What are the basic low level steps involved in raw file conversion? In this article I will discuss what happens under the hood of digital camera raw converters in order to turn raw file data into a viewable image, a process sometimes referred to as ‘rendering’. We will use the following raw capture by a Nikon D610 to show how image information is transformed at every step along the way:
You have obtained a raw file containing the image of a slanted edge captured with good technique. How do you get the Modulation Transfer Function of the camera and lens combination that took it? Download and feast your eyes on open source MTF Mapper version 0.4.16 by Frans van den Bergh.
[Edit 2023: MTF Mapper has kept improving over the years, making it in my opinion the most accurate slanted edge measuring tool available today, used in applications that range from photography to machine vision to the Mars Rover. Did I mention that it is open source?
It now sports a Graphical User Interface which can load raw files and allow the arbitrary selection of individual edges by simply pointing and clicking, making this post largely redundant. The procedure outlined below will still work but there are easier ways to accomplish the same task today: just “File/Open single edge image” raw files from the GUI after having inserted “–bayer green” in the additional string field. Thanks Frans.]
The first thing we are going to do is crop the edges and package them into a TIFF file format so that MTF Mapper has an easier time reading them. Let’s use as an example a Nikon D810+85mm:1.8G ISO 64 studio raw capture by DPReview so that you can follow along if you wish. Continue reading How to Get MTF Performance Curves for Your Camera and Lens