如何在 ObjectiveC/C++ 中打開 LinearDNG？

Question

我試圖在我的 MacOS 應用程序中打開LinearDNG文件。 據我調查，這是不可能的CoreImage 。

所以，問題：

1. 是否可以使用CoreImage將LinearDNG文件打開為 16 位/8 位 RGBA 數據？
2. 是否可以使用dcraw將LinearDNG文件作為 16 位/8 位 RGBA 數據打開？
3. 您知道將LinearDNG文件作為 16 位/8 位 RGBA 數據打開的其他庫嗎？

我的 LinearDNG 文件是 16 位的。 相關EXIF數據：

File Type                       : DNG
File Type Extension             : dng
MIME Type                       : image/x-adobe-dng

Bits Per Sample                 : 16 16 16
Compression                     : Uncompressed
Photometric Interpretation      : Linear Raw

Format                          : image/jpeg

我讀過CIContext可以將圖像轉換為TIFF/JPEG ，但是帶有這個特定LinearDNG文件的代碼不起作用。 所有 JPEG 圖像都是黑色的，所有 TIFF 圖像都是透明的。 我猜CIImage只是不理解這種編碼。

我的測試代碼：

[self convertLinearDNGToJPEG:@"super_jpeg.jpeg"];
        
[self convertLinearDNGToTIFF:kCIFormatRGBA8 fileName:@"super_kCIFormatRGBA8.tiff"];
[self convertLinearDNGToTIFF:kCIFormatRGBA16 fileName:@"super_kCIFormatRGBA16.tiff"];
[self convertLinearDNGToTIFF:kCIFormatARGB8 fileName:@"super_kCIFormatARGB8.tiff"];
[self convertLinearDNGToTIFF:kCIFormatRGBAh fileName:@"super_kCIFormatRGBAh.tiff"];

相應的函數（ convertLinearDNGToTIFF / convertLinearDNGToJPEG ）：

- (void)convertLinearDNGToJPEG:(NSString*)fileName
{
    CIImage* inputImage = [self createInputImage];
    
    NSError* superError = nil;
    CIContext* ciContext = [self createCiContext];
    
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    
    NSURL* superURL = [NSURL fileURLWithPath: [documentsDirectory stringByAppendingPathComponent:fileName] ];
    CGColorSpaceRef superColorSpace = CGColorSpaceCreateDeviceRGB();
    [ciContext writeJPEGRepresentationOfImage:inputImage
                                        toURL:superURL
                                   colorSpace:superColorSpace
                                      options:@{} // CIImageRepresentationOption
                                        error:&superError];
}
- (void)convertLinearDNGToTIFF:(CIFormat)format fileName:(NSString*)fileName
{
    CIImage* inputImage = [self createInputImage];
    
    NSError* superError = nil;
    CIContext* ciContext = [self createCiContext];
    
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    
    NSURL* superURL = [NSURL fileURLWithPath: [documentsDirectory stringByAppendingPathComponent:fileName] ];
    CGColorSpaceRef superColorSpace = CGColorSpaceCreateDeviceRGB();
    [ciContext writeTIFFRepresentationOfImage:inputImage
                                        toURL:superURL
                                       format:format
                                   colorSpace:superColorSpace
                                      options:@{} // CIImageRepresentationOption
                                        error:&superError];
}

Answer 1

好吧，我試過 LibRaw： https://github.com/LibRaw/LibRaw 。 它能夠將我的LinearDNG導出到 TIFF。 我可以用CoreImage打開 TIFF。 但是白平衡是錯誤的。 我認為這是因為libraw讀取元數據錯誤（文件samples/raw-identify.cpp ）。

導出到 TIFF 的代碼在文件samples/simple_dcraw.cpp

/* -*- C++ -*-
 * File: simple_dcraw.cpp
 * Copyright 2008-2020 LibRaw LLC (info@libraw.org)
 * Created: Sat Mar  8, 2008
 *
 * LibRaw simple C++ API:  emulates call to "dcraw  [-D]  [-T] [-v] [-e] [-4]"

LibRaw is free software; you can redistribute it and/or modify
it under the terms of the one of two licenses as you choose:

1. GNU LESSER GENERAL PUBLIC LICENSE version 2.1
   (See file LICENSE.LGPL provided in LibRaw distribution archive for details).

2. COMMON DEVELOPMENT AND DISTRIBUTION LICENSE (CDDL) Version 1.0
   (See file LICENSE.CDDL provided in LibRaw distribution archive for details).


 */
#include <stdio.h>
#include <string.h>
#include <math.h>

#include "libraw/libraw.h"

#ifndef LIBRAW_WIN32_CALLS
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/mman.h>
#endif

#ifdef LIBRAW_WIN32_CALLS
#define snprintf _snprintf
#endif

int my_progress_callback(void *unused_data, enum LibRaw_progress state,
                         int iter, int expected)
{
  if (iter == 0)
    printf("CB: state=%x, expected %d iterations\n", state, expected);
  return 0;
}

char *customCameras[] = {
    (char *)"43704960,4080,5356, 0, 0, 0, 0,0,148,0,0, Dalsa, FTF4052C Full,0",
    (char *)"42837504,4008,5344, 0, 0, 0, 0,0,148,0,0,Dalsa, FTF4052C 3:4",
    (char *)"32128128,4008,4008, 0, 0, 0, 0,0,148,0,0,Dalsa, FTF4052C 1:1",
    (char *)"24096096,4008,3006, 0, 0, 0, 0,0,148,0,0,Dalsa, FTF4052C 4:3",
    (char *)"18068064,4008,2254, 0, 0, 0, 0,0,148,0,0,Dalsa, FTF4052C 16:9",
    (char *)"67686894,5049,6703, 0, 0, 0, 0,0,148,0,0,Dalsa, FTF5066C Full",
    (char *)"66573312,4992,6668, 0, 0, 0, 0,0,148,0,0,Dalsa, FTF5066C 3:4",
    (char *)"49840128,4992,4992, 0, 0, 0, 0,0,148,0,0,Dalsa, FTF5066C 1:1",
    (char *)"37400064,4992,3746, 0, 0, 0, 0,0,148,0,0,Dalsa, FTF5066C 4:3",
    (char *)"28035072,4992,2808, 0, 0, 0, 0,0,148,0,0,Dalsa, FTF5066C 16:9",
    NULL};

int main(int ac, char *av[])
{
  int i, ret, verbose = 0, output_thumbs = 0;

