[libcamera-devel] [PATCH v3] utils: raspberrypi: ctt: dng_load_image: Work with DNG files from Picamera2

[Laurent Pinchart]

Hi William,

Thank you for the patch.

On Wed, Aug 03, 2022 at 09:25:39AM +0100, William Vinnicombe via libcamera-devel wrote:
> From: William Vinnicombe <william.vinnicombe at raspberrypi.com>
> 
> The DNG specification is based on the TIFF file format and recommends
> storing the raw image data in a SubIFD and the Exif tags in an Exif IFD.
> Other options are allowed, even if not recommended, such as storing both
> the raw image data and the Exif data in IFD0, as done by the TIFF/EP
> specification.
> 
> libcamera-apps use pyexiv2 to produce DNG files, following the DNG
> recommendation, while applications based on picamera2 use PiDNG, which
> adopts the TIFF/EP structure. Why it does so is not currently clear (see
> https://github.com/schoolpost/PiDNG/issues/65 for discussions on this
> topic), but as files based on the DNG and TIFF/EP variants exist in the
> wild, both need to be supported by ctt.
> 
> Add code to identify which tags are being used, and then load the
> metadata from the correct tags.
> 
> Signed-off-by: William Vinnicombe <william.vinnicombe at raspberrypi.com>
> Reviewed-by: David Plowman <david.plowman at raspberrypi.com>
> Reviewed-by: Naushir Patuck <naush at raspberrypi.com>

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

> ---
>  utils/raspberrypi/ctt/ctt_image_load.py | 32 +++++++++++++++++++------
>  1 file changed, 25 insertions(+), 7 deletions(-)
> 
> diff --git a/utils/raspberrypi/ctt/ctt_image_load.py b/utils/raspberrypi/ctt/ctt_image_load.py
> index 934db123..7f8ba72a 100644
> --- a/utils/raspberrypi/ctt/ctt_image_load.py
> +++ b/utils/raspberrypi/ctt/ctt_image_load.py
> @@ -301,17 +301,35 @@ def dng_load_image(Cam, im_str):
>          metadata.read()
>  
>          Img.ver = 100  # random value
> -        Img.w = metadata['Exif.SubImage1.ImageWidth'].value
> +        """
> +        The DNG and TIFF/EP specifications use different IFDs to store the raw
> +        image data and the Exif tags. DNG stores them in a SubIFD and in an Exif
> +        IFD respectively (named "SubImage1" and "Photo" by pyexiv2), while
> +        TIFF/EP stores them both in IFD0 (name "Image"). Both are used in "DNG"
> +        files, with libcamera-apps following the DNG recommendation and
> +        applications based on picamera2 following TIFF/EP.
> +
> +        This code detects which tags are being used, and therefore extracts the
> +        correct values.
> +        """
> +        try:
> +            Img.w = metadata['Exif.SubImage1.ImageWidth'].value
> +            subimage = "SubImage1"
> +            photo = "Photo"
> +        except KeyError:
> +            Img.w = metadata['Exif.Image.ImageWidth'].value
> +            subimage = "Image"
> +            photo = "Image"
>          Img.pad = 0
> -        Img.h = metadata['Exif.SubImage1.ImageLength'].value
> -        white = metadata['Exif.SubImage1.WhiteLevel'].value
> +        Img.h = metadata[f'Exif.{subimage}.ImageLength'].value
> +        white = metadata[f'Exif.{subimage}.WhiteLevel'].value
>          Img.sigbits = int(white).bit_length()
>          Img.fmt = (Img.sigbits - 4) // 2
> -        Img.exposure = int(metadata['Exif.Photo.ExposureTime'].value*1000000)
> -        Img.againQ8 = metadata['Exif.Photo.ISOSpeedRatings'].value*256/100
> +        Img.exposure = int(metadata[f'Exif.{photo}.ExposureTime'].value*1000000)
> +        Img.againQ8 = metadata[f'Exif.{photo}.ISOSpeedRatings'].value*256/100
>          Img.againQ8_norm = Img.againQ8 / 256
>          Img.camName = metadata['Exif.Image.Model'].value
> -        Img.blacklevel = int(metadata['Exif.SubImage1.BlackLevel'].value[0])
> +        Img.blacklevel = int(metadata[f'Exif.{subimage}.BlackLevel'].value[0])
>          Img.blacklevel_16 = Img.blacklevel << (16 - Img.sigbits)
>          bayer_case = {
>              '0 1 1 2': (0, (0, 1, 2, 3)),
> @@ -319,7 +337,7 @@ def dng_load_image(Cam, im_str):
>              '2 1 1 0': (2, (3, 2, 1, 0)),
>              '1 0 2 1': (3, (1, 0, 3, 2))
>          }
> -        cfa_pattern = metadata['Exif.SubImage1.CFAPattern'].value
> +        cfa_pattern = metadata[f'Exif.{subimage}.CFAPattern'].value
>          Img.pattern = bayer_case[cfa_pattern][0]
>          Img.order = bayer_case[cfa_pattern][1]
>  

-- 
Regards,

Laurent Pinchart