Resizing Smoke & Mirrors Part 2

If yesterday was not enough to start your head spinning today we address the issue of Resample Image. First off let's define what this is. When you click on the OK button in this dialog Photoshop will resize the image based on what is selected in this field. Before we get into the options, here is a simplified example of what resampling is.

As the image is enlarged the pixels are spread apart. The area between the pixels needs to be filled in with an interpolated rendering of the adjacent pixels. Call it color averaging as a ratio of the color shift. Ok... That was a bit deep!

Now that resampling is cleared up lets move on to an even more and deeper muddy waters. The screen capture below is of Lightroom Elements (v6 at that) as I am on the road using my PowerBook G4. Why did I say that? First there is a difference between Elements and CS and second If you are familiar with the PowerBooks you will know why I am running Elements and not CS3. Anyhow the listing of the options are the same. The wording in parenthesis are what is in CS and not Elements.

   Nearest Neighbor (preserve hard edges)

   Bilinear

   Bicubic (best for smooth gradients)

   Bicubic Smoother (best for enlargements)

   Bicubic Sharper (best for reduction)

So lets take a closer look at these options.

Nearest Neighbor and Bilinear are Adobe throw-back to bygone years when Photoshop was intended for graphic designer. These are not intended for image resizing but I am sure someone out there is madly in love with their Nearest Neighbor. Actually though, if you are resizing graphics this is the better option to use.

For photo resizing it is best to live in the Bicubic Zone, think of bicubic zirconia and your work will shine like diamonds. Ok I'll get off the glass thing. With no further ado I introduce you to the bicubic spline interpolation algorithm.

RIGHT! Putting it in very simple terms, if you take the "bi" out of the word you are left with linear and cubic. Thinking dimensionally a linear surface is flat while a cubic object has depth or dimension. Bringing this back to resampling and image, the bicubic interpolation provides greater depth than bilinear interpolation.

So why does Bicubic come in three flavors? By modifying the algorithm Adobe can make Photoshop bias the process to enhance the resampling in a specific direction. In this case for smoother gradations, for enlargements and for reductions. It all depends on what you are doing. There is no perfect option for all conditions. It would be nice to see an Auto option here where PS would know what to do based on where you are and where you want it to go.

What do I use? Mostly I leave it on Bicubic (best for smooth gradients) unless I am going to make a drastic change in size. When that is the case I use onOne Software (sorry, I said it again... Oops) Genuine Fractals to resize.

Hope that helps on the resizing dialog box in Photoshop.

Take care... Doug


P.S.  When you are resizing an object with the Crop or Free Transform tool you will also be resampling that particular object. But the question arises... By which option? In Photoshop it is by the default mode you have selected in the preferences. In Elements I believe it is the last selection you have in the Image Size dialog box as there is not an option in preferences.