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LPC4088DM Using Images

Table of Contents

  1. Image Formats
  2. Images on the File System
  3. Images in Flash
  4. Showing the Image
  5. Performance

The DMBasicGUI library comes with, among other things, a image decoding.

Images are decoded using the Image class:

Import library
DMBasicGUI - Image Class Reference

Static Public Member Functions

static int decode (const unsigned char *pDataIn, unsigned int sizeIn, Resolution res, ImageData_t *pDataOut)
Decodes the specified image data.
static int decode (const char *filename, Resolution res, ImageData_t *pDataOut, Mutex *pLock=NULL)
Reads the specified file and decodes the image data.

Image Formats

Currently three image formats are supported at runtime:

  • Portable Network Graphics (*.png)
  • Bitmaps (*.bmp)
  • Raw images (*.raw)

PNG and BMP are both standard formats, but the RAW image is a special format that is used in this library. The RAW images contain a 10-byte header (including the width and height of the image) and the uncompressed data.

it takes no time to decode a RAW image, but it will take up more space than e.g. a PNG image. The RAW image always uses (width*height*2 + 10) bytes to store the image, regardless of what is in the image.

To convert a image from any format into *.raw use the imgConverter.py script. As the conversion into the raw format is done on a PC the input format is limited only by the python image library which supports many more formats and not just PNG and BMP.

There is a section about image files on the Performance wiki page.

Images on the File System

If the image is stored on the file system:

#include "Image.h"
...
// decode an image from a file
Image::ImageData_t img;
if (Image::decode("/ram/image.png", &img) == 0) {
    // draw on display using img.pixels, img.width and img.height
    ...
    free(img.pointerToFree);
}


Images in Flash

Images can also be compiled into the program so that it doesn't require a uSD card or a USB Memory Stick. The img2c.py script can be used to prepare the images.

The output of the script looks something like this:

image_data.h

#include "basic_image_data.h"

extern const unsigned char img_empty[];
extern const unsigned int img_size_empty;


image_data.cpp

#define IMAGE_LOCATION
//#define IMAGE_LOCATION  __attribute__((section("SPIFI_MEM"))) 

const unsigned char img_empty[] = {
	0x89,0x50,0x4E,0x47,0x0D,0x0A,0x1A,0x0A,0x00,0x00,0x00,0x0D,0x49,0x48,0x44,0x52, 
	0x00,0x00,0x00,0x40,0x00,0x00,0x00,0x40,0x08,0x02,0x00,0x00,0x00,0x25,0x0B,0xE6, 
	0x89,0x00,0x00,0x00,0x09,0x70,0x48,0x59,0x73,0x00,0x00,0x0E,0xC4,0x00,0x00,0x0E, 
	0xC4,0x01,0x95,0x2B,0x0E,0x1B,0x00,0x00,0x02,0x8B,0x49,0x44,0x41,0x54,0x78,0x9C, 
        ...
	0x49,0x9C,0xF0,0xEB,0x0F,0xB7,0x97,0x16,0xD2,0x38,0x59,0xDC,0x57,0x00,0x00,0x00, 
	0x00,0x49,0x45,0x4E,0x44,0xAE,0x42,0x60,0x82
};
const unsigned int img_size_empty = sizeof(img_empty);


To load such an image in your program:

#include "Image.h"
#include "image_data.h"
...
// decode an image from a file
Image::ImageData_t img;
if (Image::decode(img_empty, img_size_empty, &img) == 0) {
    // draw on display using img.pixels, img.width and img.height
    ...
    free(img.pointerToFree);
}


Note

The IMAGE_LOCATION define can be used to move the image data into the external QSPI flash to save space in the internal flash for code.

Showing the Image

Displaying the decoded image can be as simple as drawing directly on the framebuffer (assuming the image is the same size as the display):

#include "mbed.h"
#include "DMBoard.h"
#include "Image.h"

void main() {
  // initialize DMBoard
  ...
  // create the frame buffer
  void* fb = disp->allocateFramebuffer();
  
  // decode the image
  Image::ImageData_t img;
  if (Image::decode("/ram/image.png", &img) == 0) {
    // draw on display using img.pixels, img.width and img.height
    memcpy(fb, img.pixels, img.width * img.height * 2);

    // now that the image has been copied, the raw data can be freed
    free(img.pointerToFree);

    // Start display in default mode (16-bit)
    Display::DisplayError disperr = disp->powerUp(fb);
    if (disperr != Display::DisplayError_Ok) {
      // Failed to initialize the display
    }
  }
 ...
}


The SWIM library contains functions to help when drawing images. There are functions to rotate, scale and invert images.

Performance

The performance of the MCI, USB Host MassStorage and QSPI file systems has been measured as well as the performance of decoding images stored on each of them. The result is available on thePerformance wiki page.

All wikipages