RAW12, RAW14, JPEG, TIFF影像格式

1. JPEG, TIFF:
   大小: 寬 * 高 * 1 byte (8 bits)
   顏色: 每個點擁有2的8次方 = 256 個層級，因此8bit的JPEG可以表示出256(R) * 256(G) * 256(B) = 16,777,216 = 16.77M 種顏色。

2. RAW 12:
   大小: 寬 * 高 * 1.5 byte (12 bits)
   顏色: 每個點擁有2的12次方 = 4096 個層級，因此RAW 12bit可表示出4096(R) * 4096(G) * 4096(B) = 68,719,476,736 = 68700M = 68.7G 種顏色。
3. RAW 14:
   大小: 寬 * 高 * 1.75 byte (14 bits)
   顏色: 每個點擁有2的14次方 = 16384 個級，因此14bit RAW可表示出16384(R) * 16384(G) * 16384(B) = 4,398,046,511,104 = 4398000M = 4398G = 4.398T 種顏色。

4. BMP 16
5. BMP 24
6. PPM (portable pixmap format)


7. 單眼中，每個檔案格式的大小
RAW 14-bit 未壓縮, 74.4MB, 103張
RAW 14-bit 無損壓縮, 41.3MB, 103張
RAW 14-bit 壓縮, 35.9MB, 151張
RAW 12-bit 未壓縮, 57.0MB, 133張
RAW 12-bit 無損壓縮, 32.4MB, 133張
RAW 12-bit 壓縮, 29.0MB, 182張

TIFF (RGB) -L 108.2MB, 71張
TIFF (RGB) -M 61.5MB, 126張
TIFF (RGB) -S 28.0MB, 277張

JPEG fine -L 16.3 MB, 360張
JPEG fine -M 10.4 MB, 616張
JPEG fine -S 5.2 MB, 1200張
JPEG normal -L 9.1 MB, 718張
JPEG normal -M 5.3 MB, 1200張
JPEG normal -S 2.6 MB, 2400張
JPEG basic -L 4.0 MB, 1400張
JPEG basic -M 2.7 MB, 2400張
JPEG basic -S 1.4 MB, 4800張

User space存取記憶體: devmem

1. 透過devmem，可以在userspace存取記憶體

2. 範例

/*
 * devmem2.c: Simple program to read/write from/to any location in memory.
 *
 *  Copyright (C) 2000, Jan-Derk Bakker (J.D.Bakker@its.tudelft.nl)
 *
 *
 * This software has been developed for the LART computing board
 * (http://www.lart.tudelft.nl/). The development has been sponsored by
 * the Mobile MultiMedia Communications (http://www.mmc.tudelft.nl/)
 * and Ubiquitous Communications (http://www.ubicom.tudelft.nl/)
 * projects.
 *
 * The author can be reached at:
 *
 *  Jan-Derk Bakker
 *  Information and Communication Theory Group
 *  Faculty of Information Technology and Systems
 *  Delft University of Technology
 *  P.O. Box 5031
 *  2600 GA Delft
 *  The Netherlands
 *
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
  
#define FATAL do { fprintf(stderr, "Error at line %d, file %s (%d) [%s]\n", \
  __LINE__, __FILE__, errno, strerror(errno)); exit(1); } while(0)
 
#define MAP_SIZE 4096UL
#define MAP_MASK (MAP_SIZE - 1)

int main(int argc, char **argv) {
    int fd;
    void *map_base, *virt_addr; 
 unsigned long read_result, writeval;
 off_t target;
 int access_type = 'w';
 
 if(argc < 2) {
  fprintf(stderr, "\nUsage:\t%s { address } [ type [ data ] ]\n"
   "\taddress : memory address to act upon\n"
   "\ttype    : access operation type : [b]yte, [h]alfword, [w]ord\n"
   "\tdata    : data to be written\n\n",
   argv[0]);
  exit(1);
 }
 target = strtoul(argv[1], 0, 0);

 if(argc > 2)
  access_type = tolower(argv[2][0]);


    if((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) FATAL;
    printf("/dev/mem opened.\n"); 
    fflush(stdout);
    
    /* Map one page */
    map_base = mmap(0, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, target & ~MAP_MASK);
    if(map_base == (void *) -1) FATAL;
    printf("Memory mapped at address %p.\n", map_base); 
    fflush(stdout);
    
    virt_addr = map_base + (target & MAP_MASK);
    switch(access_type) {
  case 'b':
   read_result = *((unsigned char *) virt_addr);
   break;
  case 'h':
   read_result = *((unsigned short *) virt_addr);
   break;
  case 'w':
   read_result = *((unsigned long *) virt_addr);
   break;
  default:
   fprintf(stderr, "Illegal data type '%c'.\n", access_type);
   exit(2);
 }
    printf("Value at address 0x%X (%p): 0x%X\n", target, virt_addr, read_result); 
    fflush(stdout);

 if(argc > 3) {
  writeval = strtoul(argv[3], 0, 0);
  switch(access_type) {
   case 'b':
    *((unsigned char *) virt_addr) = writeval;
    read_result = *((unsigned char *) virt_addr);
    break;
   case 'h':
    *((unsigned short *) virt_addr) = writeval;
    read_result = *((unsigned short *) virt_addr);
    break;
   case 'w':
    *((unsigned long *) virt_addr) = writeval;
    read_result = *((unsigned long *) virt_addr);
    break;
  }
  printf("Written 0x%X; readback 0x%X\n", writeval, read_result); 
  fflush(stdout);
 }
 
 if(munmap(map_base, MAP_SIZE) == -1) FATAL;
    close(fd);
    return 0;
}

3. 使用方法

$ ./devmem

Usage:  ./devmem { address } [ type [ data ] ]
        address : memory address to act upon
        type    : access operation type : [b]yte, [h]alfword, [w]ord
        data    : data to be written

讀取記憶體

$ devmem 0x97000000 32

寫入記憶體

$ devmem 0x97000000 32 0x00000000

4. 參考來源 http://free-electrons.com/pub/mirror/devmem2.c