How to draw physically and mathematically modeled soap bubble

[sunmaggot]

This tutorial is available as a PDF. Click here to view or download it

Bubble

 

 

 

Background information (ignore this part if you are not interested in the science part) :

The bubble in this tutorial is a spherical shape. The colour of the bubble surface mainly comes from the following two phenomenon. 

 

1. Thin Film Interference.

Soap bubble is a layer of soap that forms a sphere and floats in the air. Therefore it involves 3 layers of medium: Outer air, soap layer, inner air. Therefore there are two boundaries that will reflect light, outer air | soap layer outer surface   and   soap layer inner surface | inner air. Thus interference will occur because there are two reflected light rays going to your eyes.

For more information, check out https://en.wikipedia.org/wiki/Thin-film_interference

 

2. Optical effect on environmental lighting.

The environmental image formed on the bubble is actually made of the image behind observer. If you check the bubble image, you will find out there is something weird about the reflection. There are two identical images, one formed in upper hemisphere and another inverted one formed in lower hemisphere. This is due to two surface doing reflection. The image on upper hemisphere is virtual image reflected by front surface of the bubble while the inverted image on lower hemisphere is real image reflected by rear surface of the bubble. For more information, check out http://www.atoptics.co.uk/fz618.htm

 

3. There maybe Brewster's angle to consider, but this may make things too complicated so I will ignore Brewster's angle problem. I am also not so sure about the effect.

 

Tutorial Part:

 

There is no plugin needed in this tutorial but you may prepare a photo of open area for latter part, an image with a distinct object is ideal.

 

Making Bubble Shell

 

First, for convenience, we need to create a file of square canvas, in my example, I used 200x200. We want to make the bubble at the center so that some effects are easily applied without changing coordinate settings. Delete all the white colour on the background.

 

1. Make a white circle of 5 brush width with size 200x200. Make sure the whole circle is visible as some boundary may be out of bound. This is going to be the bubble size.

2. Now modify the canvas size into 400x400 with the anchor in the center. This will keep the bubble at the center.

3. Using bucket, fill the outer space with white colour (with high tolerance) so that the whole thing now looks like a big hole.

 

The black colour does not exist, but the white colour on white background is invisible, so there is black colour background to indicate what you should have.

 

4. Use Effects -> Blurs -> Gaussian Blur with 40 radius.

5. Use magic wand with 15% tolerance and select the outer white part. Then delete the selection. This is our bubble now.

 

 

Same as previous image, the black colour does not exist, it is for you to see the white colour.

 

Making Thin Film Interference Map

 

Soap bubble doesn't have a fixed soap layer thickness, therefore we can assume one for it and draw the interference at our own will. In my case, the interference pattern will go from yellow(outside) to green(inside). 

 

1. Using Shapes tools, create the follow image where yellow, red are with brush width 10 and other colours are with brush width 15. It is ideal to draw each circle on separate layer for easy modification. Keep the circles concentric but don't spend too much time to perfect the center of the circles because after effects, the center will be barely seen.

 

 

2. After you are very sure that the circles are correctly drawn, merge them all into one single layer.

 

3. Use Effects -> Distort -> Bulge with maximum bulge. It is difficult to determine how much bulge you should do, but this process is to mimic the interference mechanics. The more curvature of the surface, the more phase difference present. Repeat Bulge effect until the green colour takes around 1/4 area of the bubble (1/2 radius of the bubble shell), or not if you don't think this is important. Since this part can be a bit personal. One thing to keep in mind, the colour change in central area should be less vigorous than area around the edge.

 

 

4. Use Effects -> Blurs -> Gaussian Blur with 20 radius. 

 

5. After these effects, the interference map is enlarged. Resize it so that it fits the bubble shell with a little bit of yellow out of bubble. This is because the opacity of the outermost yellow is too low, it is ideal to remove them. Use magic wand to select the space outside bubble shell and delete the selection in the interference map.

 

 

6. Use Effects -> Distort -> Dents with tension 100 and choose the scale you want (I chose 30). This is to mimic the uneven surface thickness of the bubble leading to uneven interference pattern.

 

7. Use Gradient with transparency mode, radial mode, right click from center to purple only. Repeat it so that the green is not so obvious. Use magic wand method mentioned in step 5 to remove out of bound part.

 

 

8. Adjust layer opacity to something you feel comfortable. However, in latter part, the interference opacity will be changed. Therefore I think this is only a simplified preview for yourself.

 

Preparing environmental image on the bubble

 

To maintain originality, I am not going to pick up images from google, instead I will draw my own image. The image is going to be an ugly tree with ugly ground and ugly sky.

 

 

The image is 400x400 size, which is the whole canvas size.

 

This is probably your image size and it is too large to fit into the bubble. Therefore we must cut part of it out and fit it into the bubble. And this is the reason why an image with distinct object is ideal.