  // don't use fixed size buffers in real apps!
  char outfn[1024], thumbfn[1024];

  LibRaw* RawProcessor = new LibRaw;
  RawProcessor->imgdata.params.custom_camera_strings = customCameras;
  if (ac < 2)
  {
    printf("simple_dcraw - LibRaw %s sample. Emulates dcraw [-D] [-T] [-v] "
           "[-e] [-E]\n"
           " %d cameras supported\n"
           "Usage: %s [-D] [-T] [-v] [-e] raw-files....\n"
           "\t-4 - 16-bit mode\n"
           "\t-L - list supported cameras and exit\n"
           "\t-v - verbose output\n"
           "\t-T - output TIFF files instead of .pgm/ppm\n"
           "\t-e - extract thumbnails (same as dcraw -e in separate run)\n",
           LibRaw::version(), LibRaw::cameraCount(), av[0]);
    delete RawProcessor;
    return 0;
  }

  putenv((char *)"TZ=UTC"); // dcraw compatibility, affects TIFF datestamp field

#define P1 RawProcessor->imgdata.idata
#define S RawProcessor->imgdata.sizes
#define C RawProcessor->imgdata.color
#define T RawProcessor->imgdata.thumbnail
#define P2 RawProcessor->imgdata.other
#define OUT RawProcessor->imgdata.params

  for (i = 1; i < ac; i++)
  {
    if (av[i][0] == '-')
    {
      if (av[i][1] == 'T' && av[i][2] == 0)
        OUT.output_tiff = 1;
      if (av[i][1] == 'v' && av[i][2] == 0)
        verbose++;
      if (av[i][1] == 'e' && av[i][2] == 0)
        output_thumbs++;
      if (av[i][1] == '4' && av[i][2] == 0)
        OUT.output_bps = 16;
      if (av[i][1] == 'C' && av[i][2] == 0)
        RawProcessor->set_progress_handler(my_progress_callback, NULL);
      if (av[i][1] == 'L' && av[i][2] == 0)
      {
        const char **clist = LibRaw::cameraList();
        const char **cc = clist;
        while (*cc)
        {
          printf("%s\n", *cc);
          cc++;
        }
        delete RawProcessor;
        exit(0);
      }
      continue;
    }

    if (verbose)
      printf("Processing file %s\n", av[i]);

    if ((ret = RawProcessor->open_file(av[i])) != LIBRAW_SUCCESS)
    {
      fprintf(stderr, "Cannot open_file %s: %s\n", av[i], libraw_strerror(ret));
      continue; // no recycle b/c open file will recycle itself
    }

    if (!output_thumbs) // No unpack for thumb extraction
      if ((ret = RawProcessor->unpack()) != LIBRAW_SUCCESS)
      {
        fprintf(stderr, "Cannot unpack %s: %s\n", av[i], libraw_strerror(ret));
        continue;
      }

    // thumbnail unpacking and output in the middle of main
    // image processing - for test purposes!
    if (output_thumbs)
    {
      if ((ret = RawProcessor->unpack_thumb()) != LIBRAW_SUCCESS)
      {
        fprintf(stderr, "Cannot unpack_thumb %s: %s\n", av[i],
                libraw_strerror(ret));
        if (LIBRAW_FATAL_ERROR(ret))
          continue; // skip to next file
      }
      else
      {
        snprintf(thumbfn, sizeof(thumbfn), "%s.%s", av[i],
                 T.tformat == LIBRAW_THUMBNAIL_JPEG ? "thumb.jpg"
                                                    : "thumb.ppm");

        if (verbose)
          printf("Writing thumbnail file %s\n", thumbfn);
        if (LIBRAW_SUCCESS != (ret = RawProcessor->dcraw_thumb_writer(thumbfn)))
        {
          fprintf(stderr, "Cannot write %s: %s\n", thumbfn,
                  libraw_strerror(ret));
          if (LIBRAW_FATAL_ERROR(ret))
            continue;
        }
      }
      continue;
    }

    ret = RawProcessor->dcraw_process();

    if (LIBRAW_SUCCESS != ret)
    {
      fprintf(stderr, "Cannot do postpocessing on %s: %s\n", av[i],
              libraw_strerror(ret));
      if (LIBRAW_FATAL_ERROR(ret))
        continue;
    }
    snprintf(outfn, sizeof(outfn), "%s.%s", av[i],
             OUT.output_tiff ? "tiff" : (P1.colors > 1 ? "ppm" : "pgm"));

    if (verbose)
      printf("Writing file %s\n", outfn);

    if (LIBRAW_SUCCESS != (ret = RawProcessor->dcraw_ppm_tiff_writer(outfn)))
      fprintf(stderr, "Cannot write %s: %s\n", outfn, libraw_strerror(ret));

    RawProcessor->recycle(); // just for show this call
  }
  
  delete RawProcessor;
  return 0;
}