C语言彩图转换灰度图

用C语言作灰度变换，图片变成这样了，转换其他图片转换正常，以下为源码

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define getLineBytes(biWidth, biBitCount) (biWidth * biBitCount / 8 + 3) / 4 * 4;
#pragma pack(1)

typedef struct tagBITMAPFILEHEADER {
    unsigned char bfType[2];
    unsigned long bfSize;
    unsigned short bfReserved1;
    unsigned short bfReserved2;
    unsigned long bfOffBits;
} fileHeader;

typedef struct tagBITMAPINFOHEADER {
    unsigned long biSize;
    long biWidth;
    long biHeight;
    unsigned short biPlanes;
    unsigned short biBitCount;
    unsigned long biCompression;
    unsigned long biSizeImage;
    long biXPixPerMeter;
    long biYPixPerMeter;
    unsigned long biClrUsed;
    unsigned long biClrImportant;
} fileInfo;

typedef struct tagRGBQUAD {
    unsigned char rgbBlue;
    unsigned char rgbGreen;
    unsigned char rgbRed;
    unsigned char rgbReserved;
} rgbq;

void readBMP(FILE *fpBMP, fileHeader *fh, fileInfo *fi, rgbq *fq) {
    fread(fh, sizeof(fileHeader), 1, fpBMP);
    fread(fi, sizeof(fileInfo), 1, fpBMP);
    long oldBiWidth = getLineBytes(fi->biWidth, fi->biBitCount);
    fi->biBitCount = 8;
    long newBiWidth = getLineBytes(fi->biWidth, fi->biBitCount);
    fi->biSizeImage = newBiWidth * fi->biHeight;
    fh->bfOffBits = sizeof(fileHeader) + sizeof(fileInfo) + 256 * sizeof(rgbq);
    fh->bfSize = fh->bfOffBits + fi->biSizeImage;
    for (int i = 0; i < 256; i++) {
        fq[i].rgbBlue = fq[i].rgbGreen = fq[i].rgbRed = i;
    }
}

void writeBMP(FILE *fpGray, fileHeader *fh, fileInfo *fi, rgbq *fq) {
    fwrite(fh, sizeof(fileHeader), 1, fpGray);
    fwrite(fi, sizeof(fileInfo), 1, fpGray);
    fwrite(fq, sizeof(rgbq), 256, fpGray);
}

void convertToGray(FILE *fpBMP, FILE *fpGray, fileInfo *fi) {
    unsigned char rgbImgData[3];
    unsigned int grayImgData;
    unsigned char rgbAnthor;
    long oldBiWidth = getLineBytes(fi->biWidth, fi->biBitCount);
    long newBiWidth = getLineBytes(fi->biWidth, 8);
    for (int i = 0; i < fi->biHeight; i++) {
        for (int j = 0; j < newBiWidth; j++) {
            if (j < fi->biWidth)
            {
                for (int k = 0; k < 3; k++) {
                    fread(&rgbImgData[k], 1, 1, fpBMP);
                }
                grayImgData = (int)((float)rgbImgData[0] * 0.299 + (float)rgbImgData[1] * 0.587 + (float)rgbImgData[2] * 0.114);
            }
            else {
                grayImgData = 0;
            }
            fwrite(&grayImgData,1, 1, fpGray);
        }
        for (int k = fi->biWidth * 3; k < oldBiWidth; k++) {
            fread(&rgbAnthor, 1, 1, fpBMP);
        }
    }   
}

int main() {
    unsigned char bmpRGBPath[] = "test.bmp";
    unsigned char bmpGrayPath[] = "gray.bmp";
    FILE *fpBMP, *fpGray;
    fileHeader fh;
    fileInfo fi;
    rgbq fq[256];
    fpBMP = fopen(bmpRGBPath, "rb");
    fpGray = fopen(bmpGrayPath, "wb");
    readBMP(fpBMP, &fh, &fi, fq);
    writeBMP(fpGray, &fh, &fi, fq);
    convertToGray(fpBMP, fpGray, &fi);
    fclose(fpGray);
    fclose(fpBMP);
    return 0;
}

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