I’m not very good at naming effects. A friend told me it looked like a digital flower… and I put that name. In this tutorial I will teach you how to do it in Krita, but you can also try it in Gimp, there will be little difference.
Before opening Krita, we will need two Gimp gradients, called: Blinds and Greens. On Windows you’ll find them at: C:\Program Files\GIMP 2\share\gimp\2.0\gradients. Copy the two gradients to: C:\Users\Username\AppData\Roaming\krita\gradients. When you open Krita, both gradients are already available (A).
Open a new file, the size is your choice, but the Width and Height must be the same for the effect to work. In the example, my file is 900 x 900 pixels, with 300 dpi resolution. Background color doesn’t matter, I chose red. Another important thing: activate the option “Snap Image Center”, in View > Snap To (B), in this way the gradients will be applied from the center of the image.
Let´s go! In the toolbox, select the Gradient Tool (blue circle). In the top bar, click the gradient button (indicated by the blue arrow) and from the list choose the Blinds gradient (C). Go on the right side of the your screen, in “Tool Options” (D). In “Shape”, select "Reverse Spiral" (1) and in "Repeat:", choose: “Forwards” (2) and leave the rest as shown in the image (3 and 4). (Thank you, Ahab and Sooz! )
I reduced the image just to make it more obvious what will be done. As I said before, the background color doesn’t matter: anyway, the gradient will cover it. To apply the gradient, click on the center of the image (E), hold the Shift key and drag horizontally to the right, to the edge of the image. Release the mouse button and the gradient will be applied. If everything went well, your image will look like the picture on the right.
In the layers docker (F), create a new Paint Layer (1), for that click on the button indicated by the blue arrow. On this new layer we will apply the same gradient, but with the Radial shape: just change to this option, in “Shape”, in “Tool Options” (G). The way of applying the gradient is also similar to the previous one. The only difference is that you will have to drag a little more outside the image (H).
There is the applied gradient (I). Now change the layer mode from Normal to Difference (1) and… the magic happens (2)!
Cool…but this needs some color! Create one more Paint Layer (J), it will be our third layer. Choose the Greens gradient (1). This time you don’t need to change anything in the “Tool Options”. Apply the gradient in exactly the same way as you did last time and you will get the result shown in Figure K.
Change the layer mode from Normal to Grain Merge and reduce the Opacity to 63% (L), this will colorize the layers below. In Gimp, to achieve the same result, set the opacity to 80 or 75%. In the layers docker, right-click on the top layer and choose “New Layer From Visible” (M).
Krita will create a fourth layer, "Visible", on top of all the others (N). Next, check for imperfections in your image (1). If there is, apply a Gaussian Blur (in Filter > Blur > Gaussian Blur). How much to apply? It depends on your image. Try to strike a balance: we want to remove the serrations, but without smudging too much. I used the value of 2.80 pixels (O).
Next, we will apply a G´MIC filter, present in Krita itself. To access it, go to Filter > Start G´MIC-Qt (P). The name of the filter is the “Barbouillage Paint Daub”, from the “Artistic” Group (1). I didn’t change any filter settings, I simply clicked OK (2).
There is the result (Q). Moving on: in the Toolbox, choose the Transform Tool (blue circle). Click somewhere inside your image (1) and, in the frame that appears, choose: “Horizontal Mirror” (2)…
… so that our image is mirrored (R). Change the layer’s mode from Normal to Grain Merge and reduce the Opacity to 75% (1). It’s almost done (2).
Then right-click on the top layer and choose: "Flatten Image" (S). Our image will revert to having only one layer, as in the beginning (1). Now, we will use a selection tool to separate the central region…
In the Toolbox, take the Elliptical Selection Tool (blue circle). In “Tool Options” (T), choose equal values for “Width” and “Height” (1) and click on the padlock icons (2), to get a perfect circle. When you click on the image, the circle will be created: just drag it to the center of the image.
Right-click the layer and choose Add > Add transparency Mask (U). This will apply a mask to our layer (1), i.e.: everything outside the circular selection will still exist, but will be invisible to us. In this case, that part of the image will become transparent (2).
Let’s apply more colors! Create a new Paint Layer (V) and activate the second icon (blue arrow): this way, everything you paint will be within the limits of the circle. To paint, choose the colors and brush you want. I used shades of blue and light orange, applied with Airbrush (1), with Opacity of 25% and Size of 175 pixels.
Also to match the colors with the bottom layer is your choice. You can simply reduce the opacity of the top layer, as I did in the example below on the left… or change the mode of this layer and using different opacities.
For my final result, I added shades of red and used the Grain Merge mode with an opacity of 70%: