The Resize tool is found on the Retouch menu of your Nikon D7100. Your resized images are saved in the JPEG format, which is the web-friendly format. To create a small copy of just one image, take these steps:
Press the Playback button to set your camera to playback mode.
Display the picture in single-image view. If the monitor currently displays multiple thumbnails, just press OK to switch to single-image view.
Press the i button to display the Retouch menu over your image.
The Resize feature creates a low-res, e-mail–friendly copy of a photo.
Highlight Resize and then press OK or press the Multi Selector right.
You see the screen shown on the right in the figure.
If two memory cards are installed, highlight the card where you want to store the small copy. Press the Multi Selector right.
The screen shown appears, offering the list of size options (stated in pixels) available for your small copy. The second value stated for each option is the megapixel count — total pixels, with one megapixel equal to 1 million pixels.
Highlight the size you want to use for your copy.
Press the Multi Selector right to display a confirmation screen.
Highlight Yes and then press OK.
The camera duplicates the selected image and downsamples (eliminates pixels from) the copy to achieve the size you specify.
When you view your small-size copies on the camera monitor, they appear with a Retouch icon at the top of the screen and a Resize icon at the bottom.