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Overview

Blink Comparator version 1.1.0 Build 1

Blink Comparator is a tool used for astronomical analysis. Before the advent of computers, Blink Comparators were mechanical and usually supported two images. The basic idea is to observe changes in each image. This process resulted in the discovery of Pluto.

Because of the capabilities of computers though, the functions of Blink Comparator can do a lot more. Now it is possible to analyse as many images that you can load into memory. It is also possible to align each image to make the processed animation more smooth.

There are several example sets included, and a tutorial as well.


Start here

Start here

The first thing you need to do is capture some images that you want to view and maybe align and export to disk. If you haven't got any images to test, we have some prepared for you.

First go to the 'Start menu', 'Programs', 'Trefach Astronomy Centre' and 'Blink Comparator' and click on the 'Comet Neat Test' shortcut. This will load the example data. If you check the msecs checkbox on the bottom left of the window and enter 100 into the box to the right of it and click on the '>>' double chevron button, you will see the animation and as you may notice, the images are not aligned so that the animation is smooth.

So... to the next page.


Alignment modes

Alignment modes

There are three alignment modes that you can use to align your images: Manual, Auto or both.

In manual mode you align the images yourself, whereas in auto mode you simply click on the area of the first image that you wish to use as the search pattern and Blink will attempt to align all the loaded images.

You need to specify the radius of the search area. The radius is the amount of pixels from the centre of the search pattern area that define the scope of the search. The auto search is pretty slow because it involves a lot of processing even for a fast machine and the greater the radius the slower the search will take.

However, if you choose manual and auto then you move the search box over the search area for each image which will help blink to align the image. You don't have to position the search box or cursor exactly as you did before, but a combination of a small radius and good positioning of the search cursor will speed things up.

As computers get faster however the auto function will probably work fine on it's own.

So... to the next page.


Choosing a cursor

Choosing a cursor to use to align images

There are two types of cursors used for slightly different situations. The set of images you see now are of a comet making it's way across the sky. In this case all we need to do is choose one of the stars in the background and use that star as an alignment point. So we use the cross hair cursor. Which is the 8th icon from the left, or the Toggle point/extended cursor option in the Align menu. You toggle this button until the red 'cross hair' cursor is visible.

The frame [extended] cursor is used for a situation, for example, when you are aligning a image of Venus transiting the Sun. The 'Venus Transit (extended)' shortcut demonstrates that the Sun is stationary and Venus is moving across. If you were to use the Cross hair cursor and use Venus as the alignment point then the 'Venus Transit (point)' demonstrates that this approach might not be ideal.

Now we need to align the Comet Neat images...


Aligning with the point cursor

Selecting the alignment points for each image

Ok, first we assume you are doing a manual or manual/auto align by making sure that the manual or manual and auto buttons are depressed. We decide on a star to use as your reference point. When you have decided, click on the Chain alignment process button, or click on Select alignment points from the Align Menu.

Move the cross hair cursor so that your reference point is centered in the middle of the cursor and click on the left mouse button. At this point if only the auto button is depressed then alignment will continue automatically. Also note this might take a long time depending on the radius you have specified. Otherwise the next image will be displayed, so carry on selecting the alignment point until all frames have been selected.

If you are aligning automatically then the align function will be triggered automatically otherwise, you need to click on the Align images button or select the Align images option in the Align Menu.

Once you have done this, click on the '>>' double chevron button to start the animation.

Now you have succesfully aligned a set of images. To save the alignment information for each image click on the Save alignment configuration button or select Save alignment file in the File Menu.

So, how do you use the frame cursor...


Extended Cursor example

Extended Cursos example

Now select the 'Venus Transit Test' shortcut in the Blink Comparator start menu folder and click on the '>>' animate button. As you can see, the images are roughly already aligned, but there is room for improvement. Because we dont have any stars for alignment points we just have the Sun or Venus. But if we use Venus with the point cursor then it will be the Sun that will move, so we need to use a different type of cursor.

Click on the Cursor type button until it changes to a dotted square. You will notice that the button next to it also changes to a dotted square with a tick. Both of these buttons work together, first you click on the Chain alignment process button and you will notice that a dotted rectangle will appear in the middle of the image.

You move the cursor over each edge and click once, you don't need to hold down the mouse button when you move the edge of the frame. Simply move the edge until it is on the edge of the Sun and click once again. This will set the posistion of that edge of the frame, you can do this with all sides as many times as you like until the frame fits the alignment object as you want.

Once you are happy with the frame cursor, click on the accept frame button or select the 'Accept frame' option in the Align Menu.

Then as with the point cursor it is a case of selecting an alignment point for each frame unless you only have the auto button depressed in which case alignment will continue automatically. Also note this might take a long time depending on the radius you have specified and the size of the search box. Otherwise in this case, you can use the cursor keys to fine tune the position of the cursor and press the enter key when you want to set the alignment point.

Then when you have set the alignment point for each image and the auto button isn't depressed, click on the Align button or select the 'Align images' option in the Align Menu.

