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CCD/CMOS Mode

 
This is how Histogram Aid looks like when APT is in CCD/CMOS mode. Usually the CCD/CMOS sensors have 16bits dynamic range which is hard to be displayed on screen. Because of that there is need to make a signal compression and boost (stretching) in order to see more details from the raw data. APT makes one automatic compression by determining the lowest and highest tones on every image and working with this Range. This is similar to defining 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 914  to 47786 which means that there is no pixels with ADU less than 914 and bigger than 47786, so there are set hidden black/white points at these borders. Also very left point of the graph shows the tine 914, the very right shows 47786.
 
This approach works well for bright frames (light, flats, framing), but sometimes lead to different screen representation of "similar" dark and bias (sometimes flat) frames. 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.
 
CCD/CMOS Mode
 
The screen below shows how defined black/white point looks like. The dark area is the range between the black and the white point that will be used for manual or automatic screen stretching. When Auto Stretching is disabled you can set the point manually using the following combinations. Shift+Double Left click set the black point. Shift+Double Right click clears the black point. Double Left click set the white point. Double Right click clears the white point. Below are described and other way to move the points.
 
 
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.
 
 
 
This is the same image after applying the "Auto-Str R". The M78 nebula becomes obvious and it is easier to evaluate the image.
 
 
 
 
1

Auto-Str Left

1. Auto-Str Left
 
Enables/Disables the "Left" automatic stretching. This methods works with the most left peak in the histogram and gives better results when there are many saturated areas in the image.
 
2

Auto-Str Right

2. Auto-Str Right
 
Enables/Disables the "Right" automatic stretching. This methods works better when there are several signal peaks that you want to use or just one peak and when there are no many saturated areas.
 
 
3

Clear

3. Clear
 
Disables "Auto-Str L", "Auto-Str R" and clears the set black and white points
 
4

Range

4. Range
 
Shows the image signal range.  The weakest and strongest tones stored in the current image.
 
5

Log

5. Log
 
When is active (high-lighted) it shows the logarithmic representation of the data.
 
6

Show/Hide

6. Show/Hide
 
Show/Hides the section for "by step" black/white points moving.
 
7

Black Point

7. Black Point
 
Moves the black point in left or right with the selected step (Coarse/Fine)
 
8

Coarse/Fine

8. Coarse/Fine
 
Switches between the Coarse and Fine fine step modes.
 
9

White Point

9. White Point
 
Moves the white point in left or right with the selected step (Coarse/Fine)