Extracting preview Image from PEF RAW file

[BogdanH]

You can take this here from DPReview:
http://movies.dpreview.com.s3.amazonaws.com/pentax_k5/IMGP3854.DNG.zip

I just did that and here (again) I get nothing from this file by using:
exiftool -b -BigImage -w %f.jpg IMGP3854.DNG
-and BigImage also isn't listed in Composite (I have latest ExifTool v8.95). Now I am really getting curious 

Bogdan

[Beholder3]

Huh?
I just upgraded to 8.95 but still I get the BigImage using exiftoolGUI.


Using Windows 7 64bit Ultimate, exiftoolGui 5.14 and exiftool 8.95.

[Beholder3]

One question to Phil as add on:
Does that actually mean, these files (DNG/PEF) really do contain the same fullsize "preview" JPG twice, each stored in a different "area"? or is it only two "pointers" pointing to the same JPGs?

[Phil Harvey]

The Composite BigImage tag is just a duplicate of the biggest JPG image in the file.

There are 2 PreviewImage's in the DNG, but they are different (different resolutions and file sizes).

Regarding the BigImage confusion:  This is one of the user-defined tags in the sample config file.  So Beholder3 must have the sample config file installed.

- Phil

[BogdanH]

I've downloaded ExifTool again, deleted "par" directory in Temp, and ran above command again -same result: BigImage isn't there. To be sure, I've executed command in console too. Otherwise, same GUI version, and Win7 x64.
Are we using the same IMGP3854.DNG image? I mean, this IS weird.

Bogdan

[Beholder3]

Regarding the BigImage confusion:  This is one of the user-defined tags in the sample config file.  So Beholder3 must have the sample config file installed.

Ah, yes.  Just checked it. I must have inserted the code into the config file some months ago when I first played around with the preview extraction. I forgot about it and assumed its "standard".

That is the code in .ExifTool_config

Code Select Expand


# [advanced] select largest JPEG preview image
        BigImage => {
        Desire => {
            0 => 'JpgFromRaw',
            1 => 'PreviewImage',
            2 => 'OtherImage',
            # (DNG and A100 ARW may be have 2 PreviewImage's)
            3 => 'PreviewImage (1)',
                },
        # ValueConv may also be a code reference
        # Inputs: 0) reference to list of values, 1) ExifTool object
        ValueConv => sub {
            my $val = shift;
            my ($image, $bigImage, $len, $bigLen);
            foreach $image (@$val) {
            next unless ref $image eq 'SCALAR';
            # check for JPEG image (or "Binary data" if -b not used)
            next unless $$image =~ /^(\xff\xd8\xff|Binary data (\d+))/;
            $len = $2 || length $$image; # get image length
            # save largest image
            next if defined $bigLen and $bigLen >= $len;
            $bigLen = $len;
            $bigImage = $image;
                    }
            return $bigImage;

[BogdanH]

That explains a lot  Thank you.

Bogdan

[Beholder3]

Sorry. I found one more thing in this DNG:

---- ExifTool ----
ExifTool Version Number         : 8.95
---- File ----
File Name                       : IMGP3854.DNG
Directory                       : .
File Size                       : 22 MB
File Modification Date/Time     : 2010:12:16 18:50:58+01:00
File Permissions                : rw-rw-rw-
File Type                       : DNG
MIME Type                       : image/x-adobe-dng
Exif Byte Order                 : Big-endian (Motorola, MM)
---- EXIF ----
Subfile Type                    : Reduced-resolution image
Image Width                     : 160
Image Height                    : 120

For one there seems to be no such preview file in there which should be extractable, as we learned there are no real small thumbnails in there in the DNG.

For two in the output at the same time I can find nothing about a Reduced resolution image with 640 x 480 which is actually extractable.

I see three options:

a) There is a mini 160x120 preview which we cant yet extract plus there is a 640x480 preview which doesnt show in exiftools output in detail
b) there is a mini 160x120 preview in there and it is being saved in a blown up way (dont really believe this)
c) exiftool misinterprets the dimensions by factor 4.

[Phil Harvey]

The option is a).

The 160x120 preview is not extracted by ExifTool because it is not JPEG format.  (Look at the Compression tag)

- Phil