The Photoshop plug-in TinyPNG-TinyJPG from Voormedia will slim your PNGs and JPGs way down.
The plug-in costs $50 (and is worth every penny) and there is a free drag- and-drop converter on their website that can handle up to 20 files at once. Examples compared with PS save for web / PNG: Logo – was 113 K, now 6K; Flow chart – was 194K, now 54 K.
Example attached: was 369 K, now 72 K:
To convert manually choose export, select the plug-in, specify PNG or JPG and set the output location. If you set up a batch operation in Photoshop, the replace & close functions can be goofy, transforming the files but then closing without saving (a Photoshop issue). In many cases it is best to create an empty target folder on your desktop and point the batch to that folder, then copy the processed files back to the source folder.
Here's the URL: https://tinyjpg.com
One more thing – An old trick that web designers have been using for twenty years to save load time (kind of a big deal in the days of V.32bis modems) is to take a gradient that is only 1 px wide and tiling to fill a background. If we want to use a huge image, such as a PNG image of translucent clouds, you don't have to use a full-width image in your project. Depending on the image, you can distort it to a narrow width (as much as 25% for a blurry image such as soft clouds) and use Hype to stretch it to the correct proportions, thereby saving on the load time.