CCD/CMOS Mode

 

This is how Histogram Aid looks like when APT is in CCD/CMOS mode. Usually the CCD/CMOS sensors have 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 with placing black and white points which. This can be made manually and automatically (see below). Also 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 3328 to 65532 which means that there is no pixels with ADU less than 3328 and bigger than 65532, so there are set hidden black/white points at these borders. Also very left point of the graph shows the tine 3328, the very right shows 65532.

 

 

 

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.

Powerful feature is the "Auto Stretching".  It makes automatic selection of the optimal black and white points in order to show the faint signal. In CCD/CMOS mode there are two options for automatic stretching - Left and Right. The left one works with the most left peak in the histogram and gives better results when there are many saturated areas in the image. The right one works better when there are several signal peaks that you wan to use or just one peak and when there are no many saturated areas. You can easily change between the two modes with the "Auto-Str L" and "Auto-Str R" buttons to see which one you like more for the current image.

 

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