Model's edges altered during rendering

Hello, I am trying to render models and capture images using the libgazebo ros camera plugin, converting the images to cv::Mat and saving them. In order to easily segment these objects with image processing, I set the background to an arbitrary color, let's say green (0, 255, 0). However, if you zoom in the attached image example, the background mixes up with the model, someway blurs it and changes the colors in the model's edges, making them greenish. Can anyone provide a way to fix this and get clean edges? Thank you, [img.bmp](/upfiles/14568595164865668.bmp)