Plain text GIF resolution

Question

0.00/5 (No votes)

See more:

Well, the thing is that in Linux with the Terminal I use nano to create a plain text file with the content "GIF89a2017" and I save it as rare and I know that due to that header the file is detected as a GIF image. The thing is that four bytes that I put next to the header, 2017 in this case, give the resolution. That way when I do the command file rare it outputs: rare.gif: GIF image data, version 89a, 12338 x 14129.

What I have tried:

I know that those four bytes are some unsigned 16-bit integers but I don't know how it is done to convert 20 into 0x3032 and 17 into 0x3731. That way you get the resolution but I don't know how you get it, to me it just seems like a 3 is added.

Thanks to everyone!

Posted 19-Oct-17 8:54am

Member 13474534

Updated 19-Oct-17 9:35am

Add a Solution

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Richard MacCutchan · Answer 1 · 2017-10-19T09:22:00

0x3032 is the hex representation of the characters '02' stored in a short. And (assuming this is on an x86 system) that will actually be seen as the two characters '20' when addressed as bytes. Similarly 0x3731 is the characters 71, or 17 in normal order.

To store those two values as integers you need to put 20 as hex 0x0014) and 17 as hex 0x0011. So your header needs to be "GIF89a\x00\x14\x00\x11"; where the \x prefix indicates an absolute hex value not the four character \x00 etc.. But quite how you expect to create a GIF image with a text editor is something that you may find even more challenging.