java - 为什么 C++ 和 Java 版本的结果不同？

Question

我在 C++ ndk 中实现了 Java 图像过滤器代码，但结果不同。两者的值都是 70。

Java 版本:

public Bitmap applyContrastEffect(Bitmap src, double value) {
    // image size
    int width = src.getWidth();
    int height = src.getHeight();
    // create output bitmap
    Bitmap bmOut = Bitmap.createBitmap(width, height, src.getConfig());
    // color information
    int A, R, G, B;
    int pixel;
    // get contrast value
    double contrast = Math.pow((100 + value) / 100, 2);
    // scan through all pixels
    for (int x = 0; x < width; ++x) {
        for (int y = 0; y < height; ++y) {
            // get pixel color
            pixel = src.getPixel(x, y);
            A = Color.alpha(pixel);
            // apply filter contrast for every channel R, G, B
            R = Color.red(pixel);
            R = (int) (((((R / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
            if (R < 0) {
                R = 0;
            } else if (R > 255) {
                R = 255;
            }

            G = Color.red(pixel);
            G = (int) (((((G / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
            if (G < 0) {
                G = 0;
            } else if (G > 255) {
                G = 255;
            }

            B = Color.red(pixel);
            B = (int) (((((B / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
            if (B < 0) {
                B = 0;
            } else if (B > 255) {
                B = 255;
            }
            int val = Color.argb(A, R, G, B);
            // set new pixel color to output bitmap
            bmOut.setPixel(x, y, val);
        }
    }

    // return final image
    return bmOut;
}

C++ 版本:

int* ContrastFilter::procImage() {
double value = 70;
double contrast = pow((100 + value) / 100, 2);
int A, R, G, B;

for (int i = 0; i < width * height; ++i) {
    //__android_log_print(ANDROID_LOG_VERBOSE, "Contrast Filter","The before color is %d", this->pixels[i]);
    Color color(this->pixels[i]);
    A = color.alpha();

    R = color.R();
    R = (int) (((((R / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
    if (R < 0) {
        R = 0;
    } else if (R > 255) {
        R = 255;
    }

    G = color.G();
    G = (int) (((((G / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
    if (G < 0) {
        G = 0;
    } else if (G > 255) {
        G = 255;
    }
    B = color.B();
    B = (int) (((((B / 255.0) - 0.5) * contrast) + 0.5) * 255.0);
    if (B < 0) {
        B = 0;
    } else if (B > 255) {
        B = 255;
    }

    this->pixels[i] = ARGB2Color(A, R, G, B);
}

return this->pixels;

Java C++ 接口(interface):

public static Bitmap changeToContrast(Bitmap bitmap) {
        int width = bitmap.getWidth();
        int height = bitmap.getHeight();
        Bitmap returnBitmap = Bitmap.createBitmap(width, height, bitmap.getConfig());
        int[] pixels = new int[width * height];
        bitmap.getPixels(pixels, 0, width, 0, 0, width, height);

        int[] returnPixels = NativeFilterFunc.contrastFilter(pixels, width,
                height);
        returnBitmap.setPixels(returnPixels, 0, width, 0, 0, width, height);

        return returnBitmap;

    }

Java 结果:

C++ 结果:

我不明白为什么结果不同。我调试的时候看到有些像素值不一样，为什么计算公式一样会出现这种情况？

Answer 1

R = Color.red(pixel);
...
G = Color.red(pixel);
...
B = Color.red(pixel);

您正在为 Java 代码中的每种颜色取红色值。您可能想要调整它以获取正确的值，而不是像这样:

R = Color.red(pixel);
...
G = Color.green(pixel);
...
B = Color.blue(pixel);

旁注:根据 Java 约定，变量名应以小写 字母开头。