一：通过文字生成图片

// 通过文字生成图片
+ (UIImage *)imageWithTextStr:(NSString *)string font:(UIFont *)font width:(CGFloat)width textAlignment:(NSTextAlignment)textAlignment {
    NSDictionary *attributeDic = @{NSFontAttributeName:font};
    CGSize size = [string boundingRectWithSize:CGSizeMake(width, 10000)
                                       options:NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingTruncatesLastVisibleLine
                                    attributes:attributeDic
                                       context:nil].size;
    NSInteger retWidth = ceil(size.width);
    NSInteger retHeight = ceil(size.height);
    if (retWidth % 2 != 0) {
        retWidth++;
    }
    if (retHeight % 2 != 0) {
        retHeight++;
    }
    size = CGSizeMake(retWidth, retHeight);
    if ([UIScreen.mainScreen respondsToSelector:@selector(scale)]) {
        if (UIScreen.mainScreen.scale == 2.0) {
            UIGraphicsBeginImageContextWithOptions(size, NO, 1.0);
        } else {
            UIGraphicsBeginImageContext(size);
        }
    } else {
        UIGraphicsBeginImageContext(size);
    }
    CGContextRef context = UIGraphicsGetCurrentContext();
    [[UIColor colorWithWhite:0 alpha:0] set];
    
    CGRect rect = CGRectMake(0, 0, retWidth, retHeight);
    CGContextFillRect(context, rect);
    NSMutableParagraphStyle *paragraph = [[NSMutableParagraphStyle alloc] init];
    paragraph.alignment = textAlignment;
    NSDictionary *attributes = @{
                                 NSForegroundColorAttributeName:[UIColor whiteColor],
                                 NSFontAttributeName:font,
                                 NSParagraphStyleAttributeName:paragraph
                                 };
    [string drawInRect:rect withAttributes:attributes];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

二：图片转为RGB

+ (unsigned char *)rgbDataWithImage:(UIImage *)img {
    CGImageRef imgRef = [img CGImage];
    CGSize size = img.size;
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    int pixelCount = size.width * size.height;
    uint8_t* rgba = (uint8_t*)malloc(pixelCount * 4);
    CGContextRef context = CGBitmapContextCreate(rgba, size.width, size.height, 8, 4 * size.width, colorSpace, kCGImageAlphaPremultipliedLast);
    CGColorSpaceRelease(colorSpace);
    CGContextDrawImage(context, CGRectMake(0, 0, size.width, size.height), imgRef);
    CGContextRelease(context);
    uint8_t *rgb = (uint8_t*)malloc(pixelCount * 3);
    int m = 0;
    int n = 0;
    /** 移除掉Alpha */
    for(int i=0; i<pixelCount; i++){
        rgb[m++] = rgba[n++];
        rgb[m++] = rgba[n++];
        rgb[m++] = rgba[n++];
        n++;
    }
    free(rgba);
    return rgb;
}