做“color grading"出现条纹

作业2的基础部分，自己写的代码和参考网上的其他代码都出现了条纹问题，求助！！！

附上代码：

void main()
{
    highp ivec2 lut_tex_size = textureSize(color_grading_lut_texture_sampler, 0);
    highp float _COLORS      = float(lut_tex_size.y);
    highp float width        = float(lut_tex_size.x);

    highp vec4 color       = subpassLoad(in_color).rgba;

    highp float blue         = (_COLORS - 1.0) * color.b;
    highp float red          = (_COLORS - 1.0) * color.r;
    highp float green       = (_COLORS - 1.0) * color.g;

    highp float r1 = red + floor(blue) * _COLORS;
    highp float r2 = red + ceil(blue) * _COLORS;
    //归一化
    highp float u1 = r1 / width;
    highp float u2 = r2 / width;

    highp float v = green / _COLORS;
    highp vec2 uv1 = vec2(u1,v);
    highp vec2 uv2 = vec2(u2,v);

    highp vec3 color1  =   texture(color_grading_lut_texture_sampler, uv1).xyz;
    highp vec3 color2  =   texture(color_grading_lut_texture_sampler, uv2).xyz;

    //混合
    highp vec3 mixedcolor   =   mix(color1,color2,fract(blue));
    
    out_color = vec4(mixedcolor,color.a);
}