# Modifier-Based Zoom

You can change a layer’s zoom setting using a modifier. Why you would want to do change a layer’s zoom is subject to what you’re trying to do. One example might be that you are going to use an effect you created as part of a style. That style contains a rotation center change. Because of the way rotation center changes work, if a change is made to a layer’s size, aspect, or position, the rotation center changes. If you know how to do it, you can set up the style to recognize a zoom change for the primary image and have all of the secondary images change their size automatically and accordingly. A size change in this case might be necessitated by the fact that the main image size change was required to make it fit completely within a mask. If there are any smaller versions of the same image (which may be visible now or later as the slide is played), you can change them to fit their masks as well (and any associated rotation center changes) without having to manually change the settings for each layer.

The possibilities are limited by your imagination.

A modifier changes the existing zoom value by a percent that zoom. So, if the layer has a zoom value of 30, a constant modifier of 1 changes that zoom value by 1%. If the constant modifier is 20, the zoom value is changed by 20%. If you’re trying to increase a number by a certain percent then you’d use the first equation:

ZoomStart + ZoomStart(%ChangeModifier/100) = ZoomEnd, (eqn 1)
Where “%ChangeModifier” is a decimal number. ZoomStart is the layer’s initial zoom value. ZoomEnd is the zoom that you want the layer to end up at.

With this equation, you can check out what modifier values give you what final zoom when given a starting zoom. It’s helpful to realize that the modifier value is actually a number that represents a percent. That is, a modifier of 125 represents 125% which is actually a decimal value of 12.5. A modifier of 1 is 1% which is actually a decimal 0.01.

If you’re looking for the modifier value that you would get with a given start and end zoom, you’d use the following formula:

%ChangeModifier = (ZoomEnd – ZoomStart)100/ZoomStart (Eqn 2)

The reason I added the “100” value into the formulae is so that the final result would be the actual modifier value that you would use in your modifier action (remember, a modifier value is not just a number, its a Percent value). If you forget to convert the decimal number to the percent number and use that decimal value instead, you will NOT get what you expect (yes, it’s easy to do!). Hence, the inclusion of the 100 into the formula. This is particularly important if you put the actual formula in the modifier actions: +ZoomEnd – ZoomStart * 100 / ZoomStart (and yes, there are times when you may want to have the program calculate the values for you on the fly …)

If you wanted to, for example, create a thin border around your image you would want to increase the size of a single color gradient or solid color layer by a small amount and place it behind your image. In this case, assume our starting zoom is 65. If we only want a 0.5% increase our thin border calculation would be:

%Changemodifier = (65.5 – 65)100/65 = 0.7692, or 0.77 (modifiers only round to 2 decimal places).

If you wanted a thicker border of something like 5%, then we’d have

%Changemodifier = (70 – 65)100/65 = 7.692, or 7.69

UPDATE 111114

When the layer’s zoom remains constant throughout the slide time, a constant value zoom box modifier changes the existing zoom value by the percent represented by the modifier. So, if the zoom is 100 and the modifier value is 20, the layer’s zoom is increased 20% to 120. That is, starting zoom is 100 and the ending zoom is 120, a difference of 20. That’s because 100 * 20/100 is 20. Or, if the starting zoom is 65 and the modifier is 60, the increase in zoom is calculated as follows: 65 * 60/100=39 (the difference between starting and ending zoom). So, the final zoom value is 65+39=104.

Things change a little when it comes to a slidetime that has varying zoom values. If a constant modifier is entered into the zoom box it effectively creates a difference value between the slide time’s largest zoom value and the percent of that value calculated by the modifier value. So, if the slide’s largest zoom value is 60 and a constant zoom modifier value of 75 is added, the ending modifier-adjusted zoom is now 105 and is calculated as follows: 60 + 60(0.75) = 60 + 45 = 105. The difference between 105 and 60 is 45. All other zoom values in the slide time are now increased by 45 as well. if there’s a zoom of 20 in the slide’s timeline, its new zoom value is 20+45=65. If there’s a zoom of 40, it’s zoom becomes 85.