private async void btnNegative_Click(object sender, EventArgs e)
{
btnNegative.Enabled = false;
Bitmap resultImg = await Task.Run(() => Contrast.Negative(state.Image));
state.Edit(resultImg);
pictureViewer2.Image = state.Image;
await pictureViewer2.HistogramView();
await pictureViewer2.GrayBandView();
btnNegative.Enabled = true;
}
