Develop Reference

JFIF and EXIF data structures

I'm creating a program which reads and prints out metadata from an image, but I'm struggling to get my head around the JFIF and EXIF marker structures.
According to the wikipedia page for JFIF, the JFIF marker should be as follows:
FF E0 s1 s2 4A 46 49 46 00 ii ii jj XX XX YY YY xx yy
Where:
FF E0 is the start of the JFIF marker
s1 and s2 combined give the size of the segment (excluding the APP0 marker)
4A 46 49 46 00 is the identifier (literally JFIF in ascii)
i is the version of JFIF (2 bytes)
j is the density uni for DPI measurement
X is the Horizontal DPI
Y is the Vertical DPI
x is the Horizontal THUMBNAIL DPI
y is the Vertical THUMBNAIL DPI
However, when running an image through my program, I get this:
ff e0 20 10 4a 46 49 46 20 1 1 20 20 48 20 48 20 20 ff e1
The marker start is there, but the segment size looks well off (0x2010??) seeing as the next Marker for EXIF data starts just 15 bytes later! (FF E1)
I think that hex values of 0x00 aren't being printed (hence why my image prints the JFIF identifier without the zeros) which may be adding to the confusion, but even then, how is the JFIF version 20 20?
If anyone on here has any experience looking at image metadata, I'd really appreciate your help! There's not a lot of resources that I can find that break down JFIF/EXIF data very clearly.
If you need me to post any code in here then I can, though apart from not printing 0x00 values to the console, it seems to being working as expected, so I think my main issue is actually understanding the meta data
Here is the code for taking the byte stream and then converting it into hex:
fileLocation = Console.ReadLine();
var fileDataAsBytes = File.ReadAllBytes(fileLocation);
var headers = fileDataAsBytes
.Select((b, i) => (b, i))
.Where(tuple => tuple.b == 0xFF
&& fileDataAsBytes[tuple.i + 1] == 0xE1)
.Select(tuple => $"{tuple.i}: {tuple.b:x}
{fileDataAsBytes[tuple.i + 1]:x}");
Console.WriteLine(String.Join(",", headers));
DealWithMarkers(fileDataAsBytes);
DisplayAllConversions(fileDataAsBytes);
public static void DisplayAllConversions(byte[] fileDataAsBytes)
{
DisplayBytes(fileDataAsBytes);
DisplayHex(fileDataAsBytes);
DisplayString(fileDataAsBytes);
}
public static void DisplayHex(byte[] fileDataAsBytes)
{
Console.WriteLine($"\n\n\n\t*\t*\t*\t(As Hex)\t*\t*\t*\n");
for (int i = 0; (i < 1000) && (i < fileDataAsBytes.Length); i++)
{
Console.Write($"{fileDataAsBytes[i]:x} ");
}
}
I tried this with a different image and it actually prints out the 0 value bytes correctly, so there must be something weird with the image file I was analyzing!
Image file with "incorrect" 0 bytes
Image file with "correct" 0 bytes

What kind of Algorithm am I looking for to combine quantities?

