reversing pixels in BMP to opposite with simple loop

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im not really here

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Joined: 14th Oct 2010

Location: iowa

Posted: 9th Nov 2010 11:48

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hello i am trying to take an image.bmp display it and cycle threw it pixel by pixel using a loop like so

+ Code Snippet


  int width=dbBitmapWidth(0);
  int height=dbBitmapHeight(0);
	
        dbLoadImage("cow.bmp",1);
	dbCenterText(320,240," COLOR SWAP!");
	dbPasteImage(1,0,0,0);
	DWORD pixelColor;
	DWORD blue = dbRGB(0,0,255);
    DWORD green = dbRGB(0,255,0);
    DWORD red = dbRGB(255,0,0);
for (int y=0;y<width;y++)
   
   
{
	for(int x=0;x<height;x++){
pixelColor=dbPoint(x,y);
if   //////////////////////////im stuck right here
     ///////////////////////im not sure how to swap from the
     //////////////////////RGB red value to its blue
     ////////////////////for example
    ////////////////////RGB value of (230, 100, 98)
      ///////////////////	The program would  change 
    ///////////////////////////it to (98, 100, 230)

and change it.....and im trying to stay away from sync...i want to keep this as simple as possible im trying to go step by step to learn all this stuff...thanks again!
p.s...im not to worried about how slow it is at this point

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Hawkblood

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Posted: 9th Nov 2010 16:05

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Look at dbMakeMemblockFromBitmap (or something like that). Once you create the memblock, you can modify each byte to be what you want. I would read each pixil value and then swap as needed, then do a dbMakeBitmapFromMemblock (or something like that). Each pixil value will have either RGB or RGBA (3 or 4 bytes). You'll have to find that out yourself. There may be a way to get the pixil format using db functions, but I don't know what that is.

The fastest code is the code never written.

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Mireben

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Posted: 9th Nov 2010 19:47 Edited at: 9th Nov 2010 19:52

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Quote: "im not sure how to swap from the RGB red value to its blue.
"

With the dbRGBR, dbRGBG, dbRGBB commands you can get the individual colour values out of the colour variable that you read out of the bitmap. Then you can construct dbRGB from these values, reversing the colours. Then write it back into the bitmap, for example with dbDot (if it works, some computers have a problem with that) but you need to set the current bitmap to let the system know that you are drawing to bitmap and not the screen.

Another way is to use bit masking and shifting to get the colour values out of the variable. That will probably be faster and if you use memblocks, then I think that should be the preferred way, even if it takes some experimenting to get it right. In this thread you will find an exercise about manipulating colours with bit shifting, to point you in this direction (search for "colour conversion").

http://forum.thegamecreators.com/?m=forum_view&t=177106&b=22

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im not really here

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Posted: 10th Nov 2010 00:16

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ahh! i want to replace pixel using i missed that in the book...thanks....is there a simpler way to test the pixel and reverse from red value to blue? like its exact opposite ...thanks again guys

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im not really here

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Posted: 10th Nov 2010 02:20

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never mind i figured it out....woot woot!

+ Code Snippet

int width=dbScreenWidth();
  int height=dbScreenHeight();
	dbLoadImage("cow.bmp",1);
	dbCenterText(320,240," WELCOME TO COLOR SWAP!");
	dbCenterText(320,250,"Please allow a few moments for the image to change colors");
	dbCenterText(320,260,"AFTER THE IMAGE APEARS PRESS SPACE BAR TO CONTINUE");

	dbWait(6000);
	dbPasteImage(1,0,0,0);
	dbWaitKey();
	DWORD pixelColor;
	
for (int y=0;y<height;y++)   
{
	for(int x=0;x<width;x++){
pixelColor=dbPoint(x,y);
    int pRed=dbRGBR(pixelColor);
	int pGreen=dbRGBG(pixelColor);
	int pBlue=dbRGBB(pixelColor);
	DWORD reverse =dbRGB(pBlue,pGreen,pRed);

dbDot(x,y,reverse);
		



	}}}

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