Photoshop: Resizng Images
I have found that one of the easiest ways to resize pics in Photoshop is by just using the crop button without actually cropping anything out of the image.
What makes this method work is being able to make use of the width and height parameters for this tool.
Let’s say for example you have a 4000 X 3000 pixel photo that only needs to be 700 pixels wide to span the full width of your page content. There’s no reason to upload the full size pic for example, to WordPress or downsize the image with html attributes. All you need to do is set the width parameter of the crop tool to 700px, leave the height parameter empty, drag over the entire image and hit enter.
It’s always a good plan to copy any pictures you plan to use for resizing into a new location and preserve your full resolution pics. You may want them for other applications.
Another handy application for this method is for header and sliders images in various WordPress themes. Some of these themes call for exact pixel dimensions on images so that they render correctly. In these instances you can enter the specific width and height for the cropping parameters in the toolbar and select what you want in the crop frame. The resulting cropped image will be ready to upload to WordPress with the exact dimensions.