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Filter Factory is a plug-in in Photoshop which allows the user to create custom filters. Filter Factory can be accessed through Filter>Synthetic>Filter Factory.

Filter factory has 4 main component groups: the sliders on the top right hand side of the screen which will allow us to change values once we assign them some, 3 text boxes - one for each primary colour which allows us to change its values, a preview of the effects of the filter and the buttons which allows us to save, load and compile filters.

Contents 1 An example 1.1 Convert an image to grayscale 1.2 Convert an image to sepia 1.3 Adding a slider 1.4 Setting a range for the slider

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An example

The purpose of the filter built here is to make a picture look old. This will be done by turning the picture colour into sepia and allowing the user to adjust the brightness.

[edit] Convert an image to grayscale

The first thing we have to do is to turn the picture into grayscale. This can be done by assigning the value of the primary colours to the average of their sum (r+g+b/3).

DEFAULT VALUES
r = c g = c b = c

GRAYSCALE VALUES
r = (r+g+b/3) g = (r+g+b/3) b = (r+g+b/3)

[edit] Convert an image to sepia

Now we need to put give the picture a sepia look. The colour attributes for sepia are (R,G,B,)=(43,02,02) so we need to assign those values to the corresponding colours in our filter.

SEPIA VALUES
r = ((r+g+b)/3)+43 g = ((r+g+b)/3)+02 b = ((r+g+b)/3)+02

[edit] Adding a slider

Now we have to assign a slider to the values. If we put +ctl(*) in the colour textbox, Slider number * will be assigned to the colour and in this case since we are using the addition sign the slider will increase the value as its dragged.

ADDING A SLIDER
r = (((r+g+b)/3)+43)+ctl(0) g = (((r+g+b)/3)+02)+ctl(0) b = (((r+g+b)/3)+02)+ctl(0)

[edit] Setting a range for the slider

However this formula’s highest values can completely destroy the image. Furthermore with this way the slider can only increase its assigned values and not decrease them. Therefore we must alter the highest and lowest values by adjusting the scale function. The scale function has five properties, existing value, current lowest value, current highest value, new lowest value and new highest value. What the scale allows us to do is to set up a new top and bottom range for the slider. So if the scale function is slc(c,0,255,0,120), the scale will replace the 0-255 range of the slider with a 0-120 range. The scale would still have 256 points but it will only display the new lowest and highest values.

FINAL FILTER VALUES
r = scl( ((r+g+b)/3)+ctl(0),0,255,0,120)+43 g = scl( ((r+g+b)/3)+ctl(0),0,255,0,120)+02 b = scl( ((r+g+b)/3)+ctl(0),0,255,0,120)+02

Overall Filter Factory provides you with an ability to create your own custom filters which can be a great asset if you are looking for a filter which does something specific and does not exist. However the operation of Filter Factory relies on mathematical equations rather than a GUI, which can be quite off-putting to those who are not used to applying mathematical theorem.