feat(imageInput): Implement Image parsing from mnist_test.info

Startcode/imageInput.c

@@ -6,17 +6,145 @@
 #define BUFFER_SIZE 100
 #define FILE_HEADER_STRING "__info2_image_file_format__"
 
-// TODO Implementieren Sie geeignete Hilfsfunktionen für das Lesen der Bildserie aus einer Datei
 
-// TODO Vervollständigen Sie die Funktion readImages unter Benutzung Ihrer Hilfsfunktionen
+/*
+ * Aufbau der mnist_test.info2
+ *
+ *  Offset  Inhalt                        Typ
+ *  ------  ----------------------------  ----------------------------------
+ *  0       "__info2_image_file_format__" 26 ASCII-Zeichen
+ *  26      Anzahl der Bilder             unsigned short (2 Bytes)      10 27 -> 27 10 -> 10000
+ *  28      Breite eines Bildes           unsigned short (2 Bytes)      1C 00 -> 00 1C -> 28
+ *  30      Höhe eines Bildes             unsigned short (2 Bytes)      1C 00 -> 00 1C -> 28
+ *  32      Bild 0:  width*height Pixel   unsigned char je Pixel (Graustufe 0-255)
+ *          direkt danach: Label 0        unsigned char (Klasse 0-9)
+ * 
+ *  usw...
+ */
+
+
+//prüft, ob die Datei mit dem erwarteten Dateitag beginnt
+static int checkFileTag(FILE *file)
+{
+    int isValid = 0;
+    size_t tagLength = strlen(FILE_HEADER_STRING);
+    char buffer[BUFFER_SIZE] = {0};
+
+    if(tagLength < BUFFER_SIZE && fread(buffer, sizeof(char), tagLength, file) == tagLength)
+    {
+        isValid = strncmp(buffer, FILE_HEADER_STRING, tagLength) == 0;
+    }
+
+    return isValid;
+}
+
+//liest Anzahl, Breite und Höhe der Bildserie; Erfolg nur, wenn alle Werte gelesen werden konnten und positiv sind
+static int readSeriesHeader(FILE *file, unsigned short *count, unsigned short *width, unsigned short *height)
+{
+    return fread(count, sizeof(unsigned short), 1, file) == 1
+        && fread(width, sizeof(unsigned short), 1, file) == 1
+        && fread(height, sizeof(unsigned short), 1, file) == 1
+        && *count > 0 && *width > 0 && *height > 0;
+}
+
+//liest die Pixelwerte eines einzelnen Bildes; buffer ist NULL im Fehlerfall
+static GrayScaleImage readImage(FILE *file, unsigned int width, unsigned int height)
+{
+    GrayScaleImage image = {NULL, 0, 0};
+
+    GrayScalePixelType *buffer = (GrayScalePixelType *)calloc(width * height, sizeof(GrayScalePixelType));
+
+    if(buffer != NULL && fread(buffer, sizeof(GrayScalePixelType), width * height, file) == width * height)
+    {
+        image.buffer = buffer;
+        image.width = width;
+        image.height = height;
+    }
+    else
+    {
+        free(buffer);
+    }
+
+    return image;
+}
+
+//liest die Klasse (Label) des zuletzt gelesenen Bildes
+static int readLabel(FILE *file, unsigned char *label)
+{
+    return fread(label, sizeof(unsigned char), 1, file) == 1;
+}
+
+static int isValidSeries(const GrayScaleImageSeries *series)
+{
+    return series->images != NULL && series->labels != NULL && series->count > 0;
+}
+
 GrayScaleImageSeries *readImages(const char *path)
 {
     GrayScaleImageSeries *series = NULL;
+    FILE *file = fopen(path, "rb"); //Binärdatei, daher "rb"
+
+    if(file != NULL)
+    {
+        unsigned short count = 0;
+        unsigned short width = 0;
+        unsigned short height = 0;
+
+        if(checkFileTag(file) && readSeriesHeader(file, &count, &width, &height))
+        {
+            series = (GrayScaleImageSeries *)malloc(sizeof(GrayScaleImageSeries));              //struct containing *images, *lables and count
+
+            if(series != NULL)
+            {
+                series->images = (GrayScaleImage *)calloc(count, sizeof(GrayScaleImage));       //10000 * 784bytes in our example
+                series->labels = (unsigned char *)calloc(count, sizeof(unsigned char));         //10000bytes 1 for every picture in our example
+                series->count = count;
+
+                if(isValidSeries(series))
+                {
+                    int allRead = 1;
+
+                    for(unsigned int i = 0; i < count && allRead; i++)
+                    {
+                        series->images[i] = readImage(file, width, height);
+                        allRead = series->images[i].buffer != NULL && readLabel(file, &series->labels[i]);
+                    }
+
+                    if(!allRead)
+                    {
+                        clearSeries(series);
+                        series = NULL;
+                    }
+                }
+                else
+                {
+                    clearSeries(series);
+                    series = NULL;
+                }
+            }
+        }
+
+        fclose(file);
+    }
 
     return series;
 }
 
-// TODO Vervollständigen Sie die Funktion clearSeries, welche eine Bildserie vollständig aus dem Speicher freigibt
 void clearSeries(GrayScaleImageSeries *series)
 {
+    if(series != NULL)
+    {
+        if(series->images != NULL)
+        {
+            //erst die Pixelbuffer der einzelnen Bilder, dann das Array selbst
+            for(unsigned int i = 0; i < series->count; i++)
+            {
+                free(series->images[i].buffer);
+            }
+            free(series->images);
+        }
+
+        free(series->labels);
+        free(series);
+    }
 }