This tool is to control the aspect of the preview image. None of the setting here have any influence to the image saved as a FITS file. They are only to help you to view the most of detail on the single raw images.

It is separated in two part, an histogram of the image and the control buttons.

On the top, a cursor control the range of histogram drawing, using 90% to 100% or the active histogram range. Reducing the histogram range make the image lighter and help to see the faint nebulae in the image.

On the histogram you can move the high (green) and low (red) clipping bar with the mouse.
You can also directly edit the low and high threshold by moving the mouse cursor to the top left or right to display the edit box.

Bellow the cursor, the numeric value let you adjust the Gamma for the display. This also help to better see the faint part of the image but without saturation of the bright area. A value of 0.45 in this box allow to convert a linear image to a display image with a standard gamma of 2.2.

The next button switch the histogram view between full range and active range.
The button show a negative image that can help to see faint details.

On the next row, the four button are preselected zoom level for the image.
You can also get other zoom level using the mouse wheel rotation
When the zoomed image is bigger than the screen you can move it with the left mouse button.

On the bottom row you can mirror the image horizontally and vertically,

The bull eye button show the mark on the image.

It is also possible to temporarily show a large cross at the cursor position by pressing the Alt or Meta key at the same time as the left mouse button.

If the image is plate solved it also display an arrow with the North and East direction and print the image rotation angle.
A focus star can be automatically selected in the square that circumscribe the external circle.

Finally the button let you check for saturation in the image.

The overflow in the highlight area is marked in pink.
The clipped shadows area is marked in yellow.
You can define the clipping level for your camera in ADU in the preferences, the default are 0 and 65535.

When using the option to not display the images during a capture, a new button appear on the right, allowing to temporarily show the captured images.