I want to threshold values greater than 15 using AVX2 instructions but it compares only signed numbers.

    __m256i *pIn0, *pIn1,*pOut;
    __m256i a, b, thres = _mm256_set1_epi8(15); //Threshold value is set to 15
    
    for (int i = 0; i < nHeight; i++)
    {
        pIn0 = (__m256i*)(pY1 + i * nStepSize); //buffer 1 having 8 bit unsigned integers
        pIn1 = (__m256i*)(pY2 + i * nStepSize); //buffer 2 having 8 bit unsigned integers
        pOut = (__m256i*)(pdiffAnd + i * nStepSize);

        int wLimit = nWidth / 32;
        for (int j = 0; j < wLimit; j++)
        {
            a = _mm256_lddqu_si256(pIn0++); //32 values of UINT8 type
            b = _mm256_lddqu_si256(pIn1++); //32 values of UINT8 type


            __m256i diff1 = _mm256_or_si256(_mm256_subs_epu8(a, b), _mm256_subs_epu8(b, a)); //taking their absolute difference

      /* here _mm256_cmpgt_epi8 is comparing values assuming 8 bit Signed integers so values greater than 127 are not getting compared */
            __m256i diff1Mask = _mm256_cmpgt_epi8(diff1, thres);

            __m256i blend1 = _mm256_blendv_epi8(diff1, diff1Mask, diff1Mask);

            _mm256_store_si256(pOut++, blend1);
        }
    }

I thought a solution to find all values less than 0 and perform bitwise OR with diff1Mask but also got stuck to find values less than 0.

PS: I’m a newbie