This tool is to control the aspect of the preview image. None of this setting 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.

On the left part is the histogram display with the two vertical line that indicate the current truncation level.
This lines can be moved using the red/green button at the bottom. They can be moved directly with the mouse or by a click in the bar. The position of the histogram below the mouse cursor is show at the bottom of the screen.
The color of the bar remind that only the part in the gray section is show in the image, below truncation it is black, and white above.

The default truncation level for a new image is selected in the dropdown list on the right.

• Data range preserve the highlight and is good for well exposed images.
• Low cut a part of the highlight, this is useful when this is only hot pixels.
• Medium, High and Very High can be used for DSO images.
• Extreme is to show the faintest details above the sky background.
• Manual do not modify the current truncation level when a new image is loaded.

Right of this is the Gamma value that control the stretching between the truncation levels. A value of 1.0 is linear, values between 0.3 and 0.5 are a good stretch for DSO.

On the last row are the exact minimum and maximum truncation level, the value can be modified here.

At the bottom right is the button to detach this box to a separate window. It can be resized for a more precise use of the histogram display.

On the top-right part are the geometric adjustment button. 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.

Next are two buttons to mirror the image horizontally and vertically,

On the second row the button is to limit the histogram display to available data or to show the full range 0-65535 for a quick estimate of exposure margin (not active with floating point images).
The button redraw the histogram zoomed to the current range, very useful for fine adjustment near sky background.

The button show a negative image that can help to see faint details.
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.

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.