Complete newbie here.
I am following this thread: How to read bitmap image on Arduino specifically the third reply from : frarugi87 in my attempt to plot a monochromatic bitmap image with a plotter device. basically: bitmap>SD card board>arduino uno> plotted image
I attempted to modify their code to work with monocromatic bitmaps and removed the print to file function:
// MODIFIED CODE FROM BELOW CONTRIBUTOR
// (c) Michael Schoeffler 2016, http://www.mschoeffler.de
#include <SD.h> //Load SD library
int chipSelect = 4; //chip select pin for the MicroSD Card Adapter
File file; // file object that is used to read and write data
int32_t readNbytesInt(File *p_file, int position, byte nBytes) // FUNCTION WHICH READS A DETERMINED AMMOUNT OF BYTES INTO A SINGLE VARIABLE
{
if (nBytes > 4)
return 0;
p_file->seek(position);
int32_t weight = 1;
int32_t result = 0;
for (; nBytes; nBytes--)
{
result += weight * p_file->read();
weight <<= 8;
}
return result;
}
void setup() {
Serial.begin(9600); // start serial connection to print out debug messages and data
pinMode(chipSelect, OUTPUT); // chip select pin must be set to OUTPUT mode
if (!SD.begin(chipSelect)) { // Initialize SD card
Serial.println("Could not initialize SD card."); // if return value is false, something went wrong.
}
if (SD.exists("bitmap.bmp")) { // if "bitmap.bmp" exists, say so
Serial.println("Found The Bitmap File.");
}
file = SD.open("bitmap.bmp", FILE_READ); // open the file to an object for reading
// DETERMINE HOW LARGE THE BITMAP FILE IS
int howmany;
howmany = file.available();
Serial.println(howmany); // print the how large the file is
// DETERMINE STARTING IMAGE ARRAY LOCATION IN THE BITMAP FILE
int32_t dataStartingOffset = readNbytesInt(&file, 0x0A, 4);
Serial.println("The starting location in the fiile is...");
Serial.println(dataStartingOffset);
// DETERMINE THE IMAGE HEIGHT AND WIDTH
int32_t imgwidth = readNbytesInt(&file, 0x12, 4);
Serial.println("The image width is the following pixels:");
Serial.println(imgwidth);
int32_t imgheight = readNbytesInt(&file, 0x16, 4);
Serial.println(imgheight);
// MODIFIED CODE. DOES THE COLOR DEPTH LOCATION WORK IN THE BITMAP AND DOES IT GIVE CORRECT INFO ABOUT THE FILE?
int16_t pixelsize = readNbytesInt(&file, 0X1C, 2);
if (pixelsize != 24)
{
Serial.println("This image is most definitely not 24 bpp");
Serial.println(" it is actually a depth of :");
Serial.println(pixelsize);
}
file.seek(dataStartingOffset); //skip bitmap header and go directly to the image data array.
/* for(int32_t i = 0; i < imgheight; i ++) {
for (int32_t j = 0; j < imgwidth; j ++) {
B = file.read();
Serial.println("height and width location from bottom");
Serial.println(i);
Serial.println(j);
Serial.println("B");
Serial.println(B);
}
Serial.println("height advance");
}
*/
int B;
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
B = file.read();
Serial.println(B, BIN);
file.close();
Serial.println("done write");
}
But when I read a 16x16 monochromatic bitmap: see below
at what I assume is the color table starting location (given by dataStartingOffset variable) I get strings two bytes of correct color information, followed by two bytes of just...zeros. Is this a bitmap formatting thing?
serial output for 16x16 bitmap looks like this:(only up to 9 of the 16 lines starting from the bottom)
Found The Bitmap File. 126 The starting location in the file is... 62 The image width is the following pixels: 16 16 This image is most definitely not 24 bpp it is actually a depth of : 1 1111111 11111110 0 0 11111111 11111111 0 0 11111111 11111111 0 0 11111111 11111111 0 0 11111111 11111111 0 0 11111111 11111111 0 0 11111111 11111111 0 0 11111111 11111111 0 0 1111111 11111110 0 0 done write
and when I try to read a bitmap that is around 200 x 200 pixels, I get very strange height and width numbers that are negative and my above code does not work at all! Does a 16x16 bitmap have different byte structure formatting than a 200x200?
any help is appreciated. again I am a complete newbie here. I am just trying to figure out how to read a bitmap.