DagNN Why adding convolution layer reduces the intensity of the output values?

I'm trying to estimate density map using Deep learning Architecture with DagNN (MatConvnet). I've seen output abruptly reduce in intensity after passing the convolution layer. I tried using LRN normalization to enhance the output- however the running error and objective resulted in 'NaN' or 'Inf'.

The conv layer is defined as:

net.addLayer('conv5', dagnn.Conv('size', [1,1,8,1], 'hasBias', true, 'stride', [1, 1], 'pad', [1 1 1 1]), {'lrn4'}, {'prediction'},  {'conv5f'  'conv5b'});
net.params(9).value=  0.1*scal*randn(1,1,8,1, 'single');
net.params(10).value= 0.001*init_bias*ones(1, 1, 'single');%'biases',
net.params(9).learningRate=1;net.params(9).weightDecay=1;
net.params(10).learningRate=2;net.params(10).weightDecay=0;