How to know coordinates in a real image from a scaled image.

Posted by ocell on Stack Overflow See other posts from Stack Overflow or by ocell
Published on 2010-06-07T09:48:47Z Indexed on 2010/06/07 9:52 UTC
Read the original article Hit count: 329

Filed under:

c++

|

image

|

qt

|

coordinates

|

maths

Hi folks,

First of all thanks for your time reading my question :-)

I have an original image (w': 2124, h': 3204) and the same image scaled (w: 512, h: 768). The ratio for width is 4.14 (rw) and the ratio for height is 4.17 (rh).

I'm trying to know the coordinates (x', y') in the original image when I receive the coordinates in the scaled image (x, y). I'm using the formula: x' = x * rw and y' = y * rh. But when I'm painting a line, or a rectangle always appears a shift that is incremented when x or y is higher.

Please anybody knows how to transform coordinates without loosing of accuracy.

Thanks in advance! Oscar.

© Stack Overflow or respective owner

Related posts about c++

Which C++ book shold I get between "C++ Primer" vs "C++ Primer Plus"

as seen on Stack Overflow - Search for 'Stack Overflow'
I want to learn C++ by using Vim and MinGW as compiler. I'm interesting at "C++ Primer (4th Edition)" and "C++ Primer Plus (5th Edition)" but I don't know how about it different. It has no book store that I can review those books, so I want to know, what is the different between those book and which… >>> More
C++ : C++ Primer (Stanley Lipmann) or The C++ programming language (special edition)

as seen on Stack Overflow - Search for 'Stack Overflow'
I have a Computer Science degree (long2 time ago) .. I do know Java OOP but i am now trying to pick up C++. I do have C and of course data structure using C or pascal. I have started reading Bjarne Stroustrup book (The C++ Programming Language - Special Edition) but find it extremely difficult esp… >>> More
I need help on my C++ assignment using MS Visual C++

as seen on Stack Overflow - Search for 'Stack Overflow'
Ok, so I don't want you to do my homework for me, but I'm a little lost with this final assignment and need all the help I can get. Learning about programming is tough enough, but doing it online is next to impossible for me... Now, to get to the program, I am going to paste what I have so far. This… >>> More
Managed c++ std::string not accessible in unmanaged c++

as seen on Stack Overflow - Search for 'Stack Overflow'
In unmanaged c++ dll i have a function which takes constant std::string as argument Prototype : void read ( const std::string &imageSpec_ ) I call this function from managed c++ dll by passing a std::string. When i debug the unmanaged c++ code the parameter imageSpec_ shows the value correctly… >>> More
The Definitive C++ Book Guide and List

as seen on Stack Overflow - Search for 'Stack Overflow'
After more than a few questions about deciding on C++ books I thought we could make a better community wiki version. Providing QUALITY books and an approximate skill level. Maybe we can add a short blurb/description about each book that you have personally read / benefited from. Feel free to debate… >>> More

Related posts about image

Image anotation (Highlighting parts of an image, Scrubbing an image) using Javascript

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, We are working on an application and would like users to annotate an image. By annotation I mean, the ability to highlight parts of an image. Once the image is highlighted, and submit is clicked, the highlighted attributes (color, area highlighted) are submitted to the server to be stored in… >>> More
How I can add JScroll bar to NavigableImagePanel which is an Image panel with an small navigation vi

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, I have the following NavigableImagePanel, it is under BSD license and I found it in the web. What I want to do with this panel is as follow: I want to add a JScrollPane to it in order to show images in their full size and let the users to re-center the image using the small navigation panel… >>> More
Twitter Bootstrap styling conflicts with plug-ins like jqGrid and other third part libraries

as seen on Geeks with Blogs - Search for 'Geeks with Blogs'
Issues:The concern is that the Twitter Bootstrap framework is that some of their css selectors are simply too generic and have incompatibility issues and conflicts with most third party plug-ins and css libraries, like jQuery-UI and jqGrid.My most pressing concern is only with the generic selector… >>> More
PHP invalid image's and error handling

as seen on Stack Overflow - Search for 'Stack Overflow'
Using PHP's Image and GD functions you can use the following method to finally output the php image imagepng($image); Sometimes, for whatever reason the image may not be displayed typically the error is not with the image but with the actual php functions not executing successfully. However this… >>> More
apt-get install was interrupted

as seen on Ask Ubuntu - Search for 'Ask Ubuntu'
I am new to Ubuntu. I got the following lines after an interrupted apt-get install. Running depmod. update-initramfs: deferring update (hook will be called later) Examining /etc/kernel/postinst.d. run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 3.13.0-29-generic /boot/vmlinuz-3.13.0-29-generic run-parts:… >>> More