I have been stuck on this problem now for 8 weeks and I think that I almost have a solution however the last bit of math is racking my mind. I will try to explain a simple problem that requires a complex solution. I am programing in C#.net MVC Web Project. Here is the situation.
I have an unknown group of quantities incoming to look for like items. Those like items share a max level to make it a full box. Here is an example of this:
Revision******
This is the real world case
I have many, let say candy, orders coming in to a company.
Qty Item MaxFill Sold-To DeliverNumber
60 candy#14 26 Joe 1
1 candy#12 48 Jim 2
30 candy#11 48 Jo 3
60 candy#15 48 Tom 4
6 candy#8 48 Kat 5
30 candy#61 48 Kim 6
44 candy#12 48 Jan 7
10 candy#12 48 Yai 8
10 candy#91 48 Jun 9
55 candy#14 26 Qin 10
30 candy#14 26 Yo 11
40 candy#14 26 Moe 12
in this list I am looking for like candy items to combine to make all the full boxes of candy that I can based off the MaxFill number. Here we see the like items are:
Qty Item MaxFill Sold-To DeliverNumber
60 candy#14 26 Joe 1
55 candy#14 26 Qin 10
30 candy#14 26 Yo 11
40 candy#14 26 Moe 12
1 candy#12 48 Jim 2
44 candy#12 48 Jan 7
10 candy#12 48 Yai 8
Now lets take the first set of numbers for candy#14.
I know that the total of candy#14 is 185 and I can get 7 full boxes of 26 with one box having only 3 in the last box. So how do I do this with the values that I have without losing the information of the original order. So this is how I am working it out right now
See below
End of Revision******
Like candy#14 max fill level is 26.
Like candy#14 quantities:
60
55
30
40
Now I already have a recursive function to break these down to the 26 level and is working fine. I feel that I need another recursive function to deal with the remainders that come out of this. As you can see most of the time there will be remainders from any given list but those remainders could total up to another full box of 26.
60 = 26+26+8
55 = 26+26+3
30 = 26+4
40 = 26+14
The 8,3,4,14 = 29 so I can get another 26 out of this. But in the real unknown world I could have the remainders come up with a new set of remainders that could repeat the same situation. To make this even more complicated I have to save the data that is originality with the 60,55,30,40 that is carried with it such as who it was sold to and delivery number. This will also be helpful with knowing how the original amount was broken down and combined together.
from the 8,3,4,14 the best way that I was think to add to that value is to take the 8,4,14 this will give me the 26 that I am looking for and I would not have to split any value because 3 is the remainder and I could save all other data without issue. However this just works in this situation only. If I go in a linear motion 8+3+4=15 so I would have to take 11 from the next value 14 with a remainder of 3.
In reading about different algorithms I was thinking that this might fall into the NP,NP-Complete,NP-Hard category. But with all the situations it is very technical and not a lot of real world scenarios are to be found.
Any suggestions would help here if I should go through the list of number to find the best combinations to reach the 26 or if the linear progression and splitting of the next value is the best solution. I know that I can solve to get how many full boxes I could get from the remainders and what the left over amount would be such as 8+3+4+14=29 which would give me 1, 26 and 1, 3 but I have no idea about the math in a recursive way to solve this. I have this much done and I "feel" that this is on the right track but can't see how to adjust to make this work with the linear or "test every possible combination".
public static void Main(string[] args)
{
var numbers = new List<int>() { 8, 3, 4, 14 };
var target = 26;
sum_up(numbers, target);
}
private static void sum_up(List<int> numbers, int target)
{
sum_up_recursive(numbers, target, new List<int>());
}
private static void sum_up_recursive(List<int> numbers, int target, List<int> partial)
{
int s = 0;
foreach (int x in partial) s += x;
if (s == target)
{
var outputtext = "sum(" + string.Join(",", partial.ToArray()) + ")=" + target;
}
if (s >= target)
return;
for (int i = 0; i < numbers.Count; i++)
{
List<int> remaining = new List<int>();
int n = numbers[i];
for (int j = i + 1; j < numbers.Count; j++) remaining.Add(numbers[j]);
List<int> partial_rec = new List<int>(partial);
partial_rec.Add(n);
sum_up_recursive(remaining, target, partial_rec);
}
}

I wrote sample project in javascript.
Please check my repo.
https://github.com/panghea/packaging_sample

C# Translating a few smaller arrays to one big

Title may not explain fully what I want to do, so I made an image.
You can see there are 4 1D arrays(red numbers, black colored numbers are indexes), each of this array goes from 0 to 63. I want to somehow translate them, that for example, index 16 will point to first index of second array.
What I was thinking of, is a function where I give List of arrays and index that I want to get as input, and its returns me the index of array and exact index in this array as output.
I would like to have some hints or suggestions on how to proceed here to achieve this functionality.

