Sorry, but I can't replicate the problem. I have attached a sample project which works fine for me. Please change it to replicate the problem and attach to your next post.
Here is a modified version of your source. As you can see, the image in the column header does get a different size than the image original size ( 16x16 ). The original image is also shown in a small picturebox on the bottom of the application form. I expected the image to look identical to this in the column header, but it does not.
Any help is apprishiated.
Thank you for the sample project. The cause of the problem is in your code. You are creating the ImageCollection at runtime and do not adjust its ImageSize property. By default, the image size is 16X16 size. Thus your image is stretched by the ImageCollection itself. I have corrected your project so it works as expected now.