How to downsample an image with the GPU ?

[YacinoBen]

Hello,
I'm trying to downsample a Halide buffer on GPU and getting visual artefacts. The output image is unrecognizable.

I have this function

std::unique_ptr<ImageRegion>
GPU_Halide::downsample(size_t target_width, size_t  target_height) // target downsample size

I need to return the following data :

auto region = std::make_unique<ImageRegion>(
            std::move(result_data), // vector of float
            static_cast<int>(target_width),
            static_cast<int>(target_height),
            static_cast<int>(m_channels)
            );
return region;

And i have

Halide::Buffer<float> m_halide_buffer; // Already contains the full image data

How can I downsample the image with the corresponding size target? because I got artefacts and I don't know how to use a right downsample