I have tried everything I can think of, but when I reduce resolution of graphics, keeping the same dimensions, it has no effect on the size of the file. This makes no sense. I prepare graphics for the web and so I often want to drop some weight by lowering the resolution of an image from, say, 300 ppi to 72 ppi. It would seem, intuitively, that this would lower the size of the file. Yet, when I do it, the file size stays the same. If you’re using a set amount of pixels, let’s say 500 x 500, it won’t matter whether you’re using 300 ppi or 72 ppi because the amount pixels in the image would still be 500. If you wan’t to lower the file size of your image you will either need to scale down the image or save the image in a lower quality format: Or use Save for Web as this can give you a finer degree of tweaking with your image quality as you save: Raster images (which is what Photoshop works on) are stored as pixels. The more pixels, the larger the file size. The ppi (pixels per inch) affects how the image appears on paper. By increasing this number, the pixels get smaller when printed. However, changing this number does not affect the number of pixels. If you have a 1920 x 1080 pixel image, the file size will be the same whether you have the image set to 72ppi or 300ppi. The only difference is how big the pixels will be when printed. To reduce the file size by changing the resolution, you need to change the number of pixels. By keeping the width:height ratio the same, your image will have the same aspect ratio when resized. So you could change a 1920 x 1080 image to 1280 x 720, and the number of pixels (and file size) would be only about 44% of the original. Interestingly, you could create a design with 72dpi and when done, flatten all layers, then rasterise. This reduces the image 60% more. I found this solution from self discovery, it works. We recently did a comparison of major file optimization apps – https://www.oss-usa.com/blog/faster-sites-are-way-better-slower-sites While Photoshop can do file optimization, it is not the ideal tool to get it done – there are specific add ons and free services that can get the job done even better. Source.