Now you can save your alignment information.

And export your images.


Open Images

Open Images

Click on this button, or select Open Images from the File Menu to read images into the editor. To save time, always make sure that the first image in the list is selected last. This is a Windows thing and it saves having to move the last image to the start of the list.

Once loaded, each image is listed in the Image List Box. You can select one or more images and move them if they are not in the right order.

Once the images are in the right order, you can use the Slide Show feature to rotate through the images in the list changing the time to delay each image.

If the images are jerky and not aligned, then you need to Align each image


Open Alignment File

Open Origin Alignment File

Click on this button, or select Open Alignment File from the File Menu to read a set of images with the pre-configured Alignment Information into the editor.

Once loaded, all the images and the aligmnent information for each image previously recorded in another session are also loaded.


Save Alignment File

Save Origin Alignment File

Click on this button, or select Save Alignment File from the File Menu to save a information file containing the location of the images currently open and any Alignment information to the selected storage device.

Once saved, all the images and the aligmnent information for each image recorded can be re-loaded.

When you save a Alignment File the images are not actually modified. In order to save the images like they appear once aligned you can Export the images as they appear after they have been aligned.


Export Cropped Images

Export Cropped Images

Click on this button, or select Export cropped images from the File Menu to save each image that has been aligned and cropped. The images are saved all the same size and are given filenames based on the name you supply in the dialog box.

Once saved, all the images can be combined into a GIF editor of which there are many, and some are freeware.


Delete Selected Images

Delete Selected Images

Click on this button, or select Delete selected from the Edit Menu to delete each image that is selected in the Image List Box The images are deleted from the list box, but are not actually deleted from the same storage device that they were read from.


Chain Alignment Process

Chain Alignment Process

Click on this button, or select Select alignment points from the Align Menu to start a process that repeats until all images in the Image List Box have been marked.

You mark the alignment point in each image in one of two ways. To align on a small object, like a star you choose the Cross Hair Cursor and centre it on the object. However this may not be desirable when the small object is the one that is moving, so you may need to use the Frame Cursor and position it over a large object like the Sun or Moon.

Before you start aligning each image with the Frame Curosr you need to drag each side of the frame so that the frame fits the target object.

Once each image has been marked, then you click on the Align Button to finish the process.


Accept Frame Cursor shape

Accept Frame Cursor

Click on this button, or select Accept frame from the Align Menu to accept the shape of the Frame Cursor.

Once this has been done, you start the Chain Alignment process.

This option only works when the Frame Cursor type is selected with the Cursor Type function.


Select Cursor Type

Select Cursor Type

Click on this button, or select Toggle point/extended Cursor from the Align Menu to change the cursor type.

If the cursor type is a Frame Cursor type, then before starting the Chain Alignment process you need to modify the frame so that it fits the dimensions of the large object you are aligning each image on.

Once this has been done, you start the Chain Alignment process.

If the cursor type is a Cross Hair type then you can then simply start the Chain Alignment process and centre the cursor over the small object you are aligning each image on.


Align Marked Images

Align Marked Images

Click on this button, or select Align images from the Align Menu to complete the Alignment Process.

This is the last process in aligning images.

Once aligned, the images can be shown in a Slide show using the Play control panel.


Move Image in list Up

Move selected images up

Click on this button, or select Move image up from the Edit Menu to move the selected images in the Image List Box up one place.

If any of the selected images are already at the start of the list then their position will remain unchanged.


Move image in list Down

Move selected images down

Click on this button, or select Move image down from the Edit Menu to move the selected images in the Image List Box down one place.

If any of the selected images are already at the end of the list then their position will remain unchanged.


Image List Box

Image List Box

This is where the Images that have been loaded from a storage device either by Opening Images or indirectly by loading a  Alignment File which will reload any images that were recorded in the file when it was Saved.

You can select images and move or delete the images.

Once images are in the desired order then you can Align the images.


Select Milliseconds

Select Milliseconds

Check this box if you want the value in the Interval edit box to be interpreted as milliseconds.

If this box is unchecked then the value will be interpreted as seconds.


Animation Interval

Animation Interval

Enter the value that you wish the interval for the image animation.

If the Milliseconds check box is checked then the interval will be interpreted as milliseconds. Otherwise value will be interpreted as seconds.


Animation Control Panel

Animation Control Panel

'<<' Animate backwards.
'<' Single step backwards.
'stop' stop animation.
'>' Single step forwards.
'>>' Animate forwards.
'hide' Hide all controls.

When hide is enabled, a single click on the window will restore the controls.


File Menu

File Menu

Open Images
Open Alignment File
Export cropped images
Save Alignment File
Exit Close Blink Comparator.


Edit Menu

Edit Menu

Delete selected images
Move image up
Move image down


Align Menu

Align Menu

Select alignment points
Toggle point/extended Cursor
Accept frame
Align images


Help Menu

Help Menu

About The about box which displays the splash screen.
Help Display this file.