There have been lots of questions about the image sizes needed for use in the Divi slider, so here is a rundown of some of the suggested image sizes you need;
Image slider background.
The height of a slide is determined by the amount of text content that is in your slide. If you have more than 1 slides, then the slider will use the height of the tallest slide. If you want to force the slide to a fixed height you can add custom CSS as explained at WPThemeFAQ
The width of your slider is determined by the column structure that your slider module is placed in. Your slider images should be (at least) the width of the column that it sits in. Standard column widths are;
1 column: 1080 pixels
¾ column: 795 pixels
⅔ column: 700 pixels
½ column: 510 pixels
⅓ column: 320 pixels
¼ column: 225 pixels
For full width sliders i use 1920px by whatever height… and for full screen 1920px x 1024px.
** Enabling Parallax will give your background images a fixed position as you scroll AND your images will scale to the browser height.
You can download Perfect Image Templates For Every Situation directly from Elegant Themes.
Slide Image – If you want to also add a slide image, it will display to the left of your slide text and on top of your slide background image. If no slide image is set, then the slide text will be displayed centred. As the height of the slide is set by the amount of text on the slide, if your slide image is tall enough it will drop below the bottom of the slide, creating bottom aligned image.
Slide images will only appear in sliders that are in ⅔ column, ¾ column, or 1 column widths.
Slide images will not display on browser widths of less than 768 pixels.
The widths of slide images are;
1 column: 410 pixels
¾ column: 308 pixels
⅔ column: 260 pixels