Extract Preview & Thumbnail from Nilon RAW Nef file

[MaximeOh]

I try to extract thumb & preview image from a Nikon RAW file.
For my test i use a lot of file from this bank.

I analyze all the exif tag with exiftool and i found some important things, there is 3 jpg images inside.

ExifIFDO

The image in IFD0 (determined by Strip Offsets & Strip byte counts) is not a jpg file and seems empty (a lot of zero inside).

ExifSubIFD

Exif tool tell me there is a small JPEG inside.

--- Exif Tool out ---
Jpg From Raw Start              : 1050112
Jpg From Raw Length             : 1216696
Jpg From Raw                    : (Binary data 1216696 bytes, use -b option to extract)

When i compare with extracted data via metadata-extractor, i have two tags in this directory, with the same values, but this tag is unknown by metadata-extractor.

----Metadata out - Exif SubIFD-----
Unknown tag (0x0201) : 1050112
Unknown tag (0x0202) : 1216696

But the code 0x0201 & 0x0202 are used in other Directory by metadata-extractor, in the ExifThumbnailDirectory class

  /**
     * The offset to thumbnail image bytes, relative to the start of the IFD.
     *
     * To obtain the offset relative to the start of the TIFF data stream, use
     * <code>getAdjustedThumbnailOffset</code>, which includes the value of
     * <code>getExifStartOffset</code>.
     */
    public static final int TAG_THUMBNAIL_OFFSET = 0x0201;
    /**
     * The size of the thumbnail image data in bytes.
     */
    public static final int TAG_THUMBNAIL_LENGTH = 0x0202;

So i can retrieve this values in my ExifSubIFDDirectory with ExifThumbnail constants :

ExifSubIFDDirectory exifSubDir =  ...
int offset = exifSubDir.getInt(ExifThumbnailDirectory.TAG_STRIP_OFFSETS);
int length = exifSubDir.getInt(ExifThumbnailDirectory.TAG_STRIP_BYTE_COUNTS);

Exif SubIFD Again

Yes, there are another dictionary with the same unknown tags (0x0201 & 0x0202).
I can extract it, cool.

-----Metadata out - Exif SubIFD----
New Subfile Type : Reduced-resolution image
Compression : JPEG (old-style)
X Resolution : 300 dots per inch
Y Resolution : 300 dots per inch
Resolution Unit : Inch
Unknown tag (0x0201) : 235520
Unknown tag (0x0202) : 814184
YCbCr Positioning : Datum point

Exif SubIFD Not a Jpg

i found another image, but it's not a jpg, maybe a tiff.

---- Metadata out - Exif SubIFD---
New Subfile Type : Full-resolution image
Image Width : 5584 pixels
Image Height : 3728 pixels
Bits Per Sample : 14 bits/component/pixel
Compression : Uncompressed
Photometric Interpretation : Color Filter Array
Strip Offsets : 2267136
Samples Per Pixel : 1 samples/pixel
Rows Per Strip : 3728 rows/strip
Strip Byte Counts : 41634304 bytes
X Resolution : 300 dots per inch
Y Resolution : 300 dots per inch
Planar Configuration : Chunky (contiguous for each subsampling pixel)
Resolution Unit : Inch
CFA Repeat Pattern Dim : 2 2
CFA Pattern : [Red,Green][Green,Blue]
Unknown tag (0x9217) : 2

And the preview?

Yes, exiftool tell me there are a PreviewIFD

---- ExitTool out - PreviewIFD ----
Compression                     : JPEG (old-style)
X Resolution                    : 300
Y Resolution                    : 300
Resolution Unit                 : inches
Preview Image Start             : 52164
Preview Image Length            : 124762
Y Cb Cr Positioning             : Co-sited
Preview Image                   : (Binary data 124762 bytes, use -b option to extract)

Best