JPEG Sise For Emergency Communications
JPEG SIZES FOR TRANSMISSION BY RADIO
I have experimented with jpg sizes and resolutions for possible transmission of .jpg files from remote sites to stations with network connections to the Emergency Operations Center. What I was looking for was small file size of a jpg that still had enough detail to be useful.
I started with a full size picture of WA9IGK's vehicle. This image is about 3000x2000 pixels and the jpg file was about 2.2 Mbyte. A file this large would use too much time and bandwidth at speeds of 19KBaud or slower, but has more than enough resolution for most emergency purposes.
I shrank the picture using a linux utility call “convert.” The command line is below:thumb.256x256.wa9igk.pontia
convert -size 120x120 wa9igk.pontiac.jpg -resize 120x120 thumb.wa9igk.pontiac.jpg
The resulting thumbnail looked just fine viewed at its natural size of 120x120 pixels, but when enlarged 600% so someone could see detail, the detail was pixelated and missing. The file size was 16 Kbyte.
Next I tried 256x256 pixels:
convert -size 256x256 wa9igk.pontiac.jpg \
-resize 256x256 thumb.256x256.wa9igk.pontiac.jpg
The resulting thumbnail is slightly over twice the size in each dimension but has over four times the information. This thumbnail proved to be satisfactory for enlarging and viewing detail. For example the license plate call letters are clearly readable. The file size was 30 Kbyte. Interestingly we get 4 times the picture size when the file is only twice as large. A picture this large will take only about 30 seconds to transmit at 9600 Baud effective throughput.
wa9igj.pontiac.jpg
thumb.wa9igj.pontiac.jpg
thumb.256x256.wa9igj.pontiac.jpg
