Better understanding of STAR statistical summary

Question

[mohsamir2016]

Dear experts,

I would like to understand better the output of STAR log.final file alongside with samtools output: I run STAR command without including --outSAMunmapped Within and without outFilterMultimapNmax nor outFilterMismatchNmax , so this is default STAR:

I got statistics summary from the log.final file. my questions are:

1. Are the number of input reads is exactly the same as the one that I have from trimmed versions of R1 and R2 summed up or?
2. What exactly the Uniquely mapped reads number ? is that the n of reads that map to only 1 position on the genome OR that map to < 10 position OR the reads that do not have any other similar reads mapping to the position on the genome?
3. Does the Uniquely mapped reads number include the multimapped reads that mapped tp < 10 position (so basically include the 'Number of reads mapped to multiple loci' appeared on statistics summary ?
4. What does the reads with 255 mapping Q means? are these are the ones that map to only 1 place on the genome ? so should be equal to the number of Uniquely mapped reads number if it means mapped to 1 position (I tried that they are not the same? OR they are similar to the Uniquely mapped reads number if I set the outFilterMultimapNmax to 1 ?

Please could someone expert in STAR put an end to my confusion by elaboratively help me understating these points ?

Thanks