TFT 1.54" Teensy 3.6 Bitmap from SD card wrong colour

I am trying to get the Adafruit 1.54" 240x240 Wide Angle TFT ST7789 working with a Teensy 3.6, using the Adafruit library, by reading the bitmaps from the SD card but colours on the screen do not match the bitmap (See attached file). I think the problem was in the display library Color definitions section, but this does not affect the bitamp. I have drawn blocks of colour, but there are very different to the display.

Is the problem with the code or how the bitmap images are generated and saved?

#include <Adafruit_GFX.h>    // Core graphics library
#include <ST7735_t3.h> // Hardware-specific library
#include <ST7789_t3.h> // Hardware-specific library
#include <SPI.h>
#include <SD.h>
#include <Arduino_ST7789.h> // Hardware-specific library for ST7789 (with or without CS pin)

#define BUFFPIXEL 20

File myFile;
char picturefilename[300];
char picturefiledelay[300];

File root;

const int chipSelect = BUILTIN_SDCARD;

#define filenameflag = 1;
#define timedelaynameflag = 2;

#define TFT_SCLK 13  // SCLK can also use pin 14
#define TFT_MOSI 11  // MOSI can also use pin 7
#define TFT_CS   10  // CS & DC can use pins 2, 6, 9, 10, 15, 20, 21, 22, 23
#define TFT_DC    9  //  but certain pairs must NOT be used: 2+10, 6+9, 20+23, 21+22
#define TFT_RST   8  // RST can use any pin
#define SD_CS     BUILTIN_SDCARD  // CS for SD card, can use any pin

// Option 1: use any pins but a little slower
// Note: code will detect if specified pins are the hardware SPI pins
//       and will use hardware SPI if appropriate
// For 1.44" and 1.8" TFT with ST7735 use
//ST7735_t3 tft = ST7735_t3(TFT_CS, TFT_DC, TFT_MOSI, TFT_SCLK, TFT_RST);

// For 1.54" or other TFT with ST7789, This has worked with some ST7789
// displays without CS pins, for those you can pass in -1 or 0xff for CS
// More notes by the tft.init call
//ST7789_t3 tft = ST7789_t3(TFT_CS, TFT_DC, TFT_MOSI, TFT_SCLK, TFT_RST);
Arduino_ST7789 tft = Arduino_ST7789(-1, TFT_RST, TFT_MOSI, TFT_SCLK, TFT_CS); //for display with CS pin and DC via 9bit SPI



float p = 3.1415926;


void setup(void) 
{
  pinMode(SD_CS, INPUT_PULLUP);  // don't touch the SD card

  Serial.begin(9600);
  Serial.print("hello!");

  // Or use this initializer (uncomment) if you're using a 1.54" 240x240 TFT
  tft.init(240, 240);   // initialize a ST7789 chip, 240x240 pixels
  tft.fillScreen(BLACK); red
  delay(5000);
  tft.fillScreen(BLUE);
  delay(5000);
  tft.fillScreen(YELLOW); 
  delay(5000);
  
   Serial.println("Initializing SD card...");
  if (!SD.begin(SD_CS)) {
    Serial.println("failed!");
    tft.fillScreen(ST7735_BLACK);
    tft.setCursor(5, tft.height()/2 - 6);
    tft.print("Unable to access");
    tft.setCursor(32, tft.height()/2 + 6);
    tft.print("SD card");
    
    while (1) {
      writedrawtext("Error with SD Card", ST7735_WHITE, 0 ,0);
    }
  }
  Serial.println("Screen and SD card has all started");

}



void loop()
{
  int i, ptr2, timedelay;
  String tmp;


bmpDraw("320x320.bmp",0,0);
delay(1000);
    