Ok, your image shows an interleaved data of 16 elements, so you want to have (showing an example of only two matrices because of space :D)
Global index
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
-----------------------------------------------------------------------------------------------------
Array0 indexes - Array1 indexes
0 1 2 3 4 5 6 7 8 9 A B C D E F - 0 1 2 3 4 5 6 7 8 9 A B C D E F
-------------------------------------------------------------------------------------------------
Global index
33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
-----------------------------------------------------------------------------------------------------
Array0 indexes - Array1 indexes
10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F - 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F
To get it you can do something like this:
public class CompositeIndex
{
public int ArrayNumber { get; set; }
public int ElementNumber { get; set; }
}
public static CompositeIndex GetIndex(int GlobalIndex, int ArrayCount, int ElementsToInterleave)
{
CompositeIndex index = new CompositeIndex();
int fullArrays = GlobalIndex / ElementsToInterleave; //In your example: 16 / 16 = 1;
index.ArrayNumber = fullArrays % ArrayCount; //In your example: 1 mod 4 = 1;
index.ElementNumber = GlobalIndex - (fullArrays * ElementsToInterleave); //In your example: 16 - (1 * 16) = 0;
return index;
}
Then, if you have 4 matrices and want to get the "global" index 16 you do:
var index = GetIndex(16, 4, 16);
This function allows you to use an indeterminated number of arrays and interleaved elements.
BTW, another time ask better your question, a lot more people will help you if they don't have to solve a puzzles to understand what you want...

Firmata over nRF24

I'm having some technical problems... I'm trying to use Firmata for arduino but over nrf24, not over Serial interface. I have tested nRF24 communication and it's fine. I have also tested Firmata over Serial and it works.
Base device is simple "serial relay". When it has data available on Serial, read it and send it over nRF24 network. If there is data available from network, read it and send it through Serial.
Node device is a bit complex. It has custom Standard Firmata where I have just added write and read override.
Read override id handeled in loop method in this way:
while(Firmata.available())
Firmata.processInput();
// Handle network data and send it to Firmata process method
while(network.available()) {
RF24NetworkHeader header;
uint8_t data;
network.read(header, &data, sizeof(uint8_t));
Serial.print(data, DEC); Serial.print(" ");
Firmata.processInputOverride(data);
BlinkOnBoard(50);
}
currentMillis = millis();
Firmata processInputOverrride is little changed method of processInput where processInput reads data directly from FirmataSerial, and in this method we pass data down to method from network. This was tested and it should work fine.
Write method is overloaded in a different way. In Firmata.cpp I have added an method pointer that can be set to a custom method and used to send data using that custom method. I have then added custom method call after each of the FirmataSerial.write() call:
Firmata.h
...
size_t (*firmataSerialWriteOverride)(uint8_t);
...
void FirmataClass::printVersion(void) {
FirmataSerial.write(REPORT_VERSION);
FirmataSerial.write(FIRMATA_MAJOR_VERSION);
FirmataSerial.write(FIRMATA_MINOR_VERSION);
Firmata.firmataSerialWriteOverride(REPORT_VERSION);
Firmata.firmataSerialWriteOverride(FIRMATA_MAJOR_VERSION);
Firmata.firmataSerialWriteOverride(FIRMATA_MINOR_VERSION);
}
I have then set the overrided write method to a custom method that just writes byte to network instead of Serial.
size_t ssignal(uint8_t data) {
RF24NetworkHeader header(BaseDevice);
network.write(header, &data, sizeof(uint8_t));
}
void setup() {
...
Firmata.firmataSerialWriteOverride = ssignal;
...
}
Everything seems to be working fine, it's just that some data seems to be inverted or something. I'm using sharpduino (C#) to do some simple digital pin toggle. Here's how output looks like: (< came from BASE, > sent to BASE)
> 208 0
> 209 0
...
> 223 0
> 249
< 4 2 249
and here communication stops...
That last line came inverted. So i tough that I only need to invert received bytes. And it worked for that first command. But then something happens and communication stops again.
> 208 0
> 209 0
...
> 223 0
> 249 // Report firmware version request
< 249 2 4
> 240 121 247 // 240 is sysex begin and 247 is systex end
< 240 121
< 101 0 67 0 0 1 69 0 118
< 117 0 115 0
< 0 70 0 105 0 116 0 111 0 109
< 0 97 0
< 0 109
< 116 0 97 0 247
> 240 107 247
So what could be the problem here? It seems that communication with Firmata works but something isn't right...
-- EDIT --
I solved that issue. The problem was that I didn't see Serial.write() calls in sysex callback. Now that that is solved, I came up to another problem... All stages pass right (I guess) and then I dont get any response from Node when I request pin states
...
< f0 6a 7f 7f 7f ... 7f 0 1 2 3 4 5 6 7 8 9 a b c d e f f7 // analog mapping
> f0 6d 0 f7 // sysex request pin 0 state and value
> f0 6d 1 f7
> f0 6d 2 f7
...
> f0 6d 45 f7
// And I wait for response...
There is no response. Any ideas why would that happen? Node receive all messages correctly and code for handling pin states exist.

