Check a JPEG is progressive or baseline

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Determine progressive JPEG by it’s content

From wiki-JPEG, we could see a baseline/progressive JPEG have byte marker mapping differently as following:

Short name Bytes Payload Name
SOF0 0xFF, 0xC0 variable size Start Of Frame (baseline DCT)
SOF2 0xFF, 0xC2 variable size Start Of Frame (progressive DCT)

So to tell the image is progressive JPEG, we need to check if it contains 0xFF, 0xC0 which is c2ff in Two-byte hexadecimal display.

Check a local JPEG is progressive by hexdump

We could use hexdump to display image contents in Two-byte hexadecimal display format, then grep to check if it contains c2ff which is progressive only marker

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$ hexdump -x progressive.jpg | grep c2ff
0000090    1414    1414    1414    1414    1414    1414    1414    c2ff
# find c2ff so it is progressive!

$ hexdump -x baseline.jpg | grep c2ff
# no c2ff in baseline

$ hexdump -x baseline.jpg | grep c0ff
0000090    1414    1414    1414    1414    1414    1414    1414    c0ff
# baseline has c0ff

Check an image url is progressive curl, hexdump and grep

We could use curl to fetch an image, then hexdump to show it in Two-byte hexadecimal display format, then grep to check if it contains c2ff, in short, curl <url> | hexdump -x | grep c2ff

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$ curl https://www.paddingleft.com/2018/09/04/check-a-JPEG-is-progressive-or-baseline/progressive.jpg | hexdump -x | grep c2ff
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 47144  100 47144    0     0   118k      0 --:--:-- --:--:-- --:--:--  118k
0000090    1414    1414    1414    1414    1414    1414    1414    c2ff
# find c2ff so it is progressive!

Material

Here I got one progressive JPEG and one baseline JPEG for you to test :)

Progressive JPEG

Baseline JPEG