colored image to greyscale image using CUDA parall

问题:

I am trying to solve a problem in which i am supposed to change a colour image to a greyscale image. For this purpose i am using CUDA parallel approach.

The kerne code i am invoking on the GPU is as follows.

__global__
void rgba_to_greyscale(const uchar4* const rgbaImage,
                   unsigned char* const greyImage,
                   int numRows, int numCols)
{
    int absolute_image_position_x = blockIdx.x;  
    int absolute_image_position_y = blockIdx.y;

  if ( absolute_image_position_x >= numCols ||
   absolute_image_position_y >= numRows )
 {
     return;
 }
uchar4 rgba = rgbaImage[absolute_image_position_x + absolute_image_position_y];
float channelSum = .299f * rgba.x + .587f * rgba.y + .114f * rgba.z;
greyImage[absolute_image_position_x + absolute_image_position_y] = channelSum;

}

void your_rgba_to_greyscale(const uchar4 * const h_rgbaImage,
                            uchar4 * const d_rgbaImage,
                            unsigned char* const d_greyImage,
                            size_t numRows,
                            size_t numCols)
{
  //You must fill in the correct sizes for the blockSize and gridSize
  //currently only one block with one thread is being launched
  const dim3 blockSize(numCols/32, numCols/32 , 1);  //TODO
  const dim3 gridSize(numRows/12, numRows/12 , 1);  //TODO
  rgba_to_greyscale<<<gridSize, blockSize>>>(d_rgbaImage,
                                             d_greyImage,
                                             numRows,
                                             numCols);

  cudaDeviceSynchronize(); checkCudaErrors(cudaGetLastError());
}

i see a line of dots in the first pixel line.

error i am getting is

libdc1394 error: Failed to initialize libdc1394
Difference at pos 51 exceeds tolerance of 5
Reference: 255
GPU : 0
my input/output images Can anyone help me with this??? thanks in advance.

回答1:

Now, since I posted this question I have been continuously working on this problem
there are a couple of improvements that should be done in order to get this problem correct now I realize my initial solution was wrong .
Changes to be done:-

 1. absolute_position_x =(blockIdx.x * blockDim.x) + threadIdx.x;
 2. absolute_position_y = (blockIdx.y * blockDim.y) + threadIdx.y;

Secondly,

 1. const dim3 blockSize(24, 24, 1);
 2. const dim3 gridSize((numCols/16), (numRows/16) , 1);

In the solution we are using a grid of numCols/16 * numCols/16
and blocksize of 24 * 24

code executed in 0.040576 ms

@datenwolf : thanks for answering above!!!

回答2:

I recently joined this course and tried your solution but it don't work so, i tried my own. You are almost correct. The correct solution is this:

__global__`
void rgba_to_greyscale(const uchar4* const rgbaImage,
               unsigned char* const greyImage,
               int numRows, int numCols)
{`

int pos_x = (blockIdx.x * blockDim.x) + threadIdx.x;
int pos_y = (blockIdx.y * blockDim.y) + threadIdx.y;
if(pos_x >= numCols || pos_y >= numRows)
    return;

uchar4 rgba = rgbaImage[pos_x + pos_y * numCols];
greyImage[pos_x + pos_y * numCols] = (.299f * rgba.x + .587f * rgba.y + .114f * rgba.z); 

}

The rest is same as your code.

回答3:

Since you are not aware of the image size. It is best to choose any reasonable dimension of the two-dimensional block of threads and then check for two conditions. The first one is that the pos_x and pos_y indexes in the kernel do not exceed numRows and numCols. Secondly the grid size should be just above the total number of threads in all the blocks.

const dim3 blockSize(16, 16, 1);
const dim3 gridSize((numCols%16) ? numCols/16+1 : numCols/16,
(numRows%16) ? numRows/16+1 : numRows/16, 1);

回答4:

libdc1394 error: Failed to initialize libdc1394

I don't think that this is a CUDA problem. libdc1394 is a library used to access IEEE1394 aka FireWire aka iLink video devices (DV camcorders, Apple iSight camera). That library doesn'r properly initialize, hence you're not getting usefull results. Basically it's NINO: Nonsens In Nonsens Out.

回答5:

the calculation of absolute x & y image positions is perfect. but when u need to access that particular pixel in the coloured image , shouldn't you u use the following code??

uchar4 rgba = rgbaImage[absolute_image_position_x + (absolute_image_position_y * numCols)];

I thought so, when comparing it to a code you'd write to execute the same problem in serial code. Please let me know :)

回答6:

You still should have a problem with run time - the conversion will not give a proper result.

