Why does my Lightroom/Photoshop preview change after loading?

This often depends on how you originally import. Most RAW files include a JPEG preview image embedded in them. You have a variety of thumbnail options when importing, including 'Embedded & Sidecar'. The JPEG preview will often look different than the unprocessed RAW file, and when using 'Embedded' thumbnail processing, the embedded JPEG thumbnail will be used as the initial thumbnail image. When you select an image, a true preview is regenerated from the RAW data, and that will usually look different as it is unprocessed data.

There is also the 'Standard' thumbnail generation option (as well as 'Full'), which will basically use the embedded or sidecar thumbnail first, then as part of the import process, automatically generate new thumbnails based on the RAW data. You will see your thumbnails change as the import process progresses, as thumbnail generation is slightly lazy compared to the initial import.

The difference should be expected in most cases. Camera JPEG generation usually applies some processing based on a selected tone curve, and obviously does some compression. Between the processing and the lossy compression, the appearance of JPEG thumbnails will generally look different than unprocessed RAW images. Nikon cameras may be "more affected" by this simply because of the kind of processing and tone curves they apply to their JPEG thumbnails. Technically speaking, a JPEG is not an accurate representation of what your camera actually captured....where as RAW would be.

Even Adobe mentions that their import options allow previews to be generated based on "the smallest previews embedded in the photos". This is the JPEG image you see on the back of your camera. Connor is correct. There is a lot more information in a RAW/NEF image than just sensor data. The preview JPEG is just one of them.

To the OP's problem though, you can prevent this by selecting the "standard" option on the render previews pull-down. The trade-off is your import time will increase.

The image in the preview comes from an embedded JPEG inside the raw file which was generated by the camera, while the image you see when you open the raw file in Lightroom is generated by Lightroom based on the raw data itself.

The raw image data is captured from the camera at a point before the contrast and color settings are applied by the camera, so any difference in appearance will be from differences in the way the camera, and Lightroom, decided to render the color and contrast.

Every manufacturer's cameras come with embedded color profiles and contrast curves which dictate how colors and contrast should look when transferring from the raw image data into a full color image, as is done when the camera generates its own JPEG image or the embedded JPEG inside a raw file. These color profiles have subtle differences between manufacturers, for example some of them emphasising skin tones or blue colors, and others taking a more "natural" approach vs wanting their own characteristic "look". Even the "normal" contrast setting can vary between camera manufacturers.

When using third-party raw editors to generate an image from the same raw data, that third-party raw editor probably won't use exactly the same color profile and contrast curve as your camera. It also won't necessarily honor the same contrast curve (or contrast setting) that you selected in-camera. Thus, the image will look different: brighter, darker, less or more contrasty.

If you use raw editing software by the same manufacturer as your camera, you may be able to use the same color and contrast settings that are baked into your camera, ensuring a good result. However, just because something looks "the same as in camera" doesn't mean it looks better - ultimately, a raw editor will give you greater control over color and contrast than your camera's built-in settings will, resulting in greater scope to modify the final product.

The main reason Lightroom's generated preview is so different from the embedded one is because it's generating the preview with the Adobe Standard camera calibration by default, whereas the embedded one was generated using the Picture Control setting you have in the camera.

To make Lightroom's previews closer to Nikon's, what you can do is:

1. Create a Lightroom development preset whose only contents are having the Camera Calibration setting set to the camera's Standard, or Neutral, or whatever Picture Control setting you use in the camera.
2. Have Lightroom apply that preset to every photo as it imports it. There is a setting in the Import window to do this.

Also, if you have your camera set to apply automatic vignetting control and/or distortion control, you can include these Lens Correction settings in the Lightroom preset to make the previews match the embedded ones even closer.