I guess today is a “blow your mind” Friday, because we have a guest post here by Iliah Borg, the person behind the RawDigger software that is used to analyze RAW images. I had a chance to engage in a conversation with Iliah when discussing the noise performance of the Nikon Df, where he not only proved me wrong on my assumption that the Df had exactly the same sensor as the D4 (turns out that they are similar, but not exactly the same), but also shared some incredible information about testing procedures, data analysis and other crazy, mind-boggling stuff! The learning curve with photography never ends, especially when you get into the whole sensor and image processing pipeline side of it. I must warn our readers though – the below article is very technical and is not intended for beginners! Hope you enjoy it! Nasim.
If one is shooting raw, they might be interested to know if there is any benefit in using intermediate ISO settings like ISO 125, 160, etc. There is no single answer to this question, because it depends on implementation of these intermediate ISO settings in the particular camera. Sometimes they are implemented the same way as the main ISO settings, but other times they are a result of certain manipulations, like digital multiplication.
To demonstrate how this can be determined, we will first analyze the so-called Masked Pixels (often called optically black area, or simply OB), which is a portion of the sensor that we normally do not see in our images. It is covered from light, so it can be a good indicator of the lowest possible noise of the sensor, while noise is what we analyze to learn how to use a given sensor optimally. We are taking a series of shots at varying ISO settings, from the lowest to the highest and, of course, using all intermediate ISO settings available. The subject of the shots can be anything – you can even shoot with a lens’ cap on.
Next, bring the first shot of the series into RawDigger and set RawDigger preferences to display the black frame (Display Options, Masked Pixels checkbox, checked) and not to subtract black Level (Data Processing, Subtract Black checkbox, unchecked).