, embedded thumbnails, comments and other content. Removing this data on its own will significantly reduce file sizes without having to alter the image’s resolution in any way. Even images “Saved for Web” in Photoshop or similar applications can be further reduced with ImageOptim.

ImageOptim comes in two versions: a free, donation-based application for Mac OS X (10.9+), and a subscription-based web service for any platform. For Windows and Linux users, FileOptimizer and Trimage are decent alternatives that use many of the same compression tools as ImageOptim.

Once you have the application installed, you can start optimizing files just by dragging them onto the open application window. Alternatively you can also drag files directly onto the dock icon in Mac OS X.

Using ImageOptim for reducing image file sizes

ImageOptim optimizes the files you select, so if for some reason you want to keep copies of the original pre-optimization, it’s best to make copies to optimize first.

Using ImageOptim for reducing image file sizes

ImageOptim can also be opened via the command line, by running the following command from your terminal:

open -a ImageOptim .


ImageOptim’s default settings will work fine for most uses, although you may want to adjust the many built-in preference settings depending on your requirements. For example, if you’d like to keep in copyright information on your images, de-select the “Strip JPEG metadata” option from the General tab in preferences. This will result in a larger file size, though.

Using ImageOptim for reducing image file sizes

By default ImageOptim reduces file sizes with lossless compression, leaving the original image quality completely unaffected. If a smaller file size is desired over maintaining image quality, it is possible to enable “lossy minification” via the Quality tab in preferences. The lossy minification option is similar to the results of online services such as You can adjust the quality for the three most common image formats (jpeg, png and gif), at the cost of a lower image quality. You can play around with these settings to find the best balance between file size and image resolution.


While there are many services and plugins that offer image optimization, having a desktop-based application is a convenient and reliable way to optimize large amounts of images without relying on a web service or plugin. This makes ImageOptim a great choice for image optimization regardless of the ultimate platform or application your image assets will be used for.


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