Generics Node declaration

Microsoft gives this as an Bubble sort example for learning generics. It makes sense until I get to lines 76 and 77. How are those declarations possible? Node is a class. Don't you have to instantiate it with new?
How would you optimize the sort? Which is part is generic and which is non-generic?
1 public class GenericList<T> : System.Collections.Generic.IEnumerable<T>
2 {
3 protected Node head;
4 protected Node current = null;
5
6 // Nested class is also generic on T
7 protected class Node
8 {
9 public Node next;
10 private T data; //T as private member datatype
11
12 public Node(T t) //T used in non-generic constructor
13 {
14 next = null;
15 data = t;
16 }
17
18 public Node Next
19 {
20 get { return next; }
21 set { next = value; }
22 }
23
24 public T Data //T as return type of property
25 {
26 get { return data; }
27 set { data = value; }
28 }
29 }
30
31 public GenericList() //constructor
32 {
33 head = null;
34 }
35
36 public void AddHead(T t) //T as method parameter type
37 {
38 Node n = new Node(t);
39 n.Next = head;
40 head = n;
41 }
42
43 // Implementation of the iterator
44 public System.Collections.Generic.IEnumerator<T> GetEnumerator()
45 {
46 Node current = head;
47 while (current != null)
48 {
49 yield return current.Data;
50 current = current.Next;
51
52 }
53 }
54
55 System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
56 {
57 return GetEnumerator();
58 }
59 }
60
61 public class SortedList<T> : GenericList<T> where T : System.IComparable<T>
62 {
63 // A simple, unoptimized sort algorithm that
64 // orders list elements from lowest to highest:
65
66 public void BubbleSort()
67 {
68 if (null == head || null == head.Next)
69 {
70 return;
71 }
72 bool swapped;
73
74 do
75 {
76 Node previous = null;
77 Node current = head;
78
79
80 //Console.WriteLine(previous.GetType());
81 //Console.ReadLine();
82
83 swapped = false;
84
85
86 //Debug.WriteLine(p);
87 //Debug.WriteLine("Testing " + current.ToString());
88
89 while (current.next != null)
90 {
91 // Because we need to call this method, the SortedList
92 // class is constrained on IEnumerable<T>
93 if (current.Data.CompareTo(current.next.Data) > 0)
94 {
95 Node tmp = current.next;
96 current.next = current.next.next;
97 tmp.next = current;
98
99 if (previous == null)
100 {
101 head = tmp;
102 }
103 else
104 {
105 previous.next = tmp;
106 }
107 previous = tmp;
108 swapped = true;
109 }
110 else
111 {
112 previous = current;
113 current = current.next;
114 }
115 }
116 } while (swapped);
117 }
118 }

A class type in C# can be initialized with null or a value which is of a compatible type with the declaration. Lines 76 and 77 look like so
Node previous = null;
Node current = head;
Here the value null is legal. It essentially says "I have no value". The assignment to head is also legal because head is also of type Node. The result is the two references head and current refer to the same Node object value. Modifying the Node instance through one of the references will be visible to the other.

You're assigning previous and next to null and head respectively. It's an assignment operation, just like any other. You don't need to use new unless you're actually creating a new instance of the object.
The generic parts are anything that refers to T. It's a generic type that is supplied when the class is instanciated. A good example is List<T>, which creates a list of objects of type T. You could instance this as List<string> for a list of strings, List<int> for a list of ints, etc.

These are references that could be pointing to instances of a class or can be just null.
You can assign references to other references:
Foo f1 = new Foo();
Foo f2 = f1;
Foo f3 = null;

No objects are being instantiated on lines 76 and 77 in that code. As you said, Node is a class. Classes in .NET are always reference types which means that:
The value of a variable of a reference type is a reference to an object (or nothing).
Variables of a reference type can be assigned the value null, which means that the variable references nothing.
Assigning one variable of a reference type to another variable of a reference type copies the reference, not the object.