The lines:

1. uchar4 rgba = rgbaImage[absolute_image_position_x + absolute_image_position_y];
2. greyImage[absolute_image_position_x + absolute_image_position_y] = channelSum;

should be changed to:

1. uchar4 rgba = rgbaImage[absolute_image_position_x + absolute_image_position_y*numCols];
2. greyImage[absolute_image_position_x + absolute_image_position_y*numCols] = channelSum;

回答7:

__global__
void rgba_to_greyscale(const uchar4* const rgbaImage,
                       unsigned char* const greyImage,
                       int numRows, int numCols)
{
    int rgba_x = blockIdx.x * blockDim.x + threadIdx.x;
    int rgba_y = blockIdx.y * blockDim.y + threadIdx.y;
    int pixel_pos = rgba_x+rgba_y*numCols;

    uchar4 rgba = rgbaImage[pixel_pos];
    unsigned char gray = (unsigned char)(0.299f * rgba.x + 0.587f * rgba.y + 0.114f * rgba.z);
    greyImage[pixel_pos] = gray;
}

void your_rgba_to_greyscale(const uchar4 * const h_rgbaImage, uchar4 * const d_rgbaImage,
                            unsigned char* const d_greyImage, size_t numRows, size_t numCols)
{
    //You must fill in the correct sizes for the blockSize and gridSize
    //currently only one block with one thread is being launched
    const dim3 blockSize(24, 24, 1);  //TODO
    const dim3 gridSize( numCols/24+1, numRows/24+1, 1);  //TODO
    rgba_to_greyscale<<<gridSize, blockSize>>>(d_rgbaImage, d_greyImage, numRows, numCols);

    cudaDeviceSynchronize(); checkCudaErrors(cudaGetLastError());
}

回答8:

The libdc1394 error is not related to firewire etc in this case - it is the library that udacity is using to compare the image your program creates to the reference image. And what is is saying is that the difference between your image and the reference image has been been exceeded by a specific threshold, for that position ie. pixel.

回答9:

You are running following number of block and grids:

  const dim3 blockSize(numCols/32, numCols/32 , 1);  //TODO
  const dim3 gridSize(numRows/12, numRows/12 , 1);  //TODO

yet you are not using any threads in your kernel code!

 int absolute_image_position_x = blockIdx.x;  
 int absolute_image_position_y = blockIdx.y;

think this way, the width of an image can be divide into absolute_image_position_x parts of column and the height of an image can be divide into absolute_image_position_y parts of row. Now the box each of the cross section it creates you need to change/redraw all the pixels in terms of greyImage, parallely. Enough spoiler for an assignment :)

回答10:

same code with with ability to handle non-standard input size images

int idx=blockDim.x*blockIdx.x+threadIdx.x;
int idy=blockDim.y*blockIdx.y+threadIdx.y;

uchar4 rgbcell=rgbaImage[idx*numCols+idy];

   greyImage[idx*numCols+idy]=0.299*rgbcell.x+0.587*rgbcell.y+0.114*rgbcell.z;


  }

  void your_rgba_to_greyscale(const uchar4 * const h_rgbaImage, uchar4 * const d_rgbaImage,
                        unsigned char* const d_greyImage, size_t numRows, size_t numCols)
 {
 //You must fill in the correct sizes for the blockSize and gridSize
 //currently only one block with one thread is being launched

int totalpixels=numRows*numCols;
int factors[]={2,4,8,16,24,32};
vector<int> numbers(factors,factors+sizeof(factors)/sizeof(int));
int factor=1;

   while(!numbers.empty())
  {
 if(totalpixels%numbers.back()==0)
 {
     factor=numbers.back();
     break;
 }
   else
   {
  numbers.pop_back();
   }
 }



 const dim3 blockSize(factor, factor, 1);  //TODO
 const dim3 gridSize(numRows/factor+1, numCols/factor+1,1);  //TODO
 rgba_to_greyscale<<<gridSize, blockSize>>>(d_rgbaImage, d_greyImage,    numRows, numCols);

回答11:

1- int x =(blockIdx.x * blockDim.x) + threadIdx.x;

2- int y = (blockIdx.y * blockDim.y) + threadIdx.y;

And in grid and block size

1- const dim3 blockSize(32, 32, 1);

2- const dim3 gridSize((numCols/32+1), (numRows/32+1) , 1);

Code executed in 0.036992 ms.

回答12:

const dim3 blockSize(16, 16, 1);  //TODO
const dim3 gridSize( (numRows+15)/16, (numCols+15)/16, 1);  //TODO

int x = blockIdx.x * blockDim.x + threadIdx.x;  
int y = blockIdx.y * blockDim.y + threadIdx.y;

uchar4 rgba = rgbaImage[y*numRows + x];
float channelSum = .299f * rgba.x + .587f * rgba.y + .114f * rgba.z;
greyImage[y*numRows + x] = channelSum;