Model/Config.php
public function isImageOptimizationPixelRatioEnabled()
    {
        if ($this->isImageOptimizationEnabled() !== true) {
            return false;
        }

        return $this->_scopeConfig->isSetFlag(self::XML_FASTLY_IMAGE_OPTIMIZATIONS_PIXEL_RATIO);
    }
public function isImageOptimizationPixelRatioEnabled()
    {
        if ($this->isImageOptimizationEnabled() !== true) {
            return false;
        }

        return $this->_scopeConfig->isSetFlag(self::XML_FASTLY_IMAGE_OPTIMIZATIONS_PIXEL_RATIO);
    }
Determines should Image optimization pixel ratios be used

@return bool