CIS Twin

CIS-TWIN Stitches together the two images from a Twin Array file into a single image, with the ability to move the splice point about anywhere within the overlap region. Possible uses include finding the optimum Changeover and Vertical Separation settings for the CIS header and, by placing the splice down the middle of a track, observing the effects of roll weave on the registration between the two arrays.

Download

Current version 1.00, 21 June 2006. CIS-TWIN.ZIP

Instructions

CIS-TWIN works directly with Stepper scanner format Twin Array CIS files. Encoder clocked files should first be format converted with CIS-RECLOCK.

Load the Twin Array CIS file into CIS-TWIN. The program will calculate a default split point and vertical separation based on the settings in the header. If these are acceptable, or the correct settings are already known, it should be possible to skip over much of the following. Otherwise ...

Load the CIS file into the Viewer
Find a readily identifiable hole somewhere towards the centre of the overlap region and pick a point on it like, say, bottom centre
Left click with the mouse over each reference point in turn and note down both sets of coordinates

	X Coordinate	Y Coordinate
Left Array	2459	18463
Right Array	2497	18560

Enter the Left and Right Array X Coordinates into the Left Array and Right Array edit boxes
Enter the difference between the two Y Coordinates (18560-18463=97) into the Vertical Separation edit box
If the Right Array Y Coordinate is less than the Left Array Y Coordinate, check the Right Array Leading check box

If the roll margins are excessive, enter suitable values into Left Trim and Right Trim edit boxes

Determining Left Trim and Right Trim X coordinates

If Treble and Bass are reversed, as with Welte T-100 scans, check the Mirror Image box to reverse the image
Press the Save button to create the output CIS file
Keep the Twin Array file open in CIS-TWIN so that, if necessary, the settings can be fine tuned and the output CIS file rebuilt
Review the resulting file in the Viewer and check that the registration holds good throughout the file. Close the Viewer before attempting to rebuild the CIS file otherwise it is liable to be locked
The splice point can be offset sideways without disturbing the registration by making equal and opposite adjustments to the Left Array and Right Array entries
To process further CIS files using the same settings, check the Hold Settings box to retain the existing settings when another CIS file is dropped into the window

Final result

CIS Header Offsets

Having arrived experimentally at the settings producing the best registration, it's possible to derive from them the optimum Changeover and Vertical Separation settings for the CIS header.

Vertical Separation

Vertical Separation in defined in the CIS header in thousandths of an inch, as this holds true regardless of the vertical scan resolution. To calculate this figure, multiply the Vertical Separation in scan lines by 1000 and divide by the Vertical Resolution in Lines Per Inch. In the above example 97*1000/204=475 thou (always assuming that the vertical resolution is correct), which differs slightly from the figure of 490 stored in the header.

Changeover

There appear to be two definitions of the Changeover in use; take your pick.

1. The classic definition equates the Changeover to the number of pixels from each array that contribute to the final image, with the resulting image width being twice the Changeover value. The overall width must inevitably be an even number, so the horizontal registration between the two arrays can only be adjusted in 2 pixel increments. Defined in this form, the Changeover will always be more than half the array width. To calculate the Changeover value, divide the sum of the Left Array and Right Array contributions found above by two to give an average. In the above example (2459+2497)/2=2478.

2. The alternative definition equates the Changeover to the Overlap between the two arrays, with the resulting image width being twice the Array Width minus the Overlap. This has the advantage of allowing the registration between the arrays to be adjusted in single pixel increments. Hopefully the Overlap will always be less than half the array width, allowing it to be distinguished from the classic definition. To calculate the Overlap value, multiply the Array Width by two and subtract the sum of the Left Array and Right Array contributions found above. In the above example 2600*2-(2459+2497)=244, which tallies with the setting already found in the header.