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# URGENT- Change a buffer - URGENT

Posted on 1998-12-16
Medium Priority
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I have a buffer defined as:

buf = (unsigned long*)malloc(imageWidth*imageLength*SamplePerPixel);

Where SamplePerPixel is 4 (A,G,B,R; four components defining a pixel, the RGB components and the alpha channel)

Then, this buffer has this structure: A,G,B,R,A,G,B,R,....

Now, i want to store in a supplied buffer, called dest,  ONLY this information of the pixel: R,G,B...

Then, Dest will have this structure: G,B,R,G,B,R,G,B,R..

What must i do??
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Question by:Sol
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LVL 8

Expert Comment

ID: 1180346
I think what you want:
1. allocate a 2nd buffer if you don't have it.
2. You can calculate the size of the 2nd buffer by multiplying the orig size by 3/4 (round up as you may have partial bits)
3. Do you have 4 of A, 4 bits of G, 4 bits of B, etc.  or it is 4 bits per pixel total ?

In either case use shifts (<<) and & to rearrange the layout byte by byte.

If you explain what you mean (Item 3) then I or others can give you the exact shifts etc. required
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LVL 22

Expert Comment

ID: 1180347
How many bits in each component?  that makes a huge difference.
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LVL 84

Expert Comment

ID: 1180348
Given malloc(imageWidth*imageLength*SamplePerPixel), and  SamplePerPixel is 4,
it would imply that each component is one char.
But what do you want it to be in dest?  (unsigned long*) may not match well with malloc(imageWidth*imageLength*3)
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Author Comment

ID: 1180349
Hi!!

The buffer called buf is assumed to be an array of imagewidth times imageheight 32 bit entries, then, buf pixels are 8-bit packed red, green, blue and alpha samples.

Now, i want to store in dest ONLY 3 samples per pixel. Dest pixels must be 8-bit packed red, green, blue samples.

If dest could be allocated as: (LPBYTE)malloc(ImageWidth, ImageHeight,SamplePerpixel), it would be PERFECT!!!

(LPBYTE) means pointer to byte.

THANKS ALL!!

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LVL 22

Accepted Solution

nietod earned 280 total points
ID: 1180350
It sounds like you have these color components in a single byte and want to keep them that way, but remove the one component (alpha) is that right?  I think that is what you want but there are little things in there that don't completely mesh with that, so I'm not sure.  Assuming that is it.

unsigned char destPtr = new char [imageWidth*imageLength*3];
const int PixCnt = imageWidth*imageHeight;

unsigned char * dPtr = destPtr;
unsigned char * sPtr = ????; // your source data.
for (int i = 0; i < PixCnt; ++i)
{
sPtr++; // Skip A
*dPtr ++ = *sPtr++; // copy G
*dPtr ++ = *sPtr++; // copy B
*dPtr ++ = *sPtr++; // copy R
}
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