Photoshop's Smart Filters
One of the most important concepts to keep in mind when working with Photoshop's filters is Smart Filters. When you apply a filter to a pixel layer, that's it — the pixels are changed. But, when you apply a filter to a Smart Object, you create a Smart Filter.
With Smart Filters, you can apply one or more filters to a Smart Object and later change your mind about what settings — or even what filters — to use, without reverting to a saved copy of the file or using the History panel. Unlike adjustment layers, which are, in fact, separate layers in the image, Smart Filters work more like layer styles.
They appear in the Layers panel below the layer to which they're applied and can be shown or hidden by clicking an eyeball icon. (See this figure.) And, like layer styles, you can reopen a Smart Filter by double-clicking it in the Layers panel.
As you can see in the figure, the layer Inside Passage-02 (the active layer, highlighted in the Layers panel) has both layer effects and Smart Filters applied. The type layer above has only layer effects, whereas the other two Smart Objects, below in the Layers panel, have Smart Filters but no layer effects.
Clicking the triangle to the far right of a layer name expands and collapses the list of effects and filters applied. Clicking the eyeball icon to the left of an item hides it without removing it.
You can delete a Smart Filter by dragging it to the Trash icon (just as you can with layer effects), which removes its effect from the Smart Object. To reopen a filter's dialog box to change settings, simply double-click the filter name in the Layers panel.
Smart Filters can be applied only to Smart Objects. Luckily, you can convert any pixel-based layer, even a background layer, to a Smart Object simply by selecting that layer in the Layers panel and choosing Layer→Smart Objects→Convert to Smart Object. You can even select multiple layers in the Layers panel and create a single Smart Object with that command.
You can then apply a Smart Filter to all of the layers in the Smart Object. If you later need to alter the content of the Smart Object itself, double-click it in the Layers panel. The Smart Object’s contents opens in a separate image window.
After making the necessary changes, use the Save command (not Save As) and then close the window. The Smart Object will be updated in your artwork and any Smart Filters will be reapplied.
Because you can easily remove or change Smart Filters, they provide you with a special sort of creative license: the license to experiment and change your mind.
Because they are nondestructive (they don't make permanent changes to the pixels in your image), you can use Smart Filters without fear of damaging your image. Of course that doesn't mean you shouldn't work on a copy of your beautiful photo — it's always better to safeguard the original image file and work on a duplicate.