C / C++ / MFC

5-Feb-07 5:45

I have a program that analyses bitmap and at the moment i am using getPIxel and setPixel, as you will know if you have used them they are very slow. Does any one know of an alternative that will increase the speed?

Waldermort5-Feb-07 6:16

5-Feb-07 6:16

Use a DIB and access the bits directly. This will be especially fast when you need to get a lot of pixels since you won't need to recalculate the pixel's offset and convert to a DWORD each time.

ceejeeb5-Feb-07 6:33

5-Feb-07 6:33

Im not too sure what you mean by "recalculate the pixel's offset and convert to a DWORD each time" because i dont think im doing that now. This is my code it compares each pixel in the 2 dc's :

<br />
for (int w = 0; w < width; w++)<br />
	{<br />
	   for (int h = 0; h < height; h++)<br />
	   {<br />
		  if (GetPixel(hdcOld, w, h) != GetPixel(hdcNew, w, h))<br />
		  {<br />
			SetPixel(dcNew, w, h, RGB(255, 255, 255));<br />
			pixelCount++;<br />
		  }<br />
		  else<br />
		  {<br />
			 SetPixel(dcNew, w, h, RGB(0, 0, 0));<br />
		  }<br />
	   }<br />
	}<br />

Waldermort5-Feb-07 6:56

5-Feb-07 6:56

Maybe you are not doing it yourself, but what do you thing GetPixel() is doing internally? Each time you call it, it must first read the header, get the bits, calculate the size of a pixel, calculate the the size of a row, calculate which row, calculate how far into that row, get the pixel, convert it to a COLORREF then give it back to you. ALL FOR ONE PIXEL! This is for every single call.

If you use a dib, you can do all that calculating yourself and do it only once.

ceejeeb5-Feb-07 6:58

5-Feb-07 6:58

So how would i do it using dib, im pretty new to c++?

Waldermort5-Feb-07 7:12

5-Feb-07 7:12

have a search of the GDI and bitmap articles, there are quite a few DIB wrappers available.

ceejeeb5-Feb-07 7:55

5-Feb-07 7:55

Ok so i have put my bitmaps in DIB's and placed them in seperate dc's but what function do i use now instaed of getPixel()?

Waldermort5-Feb-07 9:11

How to call method inside another method..

5-Feb-07 9:11

There is no specific function. If you have downloaded and integrated one of the DIB wrapper classes, derive a new class from it and add a new member.

Lets say you are scanning a web-cam image and you want to get every 10th pixel. In your new function, get the images-bits from the base class which is just one big array of pixels. Calculate the bitmaps paramaters, then in a loop calculate which pixels you want ( y * bitmapwidth_inbytes + x ) and read them from the array.

Just remember, with a DIB, the pixels are not always a 32 value like you get back from GetPixel. They could be:
1 Bits ( 0 == black, 1 == white )
4 Bits ( 1 byte with two indexes into the color table )
8 Bits ( an array of bytes each representing an index into the color table )
16 Bits ( an array of WORD each representing an index into the color table )
24 Bits ( an array of DWORD look on MSDN for RGBQUAD )
32 Bits ( an array of DWORD look on MSDN for RGBQUAD )
64 Bits ( only windows vista supports these I think )

By far, the easiest to deal with are 24 and 32 bit images, all of the others use a color table. If you need the actual COLORREF value, then you must calculate it from whatever value you get from the array.

Shah Satish5-Feb-07 4:44

5-Feb-07 4:44

Hi !!

I have one main method and now i want to call this main method in another method..

for example...

void NORMAL()
{


}

void MAJOR ()
{

  Here i want to call void NORMAL() method 
}

In void MAJOR () method, I want to call void NORMAL ()..

how can i call it ??

Both are in same .cpp file..n i have no class.

Thanking you..

Shah

Maximilien5-Feb-07 5:01

Maximilien

5-Feb-07 5:01

what about :

void MAJOR()
{
 NORMAL();
}

This is rrrreeeaaallllyyyy basic stuff, or I did not understood the question.

Maximilien Lincourt
Your Head A Splode - Strong Bad

Shah Satish5-Feb-07 5:09

5-Feb-07 5:09

oppsss..Really really sorry.. i have Problem in my code..

Maximilien5-Feb-07 8:20

Maximilien

5-Feb-07 8:20

and what might be the problem ?

Maximilien Lincourt
Your Head A Splode - Strong Bad

benjymous5-Feb-07 5:04

benjymous

5-Feb-07 5:04

void MAJOR ()
{
  NORMAL();
}

Come on, this is really beginner stuff! Aren't you calling your MAJOR() function from somewhere else? Where's it getting called from?

Shah Satish5-Feb-07 5:09

5-Feb-07 5:09

oppsss..Really sorry..Problem in my code..

Hamid_RT5-Feb-07 7:53

Hamid_RT

5-Feb-07 7:53

Is this a specifc question or simple question? Wink | ;)

WhiteSky

Shah Satish5-Feb-07 7:55

5-Feb-07 7:55

Heee heee..This is not Specific nor Simple.. but its stupid question..Actually i tried same code but it was not working.. problem was in my code but in method.