image processing in c#

Question

before question think about for example photoshop. When you draw a rectangle on the picture.You can move it. And when you move it works very quickly and it doeasnt make some traces on the picture.
So my question is, how to do that in c# application?

Answer 1

This might be useful for you

Image Processing for Dummies with C# and GDI+ Part 1 - Per Pixel Filters
Image Processing for Dummies with C# and GDI+ Part 2 - Convolution Filters
Image Processing for Dummies with C# and GDI+ Part 3 - Edge Detection Filters
Image Processing for Dummies with C# and GDI+ Part 4 - Bilinear Filters and Resizing
Image Processing for Dummies with C# and GDI+ Part 5 - Displacement filters, including swirl
Image Processing for Dummies with C# and GDI+ Part 6 - The HSL color space

Answer 2

When you are moving the rectangle, Photoshop doesn't put it in the image and then draw the image, instead the image is drawn without the rectangle, and the rectangle is drawn on top of that on the screen. That way when you move the rectangle it can redraw the part of the image that previously was covered by the rectangle, and draw the rectangle at the new position.

Answer 3

I think you're asking about selection rectangles (or other temporary shapes) on top of the document image. This effect is sometimes known as “rubber banding”, especially when drawing a line from one point to another (it stretches like a rubber band).

Traditionally, this was done by using XOR drawing -- instead of overwriting the image with the selection shape, the colors in that area are inverted. Then, to remove the selection, it suffices to invert the colors again, returning to the same original image. Today, graphics rendering is fast enough that such tricks are not usually necessary; it suffices to simply repaint that part of the window (without the rectangle).

Either way, it is important to recognize that the document image — the image the user is editing — is not the same as the window image, which is just a copy to be remade whenever necessary. In the window, the document image is drawn and then selections, guide marks, and other such controls are drawn on top of it.

I'm not familiar with C#'s GUI facilities (and I understand there is more than one GUI framework you might be using), but it's probably got the usual structure of putting many "widgets", "views", or "controls" in the window (possibly nested inside each other). You can do a straightforward selection box — though not an optimally efficient one — by just putting an appropriately sized rectangle widget (with a solid border and a transparent background) on top of an image widget. This lets your GUI framework take care of the appropriate redrawing for you and is probably a good cheap way to start.