What's displayed when viewing raw image files

[ajax]

One of the nice things about XnView (MP in my case) is the ability to view (display image for) raw files (e.g., that came in lots of different proprietary formats). I've always assumed that what I'm looking at is what is called the "Preview Image". I think that is in jpg format and would be created by the camera at least in those situations where the raw file is produced by a camera. When post processing raw files, using various different software products, I like to extract said Preview Image in order to know what the camera developed image looks like. At present, I use exiftool for this purpose.

Something I have noticed is that when displaying raw files, XnViewMP displays a warning message indicating that the file is being converted to 8bit format. I've always assumed this warning was triggered because the original file contained bit depth greater than 8bits. In that, NOT because XnViewMP is actually developing an image. Yes?

My question arises because of some experiments I've undertaken recently using Adobe DNG Converter (ADC) to create Adobe Digital Negatives has resulted in some strange findings. In simple terms this amounts to observing that what is displayed by XnViewMP for such a digital negative (i.e., .dng file) is conspicuously different than what is displayed when viewing the original raw file produced by my camera. Since my expectation was that ADC was simply reformatting the original raw file I expected something as standard as an embedded .jpg file would NOT (necessarily) be altered.

At the same time, I have noticed that ADC has some options that affect the Preview Image which imply that changes are possible. However, I've now produced a set of .dng files using all of these options and none of the preview images are the same as the one in the original raw file.

Since I am relying on XnViewMP to view all of these files for judgement purposes I thought it important to correctly understand what is being displayed when selecting a raw file to include .dng format files.

[xnview]

It depends on Settings>View - Camera RAW. If you select 'embedded preview', XnView try to extract the embedded JPEG, else RAW will loaded.

[ajax]

It depends on Settings>View - Camera RAW. If you select 'embedded preview', XnView try to extract the embedded JPEG, else RAW will loaded.

Well now, I was NOT familiar with that setting. However, I noticed something quite interesting. My curiosity about this arose because of some issues that arose with my workflow when developing raw files. Briefly, I recently acquired a new camera and discovered some problems with the software I've been using to develop the raw files produced by the camera. I've been a big fan of XnView for some time now and rely on it quite heavily for viewing all sorts of images and the fact that it allows viewing of the raw file, as well, is very helpful.

Anyway, the issue regarding my new camera essentially meant the software I was using did NOT properly support the newer raw files produced by the new camera. This caused me to look toward a well known program called Adobe DNG Converter for the purpose of converting my raw files into a format supported by the development software. Right away I noticed that the converted files looked quite different (when being viewed with XnView) from that of the original raw file.

Also, I discovered that Adobe DNG Converter offers some options that pertain preview images. The choices are "None", "Full Size", and "Medium Size" which is quite similar to some of the terms used by XnView for the setting referenced as "View>Camera Raw" which include "Full Size" and "Half Size". This causes me to be interested in knowing more specifically what is meant when you say "Raw will be loaded". In that, what does that mean? If there is some reference documentation available I'd love to know about that.