Flip image

[GuckTubeYT]

So, i want to flip image, but how do i flip the image? what is the function of flip image?

Sorry if my grammar is bad

[cosinekitty]

I don't have much time right now, but the basic outline will be:

• Load the PNG image from a file into an array buffer using lodepng_load_file (C) or lodepng::load_file (C++). C++ will be easier to deal with memory because it uses vector.
• Swap pairs of pixels inside the array buffer. The array will be quadruplets of numbers (red, green, blue, alpha).
• Save the array buffer back to another PNG file using lodepng_encode_file or lodepng::encode. I hope this helps.

[GuckTubeYT]

I don't have much time right now, but the basic outline will be:

* Load the PNG image from a file into an array buffer using `lodepng_load_file` (C) or `lodepng::load_file` (C++). C++ will be easier to deal with memory because it uses `vector`.

* Swap pairs of pixels inside the array buffer. The array will be quadruplets of numbers (red, green, blue, alpha).

* Save the array buffer back to another PNG file using `lodepng_encode_file` or `lodepng::encode`.
  I hope this helps.

i still dont understand about Swap pairs of pixels inside the array buffer. The array will be quadruplets of numbers (red, green, blue, alpha). , but thanks for the answer

[nigels-com]

Can be done in place, using std::swap Iterate line-by-line from the start, and line-by-line from the last line. Swap each channel for each pixel in each line.

[GuckTubeYT]

Can be done in place, using std::swap Iterate line-by-line from the start, and line-by-line from the last line. Swap each channel for each pixel in each line.

so, it will like this? std::swap(vectorresult, vectorflip);

[GuckTubeYT]

Can be done in place, using std::swap Iterate line-by-line from the start, and line-by-line from the last line. Swap each channel for each pixel in each line.

btw, can you make the example?

[GuckTubeYT]

Please anyone help me

[AllocatedArtist]

It's a little late, but for anyone struggling with figuring out how to flip an image, you can take a look at the vertical flip function in stb_image: stbi__vertical_flip, which can be ported to your use case pretty easily. For a more C++ oriented version:

//where bytes_per_pixel is sizeof(unsigned char) * number_of_channels (usually 4)
size_t bytes_per_row = static_cast<size_t>(width) * bytes_per_pixel;

for (int row = 0; row < (h>>1); ++row) {
  auto row0 = image.begin() + row * bytes_per_row;
  auto row1 = image.begin() + (height - row - 1) * bytes_per_row;

  std::swap_ranges(row0, row0 + bytes_per_row, row1); 
}

At the moment I'm not sure if there is already a function to do this within lodepng itself, but the above solution works for me.