Plot

A powerful tool to examine sequence quality⚓

The plot can now display various information from the registration or user-requested PSF analysis. Plots of varying information from the PSF fit for each image can be done, but also data clouds to get a better idea of the distribution of star roundness and FWHM together for example.

Data used to create the plot can be exported to a comma-separated file for external analysis,

TipUse of csv data export⚓

It is very useful for observing variable stars, like Eclipsing binary of Algol type, or make statistics on the sky quality, among many other uses.

Default view⚓

After a first registration a graph is displayed

Tip

The reference image is surrounded

You can select a reference image before computing a new alignment with reference to it

Tip

Use show/hide list of images in the sequence with registration data in gray channels images windows to select or deselect images

Tip

The current image is selected by a double click in the list

Tip

The reference image is selected in the Sequence tab

Get more information⚓

You can also choose to have more information to set your reference image or remove images

ProcedureGet more information from a set of images⚓

Tip

When you use this feature for other purposes than stacking, it is more meaningful to obtain additional information about a sequence, if it has been normalized.

Tip

No registration is necessary, simply load the sequence

  1. Pick up a star

    In Gray Channels images windows

    Draw a box around the star

    Tip

    Use zoom level for more accuracy

  2. Right click and choose PSF for sequence

  3. Repeat the previous step until you have a representative sample of stars

  4. Result
Comments

Now you have the following information to optimize your choices for the selected image or the reference image:

  • Roundness

  • FWHM

  • Amplitude

  • Magnitude

  • Background

  • Star position on X axis

  • Star Position on Y axis

Tip

Each star is identified as a circle which color is identical to the color of the corresponding curve in the graph.

TipAdditional data⚓

When Siril is launched in command line from a Linux console

Additional data is displayed in the console as the position of the selection and its size in pixels

Screen

  • 1 Selected reference image⚓
    Selected reference image

    The reference image is surrounded

  • 2 Select which information⚓
    Select which information

    • Roundness

    • FWHM

    • Amplitude

    • Magnitude

    • Background

    • X position

    • Y position

  • 3 Information⚓
    Information

    Select the source of graph information.

    • Photometry

    • Alignment

  • 4 Export⚓
    Export

    Export graph to csv

    ExampleExploitation of a csv export: Cy Aqr2⚓
  • 5 Clear all⚓
    Clear all

    Reset graph data

  • 6 Clear latest⚓
    Clear latest

    Erases the last curve

    Back to screen

Advice

The model computes a Gaussian task with two axes, the major axis X and the small axis Y for the slightly elongated stars.

Roundness⚓

Note

The roundness parameter. It is expressed as fwhm_Y /fhwm_X

Warning

The range is 0 to 1

FWHM⚓

Note

The Full Width Half Maximum[1]

Amplitude⚓

The maximal intensity of the star in the [0, 1] range: it is the A parameter in 2d Gaussian[2] model.

It is the peak value of the fitted function, located at the centroid coordinates x0 and y0.

Magnitude⚓

Note

The magnitude is the integral of the Gaussian

Warning

Without Calibration with setmag It is given in ADU units[3]

Tip

You can normalize your sequence and use the command setmag to calibrate the selected star's relative magnitude

Note

setmag associates an ADU integral with an apparent magnitude value and allows to express the apparent magnitude of the other images. It is just an offset.

Background⚓

Note

The sky background is an average of the sky background pixels around the star or the level from which the gaussian starts.

Star position on X axis⚓

Warning

Do not make registration

Star position on Y axis⚓

Warning

Do not make registration

Tip

You can use these data to calculate the mount's periodic error curve with the appropriate sequence.

csv data export⚓

You can export data of an images sequence⚓

Order of columns: number of the image, sample n to n+x

NoteYou can export data for :⚓

  • Roundness

  • FWHM

  • Amplitude

  • Magnitude

  • Background

  • X Star position

  • Y Star position

Tip

The csv file is saved by default in the current working directory

Tip

Use Stellarium or Kstars in association with astrometry.net remotely or locally to identify the stars

Setmagseq⚓

Conceptsetmagseq⚓

setmagseq magnitude

This command is only valid after having run seqpsf or its graphical counterpart (select the area around a star and launch the psf analysis for the sequence, it will appear in the graphs).

This command has the same goal as setmag but recomputes the reference magnitude for each image of the sequence where the reference star has been found.

Tip

When running the command, the last star that has been analyzed will be considered as the reference star.

Displaying the magnitude plot before typing the command makes it easy to understand.

Note

To reset the reference star and magnitude offset, see unsetmagseq.

ExampleExample of using the Setmagseq command⚓

Make a usual seqpsf to have a curve.

  • Display the graph of magnitudes to have a visual feedback

  • Type setmagseq 10 if it does 10 of magnitude

  • Take a look to the result

Note

The last star that was studied with seqpsf is defined as reference.

Tip

Look at the info messages on the console output tab

Tip

Undo with unsetmagseq