Image Warping - Bulge Effect Algorithm

Question

Can any point to image warping algorithms? Specifically for bulge effect?

Denyse

May you help me with this? stackoverflow.com/questions/70683954/how-can-i-do-image-warp – Ngocnguyen

Answer 1

See if I understood what you want. Suppose your image coordinates go from 0 to 1.

If you do:

r = Sqrt[(x - .5)^2 + (y - .5)^2]
a = ArcTan[x - .5, y - .5]
rn = r^2.5/.5 

And then remap your pixels according to:

  x -> rn*Cos[a] + .5 
  y -> rn*Sin[a] + .5  

You get:

You may adjust the parameters to get bigger or smaller bulges.

Edit

Let's see if I understood your comment about warping. The following images are generated using

rn = r^k {k: 1 ... 2}: 

Thorium

You don't really need to go into trigonometry. Cos[a] = (x - .5)/r and Sin[a] = (y - .5)/r – Volscian

Check the algorithm in this link - davis.wpi.edu/~matt/courses/morph/2d.htm Can we have an algorithm like this for bulge effect? – Denyse

Thanks belisarius. I now need to implement it by adding a mesh to a Sprite in Android and applying the deformation to it. We have a library called andEngine which we can utilize. I have created another thread to proceed further: #5078740 – Denyse

@user193545 Can't help you wih that one. Good luck! – Thorium

See also my followup to this answer here – Kristalkristan

Can you explain as briefly with any example – Gillian

I am unable to get above effect by using your alogorithm. – Kistler

@belisarius Can you help me with detecting the Objects shape witin an image ? – Finkelstein

@Ajay May be. Post a question and ping me again :) – Thorium

@belisarius I'm interested in garnering a deeper understanding of the math involved in the image warp you describe above; I've opened a thread over at math.stackexchange.com to that end: math.stackexchange.com/questions/266250/… I'd really appreciate your input! Thanks very much! – Interest

Answer 2

GLSL code version:

uniform sampler2D tex;

void main()
{
 vec2 cen = vec2(0.5,0.5) - gl_TexCoord[0].xy;
 vec2 mcen = - // delete minus for implosion effect
      0.07*log(length(cen))*normalize(cen);
 gl_FragColor = texture2D(tex, gl_TexCoord[0].xy+mcen);
}

original:

explosion:

implosion:

cheers!

Wetmore

how to use it in Android with bitmap? – Fanning