This filter tells the image optimizer not to upscale your images. This means that if an original image is 300px width by 200px height and you ask for a 600×400 image optimizer will still return a 300×200 image.
Normal Image:
https://push-3272.5centscdn.com/KB_IMG/Lights_5centsCDN.jpg
No Upscale enabled image:
https://push-3272.5centscdn.com/KB_IMG/Lights_5centsCDN.jpg?im=filters:no_upscale()
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