Step 1. Here is the brown-eyed-susans image that Kim gave us to use. This became my background layer when I opened it.
Step 2. In keeping with what Kim did in her example, the next thing I did was to crop the image into a square shape. I used the Crop tool and held down the shift key while selecting the crop area in order to restrain the region to a square.
I accepted the crop and ended up with this as my image to work with.
Step 3. Then I selected the Single Row Marquee Tool from the Tool Bar. If your Rectangular Marquee Tool is showing, click on it and hold down the mouse to show all the tools in that box. Select the Single Row Marquee Tool.
Then, in the image with the background layer active, click over a place that you want to select a single pixel wide row across the image. Select this by looking at the colors across the image and seeing what the colors would be if you have a whole row across at that point. When you click the tool, you will see the marching ants around the single pixel row that is selected. It is hard to see in the image, but the selection is there.
Step 4. Then use Command / Control - J to copy that selection of single row to its own layer.
Then, with this layer active, use Command / Control - T to active the Free Transform for the single row. Grab the top middle handle of the transform and drag it upward to extend the pixels up to the top of the image.
Then grab the bottom middle transform handle and drag it down to the bottom of the image. Accept the transform and you now have this.
Step 5. Turn off the visibility of this transformed single row by clicking on the eyeball in front of the layer. Make the background layer the active layer again. Now select the Single Column Marquee Tool from the Tool Bar.
Using the Single Column Marquee Tool, click in the image to make a selection of a column that is one pixel wide. Next, Use Command / Control - J to put the selection on its own layer. Then, with this layer active, use Command / Control - T to active the Free Transform for the single column. Grab the middle right handle of the transform and drag it to the right to extend the pixels to the edge of the image. Then grab the middle left transform handle and drag it to the left of the image. Accept the transform and you now have this.
Step 6. Turn on the visibility of the single row layer by clicking where the eyeball would be and make this the active layer. Then change the layer blend mode to Divide and leave Opacity at 100%. You now have this.
Step 7. Then I used Command / Control - E to merge this layer with the layer below it. And now I have only two layers instead of three.
Then I set this layer's blend mode to Divide and changed the Opacity to 50%, for this.
Step 8. Then I made the background layer the active layer and used Command / Control - J to duplicate the layer onto a new layer. Then I moved the duplicate layer to the top of the layer stack by clicking on it and dragging it to the top.
Then I changed the layer blend mode to Multiply with Opacity 100%, for this.
But, this made it a little too dark for me and I changed the Opacity to 70%, for this.
And this is what I was looking for for my tweaked image.
So, I started with this image.
And, ended with this image.
I hope that you enjoyed seeing how I tweaked the image. Hopefully you may even have learned a new trick or two.
Enjoy what you do.