difference of gaussian

we don't need to filter twice !

as it turns out, we can just subtract the kernels

[0.2353390554756015, 0.529321889048797, 0.2353390554756015][1 x 3]
[0.3231807690118479, 0.3536384619763042, 0.3231807690118479]
[3.57151, 4.201, 4.03934, 0]
[491.91342, 456.77701, 368.935, 87.841797, 140.54671, -9.5367432e-05, -210.8201, -228.3884, -263.52512, -228.3884, -228.3884, -193.2518, -597.32379, -579.75537, -632.46039;
 -17.568207, -35.136604, -228.3884, -491.9137, -474.34521, -597.32361, -175.6835, -122.9784, -210.8201, 456.77701, 509.48218, 439.20862, 35.136604, 52.705002, 0;
 948.69043, 983.82703, 1018.9638, -421.6402, -368.93512, -386.5036, 281.0936, 333.79849, 333.79858, 263.52502, 298.6618, 281.0932, -105.41, -158.1152, -122.97821;
 -527.05029, -527.05023, -527.05023, -35.136604, -105.41019, -105.41019, 105.41, 140.54671, 105.41, 140.5468, 105.41, 122.9784, 210.82019, 175.68359, 122.97821;
 -1089.2372, -1071.6689, -825.71204, 667.59698, 720.302, 948.69061, -597.32361, -632.46033, -509.48181, 17.568398, 17.568398, 17.568398, -35.136795, -35.136604, 52.705383]
[491.91589, 456.78101, 368.93616, 87.841797, 140.54871, 0, -210.81924, -228.38745, -263.52386, -228.38898, -228.38898, -193.25256, -597.32208, -579.75159, -632.4585;
 -17.565918, -35.137939, -228.38745, -491.91284, -474.3454, -597.32288, -175.68359, -122.97668, -210.82153, 456.7749, 509.48181, 439.21204, 35.137939, 52.706909, 0.0030517578;
 948.6908, 983.82874, 1018.9636, -421.64001, -368.93463, -386.5036, 281.09283, 333.80127, 333.79974, 263.52539, 298.66333, 281.09131, -105.41077, -158.11462, -122.97668;
 -527.05078, -527.05078, -527.04773, -35.136414, -105.40924, -105.41077, 105.41077, 140.54871, 105.40924, 140.54871, 105.41077, 122.97974, 210.82153, 175.68359, 122.97974;
 -1089.2349, -1071.6675, -825.71106, 667.59796, 720.30182, 948.6908, -597.32208, -632.45923, -509.48029, 17.56897, 17.56897, 17.56897, -35.137939, -35.137939, 52.706909]