I have been searching the web for hours now and I have yet to find a solution. I want to apply barrel distortion to a live feed from a USB web cam (Logitech 9000), I am currently using OpenCV. I am fairly new to OpenCV so be gentle.PS I am writing this in C++ (Visual Studio 2010)Brenden Geary

(sorry chances are it is possible but it made me think of this quote)

Here's a wiki link:http://en.wikipedia.org/wiki/Distortion_(optics)#Software_correctionAnd here's a little piece from Oculus' warp shader in Unity (not including chromatic aberration correction): float2 _Center = float2(0,0); float2 _ScaleIn = float2(0,0); float2 _Scale = float2(0,0); float4 _HmdWarpParam = float4(0,0,0,0); // Scales input texture coordinates for distortion. // ScaleIn maps texture coordinates to Scales to ([-1, 1] * scaleFactor), // where scaleFactor compensates input for K1 and K2, to allow full screen size to be used. // Scale factor that fits into screen size can be determined by solving this // equation for Scale: 1 = Scale * (K0 + K1 * Scale^2 + K2 * Scale^4). float2 HmdWarp(float2 in01) { float2 vecFromCenter = (in01 - _Center) * _ScaleIn; // Scales to [-1, 1] float rSq= vecFromCenter.x * vecFromCenter.x + vecFromCenter.y * vecFromCenter.y; float2 vecResult = vecFromCenter * (_HmdWarpParam.x + _HmdWarpParam.y * rSq + _HmdWarpParam.z * rSq * rSq); return _Center + _Scale * vecResult; } Where _Center is set to:0.5f + (LensOffsetLeft * 0.5f)(left eye)and 0.5f + (LensOffsetRight * 0.5f)(right eye), where LensOffset* values are calculated from: float halfHSS = HScreenSize * 0.5f; float halfLSD = LensSeparationDistance * 0.5f; leftOffset = (((halfHSS - halfLSD) / halfHSS) * 2.0f) - 1.0f; rightOffset = (( halfLSD / halfHSS) * 2.0f) - 1.0f;where LensSeparationDistance is retrieved directly from the SDK via OVR_GetLensSeparationDistance().And, where _Scale, _ScaleIn, and _HmdWarpParams are calculated like this: _Scale.x = (NormalizedWidth / 2.0f) * distortionScale; _Scale.y = (NormalizedHeight / 2.0f) * distortionScale * aspectRatio; _ScaleIn.x = (2.0f / NormalizedWidth); _ScaleIn.y = (2.0f / NormalizedHeight) / aspectRatio; _HmdWarpParam.x = DistK0; _HmdWarpParam.y = DistK1; _HmdWarpParam.z = DistK2;where NormalizedWidth and NormalizedHeight are 1.0f for Unity, possibly different for other rendering engines,and where distortionScale is calculated such that the post-warp image fits the screen to some extent,and where aspectRatio is the aspectRatio of the screen resolution shown to one eye (width / 2 by height)and where DistK0, DistK1, and DistK2 are distortion coefficients retrieved directly from the SDK's OVR_GetDistortionCoefficients() function.I'm sure I left out some details, but it's all there in Oculus's Unity integration code if you want to see more!

I understand that part of it but my question is how can I incorporate that into/with opencv or did I miss something?Brenden Geary

There's code here that demonstrates loading an OpenCV image into an texture. Then it's a matter of rendering that texture onto something in the OpenGL scene. I'm working on something very similar for an augmented reality view, using OpenCV to process depth and color streams to allow for interaction with the rendered UI.

Hey There,Thank you for the explanation given about the hmdwrap....but I got bit of a problem, I am not on Unity and some of the math operations you are using are not defined in standard vector math...so I am kind of guessing how Unity interprets this operations... in01 = Texture Coordinates ..Vector(x,y)_ScaleIn = Vector(x,y)_Center = Scalar following this lineeg for left: _Center = 0.5f + (leftOffset * 0.5f);float2 vecFromCenter = (in01 - _Center) * _ScaleIn;Now I do not get the point of this expressions:1. (Vector1 - Scalar1) => Substract Scalar from Vector is not defined...what kind of mathematical Operation is happening here and what is the result?2a. In case (Vector1 - Scalar1) = Vector2, I get Vector2 * _ScaleIn =>multiplication of two vectors is not definedcould be a cross product (which does not make sense) could be multiplication of the coordinates of the vectors like this Vector2.x * _ScaleIn.x and Vector2.y * _ScaleIn.y ....But what is it???2b. In case (Vector1 - Scalar1) = Scalar2, I get Scalar2 * _ScaleIn => which is a valid term multiplication of Vector with Scalar.

Barrel Distortion | Meta Community Forums

13 Replies

rudi
Honored Guest
12 years ago
thx jherico!
divby0
Honored Guest
12 years ago
"jherico" wrote:
"rudi" wrote:
Now I do not get the point of this expressions:

In GLSL you can apply a scalar against a vector with an operation and it and it applies the operation piecewise to the vector components.

Close, but not quite: the scalars are implicitly cast to vectors of the correct dimension with every element containing the scalar value. The end result is the same as what you've described, but the docs won't make sense if you don't know that casts are involved.
Pernar
Honored Guest
12 years ago
First of all sorry for ressurecting this old dead horse of a thread but I am new here and the FAQ said newbees are to find threads similar to what they need and comment there. So here it goes:

I am actually after a way to replicate the Rift distrotion in GIMP using the FIlters -> Distorts -> Lense Distortions

So far I have played around with the filter a bit and I know I am on the right track but just cant figure out the correct values for 'Main', 'Edge' and 'Zoom'.

Can someone please tell me the exact values here? Or even the specific physical properties of the optics used in the Rift would be helpfull.

Many thanks!

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Barrel Distortion

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