 

1. This step is a bit troublesome. You are going to take the object out, which means removing background stuff such as ground and sky. However, don't delete them, you need to use them later. I used lasso selector and magic wand to cut out the tree. Use your method to do this task, nothing really special. You can duplicate layer and remove unwanted part too.

 

 

2. resize the object to fit the right side of the upper hemisphere of the bubble shell.

 

3. duplicate this layer and use Layers -> Flip Horizontally, then use Layers -> Flip Veritcally. Now you should obtain the virtual and real image.

 

 

4. We have a problem now, we don't have ground and sky. There are two choices. One is draw them by yourself, one is copy them from your reference image. For my case, I will just draw them by myself. The procedure is simple, draw the ground layer under the tree layer, then render cloud layer under ground layer, then use magic wand to remove out of bound pixels.

 

 

5. After obtaining image, use Effects -> Distort -> Bulge with maximum bulge to distort image to fit the bubble. Then use magic wand to remove out of bound pixels.

 

6. Now you have obtained the image that fits the bubble surface. Lastly, put interference map above this layer. Then lower the opacity of this layer so that it is transparent, I used 95.

 

7. Use Gradient with transparency mode and radial mode (primary colour with maximum opacity and secondary colour with 127 opacity). Gradually decrease opacity of the central area (make sure they are not completely invisible!!!). This is similar to what we did on interference map, except the opacity of secondary colour being different.

 

 

I think you should see the bubble is coming out. However the harmony of the image must be achieved in order to make it looks like an object. We need to do some shading to the whole image.

 

Dealing with final shading

 

As mentioned in the last part of interference map, the interference map will be used again. It is time to use it again.

 

1. Create a new layer above the whole bubble, copy the interference map into this layer (or simply duplicate interference layer then adjust layer opacity to maximum).

 

2. Use Effects -> Blurs -> Gaussian Blur with 20 radius on the layer.

 

3. use gradient tools with transparency mode, with linear(reflected) mode, with both primary and secondary colour with maximum opacity, draw from center to purple with left click diagonally with direction from left top(center point) to right bottom (purple area). Note that depending on your own taste, you may drag a longer gradient. For me, I found from center to purple seems good. The reason to make such gradient is because this can mimic uneven background lighting effect without making chaotic pattern. It still keeps the reflection symmetry.

The instruction maybe a bit messy due to many settings, but overall, the following image is what you want to achieve.

 

 

4. Add a new layer with overlay blend mode on top of everything.

 

5. Use gradient tools with colour mode, with linear(reflected) mode, with primary colour being black with 127 opacity and secondary colour being white with maximum opacity. draw from center to boundary of bubble shell diagonally with direction from left top(center point) to right bottom(boundary of bubble shell). Then use magic wand to remove out of bound pixels according to bubble shell. You can also draw your own overlay colour. Overall, the black white colour should be similar to the following image.

 

 

6. Finally, add whatever you want. For me, this bubble is very good in terms of colour pattern, except that most light can pass through the central part of the bubble, maybe because it is the central axis in a lens if you treat the bubble as lens. Also the thickness of soap in central part is relatively thinner. Let's stop dealing with the geometry and go back to the main content lol.

 

7. Use Images -> Flatten

 

This is my bubble  

 

8. Use gradient tools with transparency mode, radial mode, with secondary colour non-maximum opacity (depending on your own taste), primary colour with maximum opacity. Right click drag from center to boundary, you can adjust secondary colour opacity until it is something you want. You may also place a background image to see if the bubble suits the environment.

 

 

Depending on your environmental image, there can be variant of bubble, here is another one created with similar method but with different environmental image.

 

 

Finished!!

[Eli]

More bubbles.   I did get some help from TR's Fish eye to distort the image.

[Seerose]

 @Eli! Is that you on the picture?  Very great work. Thank you so much.  

 

*I will give points tomorrow. I can not handle it sparingly.

[sunmaggot]

Ahh, I forgot to mention, if the bubbles are merged together, they must form 120 degree angle. I don't know the reason, seem like a troublesome physics behind. 

[Eli]

2 hours ago, Seerose said:

Is that you on the picture?

No, no, it is not me, otherwise it would not look that great.

[Seerose]

 @sunmaggot! 

 

Sorry! Late reacts.     Welcome to the PDN Forum. Thank you so much for the tutorial.   
Next days I will try.

[Seerose]

 @Eli! I think you're very pretty. 

[MadJik]

I did a tuto 10 years ago. I think it's still good.

[Eli]

3 hours ago, MadJik said:

I did a tuto 10 years ago. I think it's still good.

Soap bubbles have not change since.  

[MadJik]

13 minutes ago, Eli said:

Soap bubbles have not change since.  

But my girl did (change in ten years)