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ExifTool FAQ
By default, ExifTool applies a print conversion (PrintConv) to extracted information to make the output more human-readable. Some conversions involve lookup tables which are documented in the Values column of the tag name documentation. For example, the GPSAltitudeRef tag defines the following conversions:
0 = Above Sea Level
1 = Below Sea Level


For this tag, a value of '0' is printed as 'Above Sea Level', and '1' is printed as 'Below Sea Level'. Reading and writing with ExifTool is symmetrical [with the possible exception of list-type tags -- see FAQ number 17 below], so a value that is printed as 'Above Sea Level' must also be written in that form. (In other words, the inverse print conversion is applied when writing values.) For example, to write GPSAltitudeRef you can type:
<code class="language-bash">exiftool -gpsaltituderef="Above Sea Level" image.jpg</code>

or any unambiguous short form may be used and ExifTool will know what you mean, eg)
<code class="language-bash">exiftool -gpsaltituderef=above image.jpg</code>

Alternatively, the print conversion can be disabled for all tags with the -n option, or for individual tags by suffixing the tag name with a '#' character. In either case the printed value of GPSAltitudeRef will be '0' or '1' when extracting information, and the value is written in the same way. So following two commands have exactly the same effect as above:
<code class="language-bash">exiftool -gpsaltituderef=0 -n image.jpg
exiftool -gpsaltituderef#=0 image.jpg</code>
exiftool  errormessage  gps  geo  exif  jpeg  jpg  solution 
2 days ago by kme
Copy GPS coord tags - Wrong Hemisphere!
Add -g1 to last command to see the source of the various GPS tags.


This didn't actually help me; what helped was including *all* the tags that had to do with GPS, except the time/datestamps. I came up with this Bash function to help

<code class="language-bash"># copy EXIF GPS info including altitude from one file to another
exif_gps_from_to() {
exiftool -n -tagsFromFile "$1"\
-GPSVersionID \
-GPSLatitudeRef \
-GPSLongitudeRef \
-GPSAltitudeRef \
-GPSAltitude \
-GPSLongitude \
-GPSLatitude \
-GPSPosition \
"$2"
}
</code>
exif  jpg  jpeg  imageprocessing  gps  geo  exiftool  commandline  solution 
2 days ago by kme
Unraveling The JPEG
JPEG images are everywhere in our digital lives, but behind the veil of familiarity lie algorithms that remove details that are imperceptible to the human eye. This produces the highest visual quality with the smallest file size—but what does that look like? Let's see what our eyes can't see!
jpeg  fileformat 
15 days ago by tiredoldfellow
Faster Neural Networks Straight from JPEG | Uber Engineering Blog
In this article, we describe an approach presented at NeurIPS 2018 for making CNNs smaller, faster, and more accurate all at the same time by hacking libjpeg and leveraging the internal image representations already used by JPEG, the popular image format.
cnn  machine-learning  media  image  jpeg 
19 days ago by peterb
Unraveling The JPEG
very good interactive explanation of how jpeg works
image  pedagogy  compression  jpeg 
23 days ago by aparrish

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