I have decided on a portfolio item image size of 609 x 406 px. I have found that there is quite a noticeable degradation in image quality when WP makes its thumbnail downsizing, so I thought that if i upload the image in 609 x 406 px I will not have the degradation. (The plan is to also upload a bigger size that will be opened in lightbox.)
The problem for me now is, that even if I upload the exact size that is needed for the portfolio (609x406) the image is still being transformed into an image of the same size, but of worse quality.
If you go to http://www.thevelvetroom.dk/portfolio-item/franny-test2/ the difference should be ease to see. The image you see in the portfolio is 609x406 and has been degraded by WP. When you click on it, the lightbox opens and you will see the original, that is also 609x406. The original is noticeably sharper, and has a slightly better dynamic range.
So my question is: How can I force the portfolio item to use the original 609x406 file and NOT the 609x406 thumbnail?