Does Windows Photo Viewer on Windows 10 alter either a .jpg or RAW file in any way when opned?

I want to see the image as I took it and begin to manipulate from there. I would think RAW would be unadulterated, but using 3 RAW viewers (Windows Photos (which easily could be "helping" me without telling me), Lightroom, and Darktable and seeing 3 variations has my head spinning.

By @windsurfer65

In short, this is what determines how a raw file looks:

• In raw processing software, or on the camera, it depends on whose raw processing engine is being used, and what settings (contrast, sharpness, tone curve…) are currently in effect. Each company has its own raw processing pipeline and color science philosophy that doesn’t exactly match how other companies do it. So the same raw file can be expected to have a different default look in different raw processing software. 
• In a basic photo viewer or editor that can’t process raw files, it can only show the camera-rendered JPEG preview embedded in the raw file, and how that preview looks depends on the camera rendering engine and settings that were in effect when the preview was generated. So if it’s a Nikon raw file, it has a preview rendered by the Nikon raw engine in the camera, so it will probably not look quite like how other companies’ raw processing software would interpret the same data. You asked if the Windows software might be “helping” without telling; using the pre-rendered preview is how that’s done.

If you want more details, read on…

You’re right that a raw file is “unadulterated,” and that’s the root of the issue: A raw file has no inherent appearance. That’s because when it’s raw, it’s just a straight readout of the level of photons received at each photosite of an RGB array on the sensor. So maybe (taken from the picture below) that’s 165 from a Red photosite, 401 from a Green photosite, 228 from a Blue photosite, and 410 from a second Green photosite. (Many sensors have two green photosites in every array of RGB photosites because green contributes much more to our perception of detail than red or blue.)

That raw data must be interpreted to get to the pleasing image we expect, so somebody has to make some judgments about how that data should look. This is where you see the differences. There is no “right” rendering. It’s like if you give identical raw ingredients to six professional chefs and tell them to cook the same recipe, you will get six distinctly different dishes and maybe three of them are “perfect” but in different ways. For the same reason, if you open the same raw file in six different raw processors, how it looks depends on the differing color science opinions of each image engineering team at Nikon, Darktable, Adobe, Capture One, etc.

So if you are asking for a “true” raw image, the closest thing might be an image like the one below, as shown in RawDigger, a technical utility app for inspecting raw files. Of course the rendering looks green, because it’s showing the literal proportions of the actual recorded values, without resolving the two green photosite values into both a single green pixel value and enhanced detail. It also looks dark, because the values are being displayed as recorded (linear) and not corrected for human vision yet (by a standard gamma curve or tonal response curve). So, this is the “real” raw image “as captured in camera,” more or less. Which is different than what most people really want, which is “the image after the camera converted it from raw and rendered it, based on a certain development team’s assumptions and interpretations, altered by the user settings in the camera.”

You might notice that RawDigger also offers an RGB Render option. That looks more like the expected picture, but often not quite, because again, it’s based on a long list of assumptions, such as those shown in the picture below. The only way it’s going to look the same in all software is if every single assumption and aesthetic judgment is resolved exactly the same way by all software, right down to the code that decides how to demosaic values from a raw Bayer photosite array into a single rendered pixel’s RGB value. Hint: Everyone does not agree on the best looking way to process raw, so their raw applications produce different renderings.

How do you get a “nice looking” raw image “like I saw on the back of the camera?” If you want a Nikon raw file to look like it did on the camera, it should be processed as closely as possible to how Nikon does it, maybe by using a Nikon raw processing application like NX Studio.

Some engineering groups recognize that there is more than one “right” appearance, so they offer raw or camera profiles to affect the interpretation differently (such as Adobe Color, Adobe Landscape, Camera Matching…). Also, as in Lightroom Classic, you can choose or even define your own raw processing default profile and Develop settings preset. So if you and a friend both use Lightroom Classic, if you both customized the raw defaults to suit your personal aesthetic, you could open copies of the same unedited raw file into Lightroom Classic and its default look would be different on each of your computers…but the different default look would be appropriate starting points for each of you.

When you talk about basic software that doesn’t have its own raw processing engine, it can’t deal with unrendered files like camera raw images. For those applications, raw files often contain an embedded preview in a format like JPEG that most software can read. This is probably what you’re seeing in the photo viewer that comes with Windows. But what does that preview show you? It shows you a rendering based on the Nikon raw processing engine built into your camera, plus the in-camera settings (for color, sharpness, etc.) that were in effect at the moment the photo was taken. That is also how the camera renders the preview on the camera screen/viewfinder. So that preview is also not a “reference” or “true” rendering, but is also based on a large number of assumptions and settings that, if any of those were changed, would change how the image looks.

Is this a huge problem, that you can’t always make it look like the camera? Not for the many users who shoot raw specifically because they want enough latitude to make the image look any way they want. For them, there’s no interest in how the camera made it look, because they’re going to make it their own anyway. For those who want to shoot images that always look exactly as in camera no matter where it’s viewed, they can shoot in JPEG, find software with a Camera Matching raw profile they’re happy with, or just use the raw editing software provided by the camera maker which typically renders raw in a way that matches the camera.