CCD/CMOS Mode

 

This is how Histogram Aid looks like when APT is in CCD/CMOS mode. Usually the CCD/CMOS sensors have from 12 to 16bits dynamic range which is hard to be displayed on screen especially when we talk about combination of weak object and brights stars. Because of that there is need to make a signal compression and/or signal boost (stretching) in order to see more details from the raw data. The Histogram Aid allows to combine both compression and stretching in order to see most of the faint data without using processing application. The stretching is implemented by two types - by placing black and white points manually or automatic (by calculating good black/white points) or with fully automatic stretching like "Screen Transfer Function" in PixInsight which is analyzing the image for showing most of the weak signal.

 

In short when Auto is enabled there are four options for automatic stretching:

 

See below for details how to use Histogram Aid in more details.

 

When you are working with black/white points, there is possibility to apply histogram compression using Local mode. When this mode is enabled APT makes one automatic compression by determining the lowest and highest tones in the current image and to work with this limited Range allowing mode detailed stretching. This is similar to defining additional black/white points that bounds the recorded signal and excluding the left and right areas without data.

 

In the sample below the Range is from 2000 to 65520 which means that there is no pixels with ADU less than 2000 and bigger than 65520, so there are set hidden black/white points at these borders. Also very left point of the graph shows the tine 2000, the very right shows 65520.

 

 

 

Enabling Local mode works well for bright frames (light, flats, framing), but sometimes lead to different screen representation of "similar" to dark and bias (sometimes flat) frames where the Range is very small. Random hot pixels can change the Range and as result two bias frames can have different brightness on the screen. There are no problems because the stored data is fine and this is only screen representation. Sometimes the automatic stretching works better with enabled Local mode, in other situations stretching on whole range gives better preview. It depends on how faint the object is, exposure, sky conditions and etc.

 

Follows detailed description of the Histogram features.

The image stretching is invaluable option when we are working with weak signal (which is 99.9% of the time), saving the time to transfer the image to an image processing application just to see where and if the object is in the Field Of  View - FOV.

 

Here is a sample of un-stretched image. As you see, only few stars are visible.