rotating a bmp file using C++ ?

Question

1.00/5 (1 vote)

See more:

C++

#include<iostream>
#include<fstream>
#include<string>
using namespace std;

int main()
{
	fstream flower("flower.bmp", ios::in | ios::out | ios::binary);
	int width=686;
	int height=800;
	flower.seekg(18,ios::beg);
	flower.put(height);
	flower.seekg(4);
	flower.put(width);
	
	flower.close();
}

Posted 21-Feb-15 11:10am

Alexis i

Updated 21-Feb-15 11:15am

v3

Add a Solution

Comments

Alexis i 21-Feb-15 17:16pm

i want to rotate a bmp file named flower 90 degrees, so according to the BMP bitmap file format i have changed the 18th byte to 800 and the 22nd byte to 686 which swaps the height and width, but the image is corrupted! can anyone help me?

Sergey Alexandrovich Kryukov 21-Feb-15 22:12pm

How about thinking just a bit, at least a tiny bit?
—SA

2 solutions

Solution 2

Just exchanging width and height will not rotate the image. You also need to rotate the bitmap data pixel by pixel. That requires quite a bit of buffer handling and data shoveling. For an example how to do it, look here:

Add fast user-extensible image processing support to CBitmap[^]

Posted 21-Feb-15 12:04pm

nv3

Comments

Sergey Alexandrovich Kryukov 21-Feb-15 22:12pm

Sure, a 5.
—SA

Sergey Alexandrovich Kryukov 21-Feb-15 22:31pm

I found inquirer's confusion so amazing that I added a simple example to illustrate this "corruption". Please see Solution 3.
—SA

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)

Sergey Alexandrovich Kryukov · Accepted Answer · 2015-02-21T16:23:00

I was afraid that my suggestion to "think a bit" could possibly offend you a bit, so I probably have to illustrate what this thinking could mean.

Suppose you have some bit data, which tells you (forget the "format", it is irrelevant):
you have
width = 3, height = 2, and pixels data 123456
It means that first line is 123 and the second line is 456:

123
456

If you swap width and height, you would have

width = 2, height = 3:
12
34
56

But turn original picture 90° clockwise (you can just turn your computer screen 90° clockwise and look at the same numbers), what will you see? apparently,

41
52
63

and counterclickwise:

36
25
14

The last two images are correct, and the previous one is "corrupted". What could be not obvious here?
This is what nv3 meant by telling you "to rotate the bitmap data pixel by pixel".

I hope now the problem should be clear to you.

—SA