Cache image size is larger than the original

Question

I checked my site on google page insights and it tells me that i should optimize some images. So i optimized the relevant images in the media/catalog/product directory. As the images get served from the media cache directory I flushed the catalog images cached and the magento cache and then rechecked, Still it's there. Then when i checked the cached image becomes larger in size than the original. Why is it happening? And how can i make the optimized image come to cache image directory?

Answer 1

I found a possible solution. We saved all our jpgs with a quality of 80% with photoshop. The Magento Helper inits the product image and the default quality is set to 100%. In my opinion the helper saves the image with quality 100% to the cache, and because of this the filesize is larger than the original.

Loading images like that fixed the issue for us:

Mage::helper('catalog/image')->init($_product, 'image')->setQuality(80);

Furthermore we had to override getGalleryImageUrl function of the Product_View_Media_Block to apply the fix to the gallery images.

class Custom_Images_Block_Catalog_Product_View_Media extends Mage_Catalog_Block_Product_View_Media {
    /**
     * Fix for Images -> setQuality(80)
     *
     * @param null|Varien_Object $image
     * @return null|string
     */
    public function getGalleryImageUrl($image)
    {
        if ($image) {
            $helper = $this->helper('catalog/image')
                ->init($this->getProduct(), 'image', $image->getFile())
                ->keepFrame(false)
                ->setQuality(80);

            $size = Mage::getStoreConfig(Mage_Catalog_Helper_Image::XML_NODE_PRODUCT_BASE_IMAGE_WIDTH);
            if (is_numeric($size)) {
                $helper->constrainOnly(true)->resize($size);
            }
            return (string)$helper;
        }
        return null;
    }

}

If we open the edited jpg with 80% quality with photoshop again and do a save with 100% we got the same filesize as the image of the magento cache has.

hope this fix is helpful for someone...