dng_validate - Missing or invalid SamplesPerPixel

[shakesbeery]

Hi all,

I'm working on a program to wrap image info into a dng format, but have run into a snag that I cannot find in the documentation. I'll start off with the verbose output of dng_validate:

    Uses little-endian byte order

    Magic number = 42

    IFD 0: Offset = 8, Entries = 20

    NewSubFileType: Preview Image

    ImageWidth: 62

    ImageLength: 41

    BitsPerSample: 8 8 8

    Compression: Uncompressed

    PhotometricInterpretation: RGB

    Make: "Test Program"

    Model: "V1"

    StripOffsets: Offset = 386

    Orientation: 1 - 0th row is top, 0th column is left

    SamplesPerPixel: 3

    RowsPerStrip: 41

    StripByteCounts: Count = 7626

    PlanarConfiguration: 1

    Software: "Test"

    DateTime: 1900:01:01 00:00:00

    SubIFDs: IFD = 8012

    DNGVersion: 1.4.0.0

    DNGBackwardVersion: 1.1.0.0

    UniqueCameraModel: "Test Program"

    NextIFD = 0

    SubIFD 1: Offset = 8012, Entries = 10

    NewSubFileType: Main Image

    ImageWidth: 1000

    ImageLength: 667

    BitsPerSample: 16 16 16

    Compression: Uncompressed

    PhotometricInterpretation: LinearRaw

    StripOffsets: Offset = 8144

    SamplesPerPixel: 3

    RowsPerStrip: 667

    StripByteCounts: Count = 4002000

    NextIFD = 0

*** Error: Missing or invalid SamplesPerPixel (SubIFD 1) ***

So obviously SamplesPerPixel is present in SubIFD 1, and I've seen plenty of dngs that have LinearRaw with 3 channels. The image won't open in photoshop or in lightroom and I can't find any indication as to what the actual problem is. Help greatly appreciated. Thanks.

[sandy_mc]

Your DNG is missing a whole lot of required tags. The specific error is probably because there aren't color matrixes, and I think that DNG_validate uses the size of the color matrixes to work out how many color planes there are. SamplesPerPixel of three only makes sense for three color planes.

[shakesbeery]

Thanks for the reply. ColorMatrix1 was definitely missing, and its addition now passes dng_validate. Is there a reference for how the color matrix is calculated? In some use cases, I'm storing demosaicized RGB images in DNG as a temporary container, but they appear white-washed when opened.

[sandy_mc]

There's whole chapter in the DNG specification on how the matrixes, etc work. You can download it from the Adobe website.