The max function did not work? Why not? Surely you tried it?
S = rand([1,128,3],'single')
S = 1×128×3 single array
S(:,:,1) =
0.9557 0.1427 0.3405 0.6756 0.9683 0.2260 0.2643 0.8766 0.1601 0.3533 0.1217 0.5791 0.1570 0.9396 0.3561 0.3374 0.2021 0.9924 0.1874 0.1094 0.4630 0.4364 0.3554 0.9370 0.0987 0.4981 0.1302 0.0768 0.9896 0.2384 0.1609 0.2545 0.5572 0.7844 0.8800 0.6078 0.1950 0.0075 0.5522 0.8453 0.3545 0.2669 0.8706 0.4797 0.9956 0.5484 0.8204 0.8800 0.3609 0.3253 0.5001 0.0510 0.7105 0.7387 0.3200 0.9856 0.8967 0.8876 0.0119 0.7305 0.6968 0.1452 0.9469 0.0811 0.7298 0.2679 0.5191 0.2916 0.8015 0.1417 0.0169 0.7617 0.3939 0.5777 0.0981 0.5780 0.8458 0.6728 0.6075 0.0170 0.4806 0.8411 0.5548 0.5855 0.0772 0.3482 0.1833 0.3835 0.7599 0.8728 0.3124 0.5976 0.1430 0.3458 0.6698 0.9066 0.1878 0.8884 0.8400 0.3497 0.1501 0.7870 0.3385 0.6183 0.9170 0.6736 0.6312 0.3466 0.2678 0.5486 0.7385 0.8791 0.3033 0.4010 0.8053 0.1195 0.7835 0.9073 0.9074 0.5491 0.4376 0.5875 0.8007 0.5016 0.3179 0.8934 0.3880 0.8169
S(:,:,2) =
0.6750 0.0244 0.7297 0.7161 0.7345 0.3474 0.3519 0.9932 0.0022 0.5864 0.3253 0.5362 0.7495 0.2942 0.1847 0.4343 0.0366 0.6893 0.2565 0.9985 0.1643 0.4219 0.7648 0.7371 0.2732 0.6387 0.2065 0.8124 0.1072 0.3629 0.9866 0.8684 0.6886 0.7622 0.5557 0.5917 0.0315 0.2410 0.6593 0.9543 0.7830 0.0649 0.7360 0.6809 0.0108 0.3909 0.5070 0.6011 0.7611 0.3374 0.3473 0.1922 0.8107 0.5036 0.1575 0.3710 0.4097 0.7914 0.5949 0.7992 0.6088 0.0735 0.7162 0.6951 0.6174 0.0584 0.1226 0.9477 0.2845 0.3434 0.7580 0.7480 0.7757 0.7594 0.5944 0.2847 0.4666 0.2775 0.4339 0.0988 0.6698 0.0340 0.6814 0.6940 0.9222 0.1348 0.2211 0.8204 0.3004 0.6479 0.4911 0.9741 0.9958 0.2539 0.9974 0.3831 0.5335 0.0473 0.9102 0.7727 0.5120 0.8768 0.2086 0.8226 0.4095 0.4167 0.7353 0.1733 0.8169 0.5070 0.2328 0.2235 0.4618 0.0158 0.1165 0.4908 0.7861 0.4782 0.6259 0.3511 0.7469 0.7876 0.7971 0.5446 0.2603 0.1840 0.6295 0.9905
S(:,:,3) =
0.4791 0.2940 0.6249 0.2390 0.0943 0.6676 0.3252 0.6926 0.2384 0.1067 0.8984 0.4460 0.0757 0.2423 0.4307 0.2851 0.2647 0.1595 0.0255 0.9026 0.6795 0.9780 0.7197 0.1265 0.1647 0.7993 0.6764 0.8225 0.9037 0.2253 0.2844 0.4565 0.2419 0.0760 0.8307 0.6283 0.8663 0.2074 0.8725 0.5262 0.3077 0.7511 0.6912 0.9238 0.1845 0.0062 0.9845 0.0728 0.5196 0.6840 0.5730 0.9710 0.1344 0.8643 0.8640 0.6774 0.0758 0.9000 0.1705 0.0219 0.8878 0.3826 0.9206 0.2563 0.6831 0.7040 0.0375 0.0802 0.7031 0.1078 0.7203 0.7382 0.4817 0.8284 0.8753 0.5169 0.1553 0.8930 0.8759 0.9566 0.7253 0.1547 0.8878 0.7939 0.9599 0.1355 0.5782 0.1458 0.3618 0.6818 0.3221 0.1438 0.7235 0.8641 0.4978 0.1295 0.8315 0.2729 0.4741 0.1573 0.9220 0.3514 0.3494 0.2594 0.7933 0.1565 0.6889 0.9444 0.4240 0.5562 0.2459 0.2756 0.4601 0.2840 0.9458 0.4839 0.6426 0.0580 0.7558 0.0852 0.7317 0.1730 0.2258 0.4086 0.4143 0.8189 0.0147 0.2181
Smax = max(S,[],2)
Smax = 1×1×3 single array
Smax(:,:,1) =
0.9956
Smax(:,:,2) =
0.9985
Smax(:,:,3) =
0.9845
If you don't like that the result is now 1x1x3, use squeeze, or reshape to put it in the shape you prefer.
squeeze(Smax)
ans = 3×1
0.9956
0.9985
0.9845
Actually, a simple max(S) would also have worked, since max will apply to the first non-singleton dimension.
max(S)
ans = 1×1×3 single array
ans(:,:,1) =
0.9956
ans(:,:,2) =
0.9985
ans(:,:,3) =
0.9845
So all you had to do was try the max function.