双三次插值结果与FFMPEG不同

Question

我刚刚实现了双三次插值来调整图像大小。我有一个 6x6 像素(灰度(的测试图像，它的列是黑白 (x3(。我正在将我的代码结果与工具 ffmpeg 的结果进行比较，但它们不正确。我不明白为什么，我想我可能计算了错误的像素邻域，或者可能是调整大小的像素与原始像素的距离。有人可以查看我的代码(我将简化它以更好地阅读(并告诉我错误在哪里吗？

    // Iterate through each line
    for(int lin = 0; lin < dstHeight; lin++){
        // Original coordinates
        float linInOriginal = (lin - 0.5) / scaleHeightRatio;
        // Calculate original pixels coordinates to interpolate
        int linTopFurther = clamp(floor(linInOriginal) - 1, 0, srcHeight - 1);
        int linTop = clamp(floor(linInOriginal), 0, srcHeight - 1);
        int linBottom = clamp(ceil(linInOriginal), 0, srcHeight - 1);
        int linBottomFurther = clamp(ceil(linInOriginal) + 1, 0, srcHeight - 1);
        // Calculate distance to the top left pixel
        float linDist = linInOriginal - floor(linInOriginal);
        // Iterate through each column
        for(int col = 0; col < dstWidth; col++){
            // Original coordinates
            float colInOriginal = (col - 0.5) / scaleWidthRatio;
            // Calculate original pixels coordinates to interpolate
            int colLeftFurther = clamp(floor(colInOriginal) - 1, 0, srcWidth - 1);
            int colLeft = clamp(floor(colInOriginal), 0, srcWidth - 1);
            int colRight = clamp(ceil(colInOriginal), 0, srcWidth - 1);
            int colRightFurther = clamp(ceil(colInOriginal) + 1, 0, srcWidth - 1);
            // Calculate distance to the top left pixel
            float colDist = colInOriginal - floor(colInOriginal);
            // Gets the original pixels values
            // 1st row
            uint8_t p00 = srcSlice[0][linTopFurther * srcWidth + colLeftFurther];
            // ...
            // 2nd row
            uint8_t p01 = srcSlice[0][linTop * srcWidth + colLeftFurther];
            // ...
            // 3rd row
            // ...
            // 4th row
            // ...
            // Bilinear interpolation operation
            // Y
            float value = cubicInterpolate(
                cubicInterpolate(static_cast<float>(p00), static_cast<float>(p10), static_cast<float>(p20), static_cast<float>(p30), colDist),
                cubicInterpolate(static_cast<float>(p01), static_cast<float>(p11), static_cast<float>(p21), static_cast<float>(p31), colDist),
                cubicInterpolate(static_cast<float>(p02), static_cast<float>(p12), static_cast<float>(p22), static_cast<float>(p32), colDist),
                cubicInterpolate(static_cast<float>(p03), static_cast<float>(p13), static_cast<float>(p23), static_cast<float>(p33), colDist),
                linDist);
            dstSlice[0][lin * dstWidth + col] = double2uint8_t(clamp(value, 0.0f, 255.0f));
        }
    }

Answer 1

我忘了设置插值矩阵的二阶变量的值。它们设置为 0，因此生成的插值将类似于双线性插值。