Computing block sum for an arbitrary region in an image - algorithm

I wonder what is the most effective way to solve the following problem:
(If there is a name for this problem, I would like to know it as well)
[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 1 0 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 1 0 0 1 0 1 1 1;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 1 1 1 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0;
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]
If I have an image where I am interested in the following pixels marked by 1. In an image I want to calculate a sum around this block. A sum of block is easy to calculate from an integral image but I don't want to do it for the whole image, since there is a lot of unnecessary computation.
One option that I can come up with is to search the minimum and maximum in horizontal and vertical directions and then take a rectangular portion of the image enlarged so that it will covered the block portion. For example +2 pixels each directions, if the block size is 5. But this solution still includes unnecessary calculation.
If I had a list of these indices, I could loop through them and calculate the sum for each block but then if there is another pixel close by which has the same pixels in its block, I need to recalculate them and If I save them, I somehow need to look if they are already calculated or not and that takes time as well.
Is there a known solution for this sort of a problem?

Related

Go DNS trouble with TCP transport fine with UDP

I've tried everything I can think of and I'm hitting a brick wall. I wonder if anyone is able to point me in the right direction or possibly spot the issue?
I'm having a go at writing my own DNS server for a couple of reasons, the main a learning experience.
A few things to mention:
I'm using Go
Using "gopacket" for the DNS packet de/serialisation
The server works as expected when using the UDP protocol
So after getting responses over UDP working I decided it was time to implement TCP. Below is a snippet of the code listening for the TCP incoming connections.
// Listen TCP
c, err := t.Accept()
if err != nil {
log.Println(err)
}
go func(c net.Conn) {
tbuff := make([]byte, 4096)
_, err = c.Read(tbuff)
if err != nil {
fmt.Println(err)
}
clientAddr := addrt
packet := gopacket.NewPacket(tbuff, layers.LayerTypeDNS, gopacket.Default)
dnsPacket := packet.Layer(layers.LayerTypeDNS)
tcp, _ := dnsPacket.(*layers.DNS)
if !limiter(clientAddr.String()) {
c.Close()
}
tbuff = DNSHandle(tcp)
c.Write(tbuff)
c.Close()
}(c)
When I issue a dig command over TCP the server accepts the connection and passed the received byte data to the DNSHandle function (same as the UDP handler). The data seems to be very different of that when using UDP.
UDP request after gopacket deserialisation:
&{{[91 174 1 32 0 1 0 0 0 0 0 1 11 116 101 115 116 101 120 97 109 112 108 101 3 99 111 109 0 0 1 0 1 0 0 41 16 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 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0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0] []} 23470 false Query false false true false 2 No Error 1 0 0 1 [{[116 101 115 116 101 120 97 109 112 108 101 46 99 111 109] A IN}] [] [] [{[] OPT Unknown 0 0 [] <nil> [] [] [] [] {[] [] 0 0 0 0 0} {0 0 0 []} {0 []} [] {0 0 []} []}] [46 116 101 115 116 101 120 97 109 112 108 101 46 99 111 109]}
TCP request after gopacket deserialisation:
<nil>
However if I change tbuff to [2:]:
packet := gopacket.NewPacket(tbuff[2:], layers.LayerTypeDNS, gopacket.Default)
It passes the request but malformed (which I suppose you'd expect):
&{{[114 11 1 32 0 1 0 0 0 0 0 1 11 116 101 115 116 101 120 97 109 112 108 101 3 99 111 109 0 0 1 0 1 0 0 41 16 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 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0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0] []} 29195 false Query false false true false 2 No Error 1 0 0 1 [{[116 101 115 116 101 120 97 109 112 108 101 46 99 111 109] A IN}] [] [] [{[] OPT Unknown 0 0 [] <nil> [] [] [] [] {[] [] 0 0 0 0 0} {0 0 0 []} {0 []} [] {0 0 []} []}] [46 116 101 115 116 101 120 97 109 112 108 101 46 99 111 109]}
I appreciate this may be a long shot but any help would be very welcome.
EDIT:
Thank you to both #Steffen Ullrich, #selbie. I've managed to get my code working. It's not pretty and needs a lot more work but here is a POC snippet:
// Listen TCP
c, err := t.Accept()
if err != nil {
log.Println(err)
}
go func(c net.Conn) {
tbuff := make([]byte, 4096)
msize := make([]byte, 2)
size, err := c.Read(tbuff)
if err != nil {
fmt.Println(err)
}
DNSMsgLength := binary.BigEndian.Uint16(tbuff[:2])
if int(DNSMsgLength) == size-2 {
fmt.Println("Size correct")
}
clientAddr := addrt
packet := gopacket.NewPacket(tbuff[2:], layers.LayerTypeDNS, gopacket.Default)
dnsPacket := packet.Layer(layers.LayerTypeDNS)
tcp, _ := dnsPacket.(*layers.DNS)
if !limiter(clientAddr.String()) {
c.Close()
}
tbuff = DNSHandle(tcp)
binary.BigEndian.PutUint16(msize, uint16(len(tbuff)))
tbuff = append(msize, tbuff...)
c.Write(tbuff)
c.Close()
}(c)

