CImg立方子像素位置(CImg cubic subpixel location)

CImg立方子像素位置(CImg cubic subpixel location)

我试图了解代码正在做什么使用C ++ Image Processing Toolkit的 CImg.h文件从图像中提取值。

该函数使用以下语句：

float dx(float x, float y, CImg<float> &i) { float val = i.cubic_atXY(x + 0.5, y); return val; }

我认为它试图在坐标（x + 0.5，y）上找到三次插值子像素。 我发现这个函数是在CImg.h文件的第12450行附近定义的，但我真的不知道如何将它转换为其他代码，如python。

使用这种库的人能够理解它吗？

I am trying to understand what a code is doing that uses CImg.h file of C++ Image Processing Toolkit for extract a value from an image.

The function uses the following statement:

float dx(float x, float y, CImg<float> &i) { float val = i.cubic_atXY(x + 0.5, y); return val; }

I think that it is trying to find the cubic interpolated subpixel on coordinate (x+0.5,y). I found that this functions are defined near line 12450 on the CImg.h file, but I really do not not how to translate it to other code such as python.

Someone that uses this kind of libraries is able to understand it?

最满意答案

cubic_atXY是一些看起来很乏味的代码，但它基本上都是简单的算术运算，在其他编程语言中应该有类似的语法。 唯一不通用的行就是这样，例如：

const Tfloat Ipp = (Tfloat)atXY(px,py,z,c,out_value)

这是一个C风格的演员阵容。 它将调用atXY()的结果转换为Tfloat 。 顺便说一句，这看起来像双三次插值。

The atXY() call is to check that the points used to make the bicubic interpolation are inside the frame limits. The function as Carlton said and I confirmed, it is a bicubic interpolation to extract the value of a subpixel in any location inside the image. I was trying to translate the code to python, and I finally perform the following code that gives the same result of CImg.h function.

*Take into account that I implement directly the atXY() function with logical operators and that the indexes (x,y) are changed to (y,x) because python uses (idRow,idCol) for the matrix index

def bicubic(fx, fy, img): img = img.astype(float) h,w = np.shape(img) if(fx < 0 or fx > w-1 or fy < 0 or fy > h-1): val = 0 return val x = int(fx) y = int(fy) dx = fx - x dy = fy - y px = 0 if x-1<0 else x-1 py = 0 if y-1<0 else y-1 nx = x+1 if dx>0 else x ny = y+1 if dy>0 else y ax = w-1 if x+2>=w else x+2 ay = h-1 if y+2>=h else y+2 Ipp = img[py,px]; Icp = img[py,x]; Inp = img[py,nx]; Iap = img[py,ax]; Ip = Icp + 0.5*(dx*(-Ipp+Inp) + dx*dx*(2*Ipp-5*Icp+4*Inp-Iap) + dx*dx*dx*(-Ipp+3*Icp-3*Inp+Iap)) Ipc = img[y,px]; Icc = img[y,x]; Inc = img[y,nx]; Iac = img[y,ax]; Ic = Icc + 0.5*(dx*(-Ipc+Inc) + dx*dx*(2*Ipc-5*Icc+4*Inc-Iac) + dx*dx*dx*(-Ipc+3*Icc-3*Inc+Iac)) Ipn = img[ny,px]; Icn = img[ny,x]; Inn = img[ny,nx]; Ian = img[ny,ax]; In = Icn + 0.5*(dx*(-Ipn+Inn) + dx*dx*(2*Ipn-5*Icn+4*Inn-Ian) + dx*dx*dx*(-Ipn+3*Icn-3*Inn+Ian)) Ipa = img[ay,px]; Ica = img[ay,x]; Ina = img[ay,nx]; Iaa = img[ay,ax]; Ia = Ica + 0.5*(dx*(-Ipa+Ina) + dx*dx*(2*Ipa-5*Ica+4*Ina-Iaa) + dx*dx*dx*(-Ipa+3*Ica-3*Ina+Iaa)) val = Ic + 0.5*(dy*(-Ip+In) + dy*dy*(2*Ip-5*Ic+4*In-Ia) + dy*dy*dy*(-Ip+3*Ic-3*In+Ia)) return val