OK - closing in here on understanding this - which has involved a little J51 learning plus some Photoshop learning.
First - thanks for the tip on the Firefox "View Image Info." That's so helpful - both for assessing my own image sizes at a glance, and also from learning from yours and other websites.
In looking at your demos for the templates I'm using, I observe the following:
1) In Renovate (used by morninglightmusic.org) your 4 slideshow images vary from 81-162 px. All show dimensions 1000 px x 638 px, scaled to 1216 px to 736 (remarkably similar to the 1200 x 750 px image size I happened on for my site, by trial and error, trying to "eyeball" and replicate the sizes on your demo.) I'm guessing your 1000x638 was generated by downloading the "Medium" size Shutterstock image? If so, what creates the "scaled to" dimension - which it appears is the actual viewed dimension on the site? Is that "scaling" set in Photoshop? I saw another tutorial on YouTube on increasing image size for increased clarity on a smaller image. What I did was download "Large" size Photoshop images and cut their dimension sizes. Obviously, this means I'm stuck with a bigger size original image on my computer. So if it's possible to work from "Medium" sized images for these bigger slide shows I'm all for that. Help me understand "scaling" in this context?
2) In LetterPress (used by my morninglightcounseling.com) your images vary in size from 82-139 KB, "1000 px x 550 px, scaled to 1216 x 669 px.) So - same question on scaling. And - both Renovate and Letterpress default to "100% yes." Please help me understand the difference between image size, file size, scaling, and 100% yes or no.
3) In Habitat (used by my impactmusic4kids.org) your images vary from 70-113 KB, all set to 1080x422 (no scaling mentioned.) What is the difference here? Also, 100% is off - I assume because you want the background to display on the sides of the slideshow?
4) In Brooklyn thing - your images are 89-95 KB, all set to 1100 px x 450 px. So - did you expand a Shutterstock Medium (1000 px wide) image in Photoshop in some way to accomplish this? Is that the same or different than the "scaling" observed in Renovate? (I see the same thing in Lifestyle - non scaled images all set to 1080x300 px sizes, without scaling. Trying to understand the process here.)
So my question now is - when do you "scale" an image, or not; do you set the slideshow settings to match established image sizes (like 1100 px by 450 px) ; is 100% No basically when you want a margin on each side, vs. 100% Yes if you want the image all the way right to left?
I've learned from the Photoshop tutorial to : 1) set resolution to 72; 2) set document widths; 3) set compression levels to reduce file size. Now I'm trying to understand how that "scaling" fits in. I'm "almost there" understanding this core issue of establishing image sizes for the slideshows - such a key component of these lovely templates. If you could help me understand these pieces I'd be most grateful. Hoping to finish these slideshows (and hence the sites) by tonite.