However if I change tbuff to [2:]:
From RFC 1035 section 4.2.2:
4.2.2. TCP usage
Messages sent over TCP connections use server port 53 (decimal). The
message is prefixed with a two byte length field which gives the message
length, excluding the two byte length field. This length field allows
the low-level processing to assemble a complete message before beginning
to parse it.
Thus by treating DNS over TCP the same as DNS over UDP you are doing it wrong - in TCP a DNS message is prefixed with 2 bytes containing the length of the message.
This is needed since TCP is a byte stream and not a datagram protocol like UDP. This means that one cannot simply assume that exactly a single and full DNS message will be returned by c.Read(...). It might be possible that not the full message was received yet but also that more than one DNS message was received. Check the length prefix for this.

Find 4-neighbors using J

I'm trying to find the 4-neighbors of all 1's in a matrix of 0's and 1's using the J programming language. I have a method worked out, but am trying to find a method that is more compact.
To illustrate, let's say I have the matrix M—
] M=. 4 4$0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0
0 0 0 0
0 0 1 0
0 0 0 0
0 0 0 0
and I want to generate—
0 0 1 0
0 1 0 1
0 0 1 0
0 0 0 0
I've sorted something close (which I owe to this little gem: https://www.reddit.com/r/cellular_automata/comments/9kw21u/i_made_a_34byte_implementation_of_conways_game_of/)—
] +/+/(|:i:1*(2 2)$1 0 0 1)&|.M
0 0 1 0
0 1 2 1
0 0 1 0
0 0 0 0
which is fine because I'll be weighting the initial 1's anyway (and the actual numbers aren't really that important for my application anyway). But I feel like this could be more compact and I've just hit a wall. And the compactness of the expression actually is important to my application.

Building on #Eelvex comment solution, if you are willing to make the verb dyadic it becomes pretty simple. The left argument can be the rotation matrix and then the result is composed with +./ which is a logical or and can be weighted however you want.
] M0=. 4 4$0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0
0 0 0 0
0 0 1 0
0 0 0 0
0 0 0 0
] m =.2,\5$0,i:1
0 _1
_1 0
0 1
1 0
m +./#:|. M0
0 0 1 0
0 1 0 1
0 0 1 0
0 0 0 0
There is still an issue with the edges (which wrap) around, but that also occurs with your original solution, so I am hoping that you are not concerned with that.
] M1=. 4 4$1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
m +./#:|. M1
0 1 0 1
1 0 0 0
0 0 0 0
1 0 0 0
If you did want to clean that up, you can use the slightly longer m +./#:(|.!.0), which fills the rotation with 0's.
] M2=. 4 4$ 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 1
m +./#:(|.!.0) M2
0 0 0 0
0 0 0 0
0 0 0 1
0 0 1 0
m +./#:(|.!.0) M1
0 1 0 0
1 0 0 0
0 0 0 0
0 0 0 0

problem with extract region pixels from gray image on Matlab

I would to like to selection the dark gray pixels from gray image.
J = rgb2gray(I);
Newfigure = zeros(size(J));
[k,l] =find(J<130);
Newfigure(k,l) = J(k,l);
imshow(Newfigure)
when visualize the Newfigure, I see the zone of circle like square. Why does this happen?