}




#define BUFFPIXEL 20

void bmpDraw(const char *filename, uint8_t x, uint8_t y) {

  File     bmpFile;
  int      bmpWidth, bmpHeight;   // W+H in pixels
  uint8_t  bmpDepth;              // Bit depth (currently must be 24)
  uint32_t bmpImageoffset;        // Start of image data in file
  uint32_t rowSize;               // Not always = bmpWidth; may have padding
  uint8_t  sdbuffer[3*BUFFPIXEL]; // pixel buffer (R+G+B per pixel)
  uint8_t  buffidx = sizeof(sdbuffer); // Current position in sdbuffer
  boolean  goodBmp = false;       // Set to true on valid header parse
  boolean  flip    = true;        // BMP is stored bottom-to-top
  int      w, h, row, col;
  uint8_t  r, g, b;
  uint32_t pos = 0, startTime = millis();

  if((x >= tft.width()) || (y >= tft.height())) return;

  Serial.println();
  Serial.print("Loading image '");
  Serial.print(filename);
  Serial.println('\'');

  // Open requested file on SD card
  bmpFile = SD.open(filename);
  if (!bmpFile) {
    Serial.print("File not found");
    tft.fillScreen(ST7735_BLACK);
    tft.setCursor(12, tft.height()/2 - 12);
    tft.print("Unable to");
    tft.setCursor(12, tft.height()/2 - 0);
    tft.print("read file: ");
    tft.setCursor(12, tft.height()/2 + 12);
    tft.setTextColor(ST7735_YELLOW);
    tft.print(filename);
    return;
  }

  // Parse BMP header
  if(read16(bmpFile) == 0x4D42) { // BMP signature
    Serial.print("File size: "); Serial.println(read32(bmpFile));
    (void)read32(bmpFile); // Read & ignore creator bytes
    bmpImageoffset = read32(bmpFile); // Start of image data
    Serial.print("Image Offset: "); Serial.println(bmpImageoffset, DEC);
    // Read DIB header
    Serial.print("Header size: "); Serial.println(read32(bmpFile));
    bmpWidth  = read32(bmpFile);
    bmpHeight = read32(bmpFile);
    if(read16(bmpFile) == 1) { // # planes -- must be '1'
      bmpDepth = read16(bmpFile); // bits per pixel
      Serial.print("Bit Depth: "); Serial.println(bmpDepth);
      if((bmpDepth == 24) && (read32(bmpFile) == 0)) { // 0 = uncompressed

        goodBmp = true; // Supported BMP format -- proceed!
        Serial.print("Image size: ");
        Serial.print(bmpWidth);
        Serial.print('x');
        Serial.println(bmpHeight);

        // BMP rows are padded (if needed) to 4-byte boundary
        rowSize = (bmpWidth * 3 + 3) & ~3;

        // If bmpHeight is negative, image is in top-down order.
        // This is not canon but has been observed in the wild.
        if(bmpHeight < 0) {
          bmpHeight = -bmpHeight;
          flip      = false;
        }

        // Crop area to be loaded
        w = bmpWidth;
        h = bmpHeight;
        if((x+w-1) >= tft.width())  w = tft.width()  - x;
        if((y+h-1) >= tft.height()) h = tft.height() - y;

        // Set TFT address window to clipped image bounds
        tft.setAddrWindow(x, y, x+w-1, y+h-1);

        for (row=0; row<h; row++) { // For each scanline...

          // Seek to start of scan line.  It might seem labor-
          // intensive to be doing this on every line, but this
          // method covers a lot of gritty details like cropping
          // and scanline padding.  Also, the seek only takes
          // place if the file position actually needs to change
          // (avoids a lot of cluster math in SD library).
          if(flip) // Bitmap is stored bottom-to-top order (normal BMP)
            pos = bmpImageoffset + (bmpHeight - 1 - row) * rowSize;
          else     // Bitmap is stored top-to-bottom
            pos = bmpImageoffset + row * rowSize;
          if(bmpFile.position() != pos) { // Need seek?
            bmpFile.seek(pos);
            buffidx = sizeof(sdbuffer); // Force buffer reload
          }

          for (col=0; col<w; col++) { // For each pixel...
            // Time to read more pixel data?
            if (buffidx >= sizeof(sdbuffer)) { // Indeed
              bmpFile.read(sdbuffer, sizeof(sdbuffer));
              buffidx = 0; // Set index to beginning
            }

