Title: Exif DigitalZoomRatio tag meaning and use
Post by: 11august on November 18, 2021, 06:13:47 AM
Post by: 11august on November 18, 2021, 06:13:47 AM
Hey guys :)
Is anyone knows what does the exif.digital.zoom.ratio tag exactly measure? We thought it should be a factor used to multiply the focal length, but, doing that, angular measurements on pictures give erratic results.
Also, I know that most of the Smartphone as for now use composite zoom, but I've found some 'old' compact cameras that use composite zooms as well, like the Samsung WB690. It says in the technical specs "Digital zoom x4", "optical zoom x18", but I can't find any logic in the use of the DigitalZoomRatio. I thought that, logically, at first the optical zoom is used and then, the digital zoom above x18, but looking at the results of the data of the extracted tags, I'm not that sure... Is there a way by solely looking at the exif what zoom was used?
Attached two photos of the sun taken with the WB690, one with a 1.00 zoom and the other with a 2.80 zoom.
Thanks!
Is anyone knows what does the exif.digital.zoom.ratio tag exactly measure? We thought it should be a factor used to multiply the focal length, but, doing that, angular measurements on pictures give erratic results.
Also, I know that most of the Smartphone as for now use composite zoom, but I've found some 'old' compact cameras that use composite zooms as well, like the Samsung WB690. It says in the technical specs "Digital zoom x4", "optical zoom x18", but I can't find any logic in the use of the DigitalZoomRatio. I thought that, logically, at first the optical zoom is used and then, the digital zoom above x18, but looking at the results of the data of the extracted tags, I'm not that sure... Is there a way by solely looking at the exif what zoom was used?
Attached two photos of the sun taken with the WB690, one with a 1.00 zoom and the other with a 2.80 zoom.
Thanks!
Title: Re: Exif DigitalZoomRatio tag meaning and use
Post by: Phil Harvey on November 18, 2021, 08:31:37 AM
Post by: Phil Harvey on November 18, 2021, 08:31:37 AM
I measure 302 pixels across the solar disk in S1, and 890 pixels for S2. 890/302 = 2.94 -- not to far from 2.80, given the inaccuracy of the measurement due to atmospheric distortions since the pictures were taken at different times.
- Phil
- Phil
Title: Re: Exif DigitalZoomRatio tag meaning and use
Post by: 11august on November 18, 2021, 09:58:54 AM
Post by: 11august on November 18, 2021, 09:58:54 AM
Thank you Phil for your reply. Makes sense.
However, I still don't get how to relate this with the Focal Length and Focal Length eq 35mm in the EXIF. Between the two photos you have ~2.8 ratio for the zoom as shown in the DigitalZoomRatio tag but you have ~1.4 ratio for the Focal Length and Focal Length eq 35mm. Why the x2 difference?
I've taken for example some night shots of the moon (angular size: 0.5°) with a Samsung SM-A217F (Galaxy A21s) at various zoom levels and extracted the Focal Length related tags. The DigitalZoomRatio tag varies apparently accordingly to the zoom (from 1.00 to 10.00) but not the Focal Length (4.60 and 25.00 in eq 35 mm). I can understand that if only the Digital zoom is used (Focal Length tags only rely on optical zoom), but then how can we correctly use the Focal Length data to do angular measurements?
Thanks again for your help!
However, I still don't get how to relate this with the Focal Length and Focal Length eq 35mm in the EXIF. Between the two photos you have ~2.8 ratio for the zoom as shown in the DigitalZoomRatio tag but you have ~1.4 ratio for the Focal Length and Focal Length eq 35mm. Why the x2 difference?
I've taken for example some night shots of the moon (angular size: 0.5°) with a Samsung SM-A217F (Galaxy A21s) at various zoom levels and extracted the Focal Length related tags. The DigitalZoomRatio tag varies apparently accordingly to the zoom (from 1.00 to 10.00) but not the Focal Length (4.60 and 25.00 in eq 35 mm). I can understand that if only the Digital zoom is used (Focal Length tags only rely on optical zoom), but then how can we correctly use the Focal Length data to do angular measurements?
Thanks again for your help!
Title: Re: Exif DigitalZoomRatio tag meaning and use
Post by: Phil Harvey on November 18, 2021, 01:39:12 PM
Post by: Phil Harvey on November 18, 2021, 01:39:12 PM
You can answer these questions better than I can since you own this camera. I don't own a camera a the produces this tag, so I can't test it out myself. Only the manufacturer knows for sure what this tag means.
- Phil
- Phil