This is due to the way you index into Newfigure. Look at the following:
>> test = zeros(10);
>> test([2,8], [1,2]) = 1
test =
0 0 0 0 0 0 0 0 0 0
1 1 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
1 1 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
This is different from
>> test = zeros(10);
>> test(2, 1) = 1;
>> test(8, 2) = 1
test =
0 0 0 0 0 0 0 0 0 0
1 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 1 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
You could either use a loop like
Newfigure = zeros(size(J));
for n = 1:numel(k);
Newfigure(k(n), l(n)) = J(k(n), l(n));
end
or simply use
Newfigure = J < 130;
imshow(Newfigure);

Get rid of the find(...) and just use logical indices. It'll be faster too...
J = rgb2gray(I);
Newfigure = zeros(size(J));
tf = J<130;
Newfigure(tf) = J(tf);
imshow(Newfigure)
The tf variable will be an array of 0s/1s (true/false), the same size as J which you can then use to index the arrays as shown.

Interpreting memory usage of game in Go

I have added memory profiling to my game and when taking a look to the stats I can see something like this :
# runtime.MemStats
# Alloc = 1022232
# TotalAlloc = 14369528
# Sys = 72286456
# Lookups = 0
# Mallocs = 192759
# Frees = 184964
# HeapAlloc = 1022232
# HeapSys = 66519040
# HeapIdle = 64667648
# HeapInuse = 1851392
# HeapReleased = 61906944
# HeapObjects = 7795
# Stack = 589824 / 589824
# MSpan = 29920 / 65536
# MCache = 6944 / 16384
# BuckHashSys = 1444778
# GCSys = 2377728
# OtherSys = 1273166
# NextGC = 4194304
# LastGC = 1571576758413809106
# PauseNs = [136190 27071 23449 40823 35342 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]
# PauseEnd = [1571576480170696886 1571576526952274688 1571576646967831188 1571576688475083354 1571576758413809106 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]
# NumGC = 5
# NumForcedGC = 0
# GCCPUFraction = 2.6422038270754447e-06
# DebugGC = false
I believe I am having memory leaks but I am having a hard time pinpointing the exact code doing it. I believe I have leaks because I can "pause" the game and when I do I basically just continue in the game loop but I dont do anything ( I dont draw on the screen or create new objects ) but I can see the field TotalAlloc keeps growing and growing forever, so I assume something definitely must be wrong right?
Here is my code : https://github.com/Matias-Barrios/SDL_Universe/blob/master/main.go

Gnuplot set matrix dimension

I have a datafile contains two 101*101 matrix of float numbers, one is data and the other is error.
It looks like this
0 0 0 0 0 0 0
0 0 0 0 0 0 0
0 0 0 0 0 0 0
10381.8 0 0 3462.03 10341 0 6889.64
6919.26 6916.64 3459.49 10349.8 13781.3 6887.57 24157.2
3459.66 0 24158.9 13792.6 3433.65 27579.4 24117.4
0 0 0 0 0 0 0
0 0 0 0 0 0 0
# Errors [Positon_sample/samp_psd.txt] I_err:
0 0 0 0 0 0 0
0 0 0 0 0 0 0
0 0 0 0 0 0 0
4892.66 4890.8 3459.49 5975.49 6890.64 4870.25 9130.63
3459.66 0 9131.25 6896.32 3433.65 9750.84 9115.54
3464.99 4888.97 5972.77 11419.1 7713.44 8438.29 9093.38
0 0 0 0 0 0 0
0 0 0 0 0 0 0
Now I would like to only plot the first matrix.
I use "plot 'E:\samp_psd.txt' matrix with image"
But the program corrupt...
It seems that I should set the dimension of the matrix,
My case is a little similar like this
Gnuplot plot Matrix over Matrix

I would separate the two matrices with two empty lines like this:
0 0 0 0 0 0 0
0 0 0 0 0 0 0
0 0 0 0 0 0 0
10381.8 0 0 3462.03 10341 0 6889.64
6919.26 6916.64 3459.49 10349.8 13781.3 6887.57 24157.2
3459.66 0 24158.9 13792.6 3433.65 27579.4 24117.4
0 0 0 0 0 0 0
0 0 0 0 0 0 0
# Errors [Positon_sample/samp_psd.txt] I_err:
0 0 0 0 0 0 0
0 0 0 0 0 0 0
0 0 0 0 0 0 0
4892.66 4890.8 3459.49 5975.49 6890.64 4870.25 9130.63
3459.66 0 9131.25 6896.32 3433.65 9750.84 9115.54
3464.99 4888.97 5972.77 11419.1 7713.44 8438.29 9093.38
0 0 0 0 0 0 0
0 0 0 0 0 0 0
Then you can access a single matrix with the index command like this:
plot "samp_psd.txt" index 0 matrix with image

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