The need arises occasionally to make a filter wherein the sizes are based on pixels, not percentage of the image. Currently there seems to be only one way to achieve this, that is derived from the Motion Blur component, which can be used to offset an image by one pixel.
I'll post examples of the use of this method here.
I'll try and explain the method in more detail in a later post, for it isn't one of the most intuitive methods around.
Three samples follow, each work somewhat differently, but the common denominator is that they don't scale up or down with different image sizes.
Pixel-based Offset Snippet
The Percentage control of Offset is used here.
Pixel-based Circle Snippet
White Point of Levels with a Frame here.
Pixel-based Grid Snippet
And White Point of Levels with a Profile Gradient here.
In each case the input to that control is an inverse of the pixel-size of the image i.e. 1/(Size, Pixels), or a multiple thereof, such as 100/(Size, Pixels). Because the input is in inverse proportion to the image size, it basically cancels out any changes to it. Thus, whether you apply the filter to an image of 200x200 pixels, an image of 600x600 pixels or an image of 5000x5000 pixels, the size of the pixel-based element doesn't change; the offset remains the same in the first example, the circle radius remains the same in the second, and in the last one the grid size remains the same.
In fact, from the last 100-pixel-grid image you can easily see that the FF Library preview is 512x512 pixels. (In the other examples, the grid is made with the Tiles Component which scales with the image.)
|Posted: November 27, 2008 3:53 am|
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