            // Convert pixel from BMP to TFT format, push to display
            b = sdbuffer[buffidx++];
            g = sdbuffer[buffidx++];
            r = sdbuffer[buffidx++];
           // tft.pushColor(tft.Color565(r,g,b));
            tft.pushColor(tft.Color565(r,g,b));
            
          } // end pixel
        } // end scanline
        Serial.print("Loaded in ");
        Serial.print(millis() - startTime);
        Serial.println(" ms");
      } // end goodBmp
    }
  }

  bmpFile.close();
  if(!goodBmp)
  {
         tft.fillScreen(ST7735_BLACK);
         writedrawtext("Error with picture format", ST7735_WHITE, 0, 0); 
         writedrawtext(filename, ST7735_WHITE, 0, 40); 
  }


  
}

// These read 16- and 32-bit types from the SD card file.
// BMP data is stored little-endian, Arduino is little-endian too.
// May need to reverse subscript order if porting elsewhere.

uint16_t read16(File f) {
  uint16_t result;
  ((uint8_t *)&result)[0] = f.read(); // LSB
  ((uint8_t *)&result)[1] = f.read(); // MSB
  return result;
}

uint32_t read32(File f) {
  uint32_t result;
  ((uint8_t *)&result)[0] = f.read(); // LSB
  ((uint8_t *)&result)[1] = f.read();
  ((uint8_t *)&result)[2] = f.read();
  ((uint8_t *)&result)[3] = f.read(); // MSB
  return result;
}

void writedrawtext(const char *text, uint16_t color, int x, int y) {
  tft.setCursor(x, y);
  tft.setTextColor(color);
  tft.setTextWrap(true);
  tft.print(text);
}
// Color definitions
#define	BLACK   0x0000
#define	BLUE    0x001F
#define	RED     0xF800
#define	GREEN   0x07E0
#define CYAN    0x07FF
#define MAGENTA 0xF81F
#define YELLOW  0xFFE0
#define WHITE   0xFFFF

screencolours.png

Well looking at your image it looks like two color channels could be swapped.

// Convert pixel from BMP to TFT format, push to display b = sdbuffer[buffidx++]; g = sdbuffer[buffidx++]; r = sdbuffer[buffidx++]; // tft.pushColor(tft.Color565(r,g,b)); tft.pushColor(tft.Color565(r,g,b));

Black is converted correctly because its all 0. Green seems to be green on the left and the right side of the picture. Yellow is a combination of two color so is cyan. Blue is just one color and it appears red which is only one color. Additionaly its called RGB likely the bytes are stored in that order in your BMP. You read blue green red. Try changing it to

r = sdbuffer[buffidx++]; g = sdbuffer[buffidx++]; b = sdbuffer[buffidx++];

You have clearly got Blue and Green swapped.
What did you see at startup? BLACK → BLUE → YELLOW ?

I ran your program on a Uno with Adafruit_ST7789 and Arduino_ST7789 libraries.
I used HW SPI with separate DC line. And changed the ST7735_COLOR to a standard TFT_XXXX
Other changes are commented “.kbv”

I don’t see that SD would be possible on the SPI bus if you are bit-banging SW SPI for the TFT.
Does your Teensy use two SPI buses?

Does your display use 9-bit SPI ?

I have attached my working sketch. My colours are good with both libraries.

Is your “320x320.bmp” good?
Perhaps it is in an unexpected format. Attach the .BMP file you are using. (you will need to put it inside a ZIP file because the Forum does not accept .BMP)

David.

brendonshaw_BMP.ino (9.52 KB)