Essential Darkroom

SI Pro v2.5- Stair Interpolation Pro
PC and Mac

Introducing the SI Pro v2.516-bit series

Taking image interpolation to the next level

The new SI Pro v2.5 plugin, now compatible with Photoshop CS3 and Windows Vista, gives photographers access to powerful and flexible options for customizing their own image interpolation outputs. It is the result of many months of development and based on the feedback we received from many professional photographers looking for the highest quality print output. The SI Pro v2.5 plugin is the next generation interpolation tool and replaces the popular SI Pro plugin. This new essential digital darkroom tool features improved algorithms, added options to choose from pre-set and custom paper sizes, pixel dimension, margins, printer resolution and even interpolates your images by scale. A powerful downsampling option was also added to SI Pro v2.5 making this plugin ideal for your interpolation and downsampling workflow.

The main concept of this professional plugin is to offer one solution for all digital files, including scanned film. It works with both English and Metric unit systems, therefore encompassing any printing media available.
Fine, Normal and Coarse SI Interpolation intensities as well as optional smart sharpening can also be added to your desired interpolation method. For your high ISO files, the new SI Pro v2.5 offers the option of removing color noise while preserving pixel information intact.

*8 or 16-bit color depth available for Photoshop 6, 7, CS, CS2 and CS3. Photoshop Elements versions will work with 8 bit files only.


Note: PC version illustrations will be shown throughout this pagel. Identical features are available for Mac users.


SI Pro v2.5 main features:

  • 100% compatible with CS3 and Windows Vista.
  • New simple and intuitive graphical interface.
  • Choose from 3 interpolation intensities: Fine, Normal & Coarse.
  • Carefully calibrated for your image's interpolation or downsampling needs.
  • Option to "Reduce Color noise" in order to achieve greater interpolation results (Especially when used with high ISO files)
  • English and Metric unit support.
  • Choose from Size for Paper (In inches, mm or cm), Set Image size (in pixels) and Size by Percentage (%).
  • Ability to "Save", "Load" and "Delete" custom SI Pro v2.5 profiles.
  • Eight pre-set popular paper sizes included. Option to input your own custom paper size.
  • Add Margins to your final output.
  • Works with any printer resolution easing your interpolation workflow.
  • Add smart sharpening to your final output whenever needed (Optional)


Launching the SI Pro v2.5 Plugin

Note: PC version illustrations are shown throughout this manual. Identical features are available for Mac users.

After the installation of the SI Pro v2.5 plug-in is complete, launch Photoshop. Now, you are ready to run the plug-in. Go to File/Automate and click on SI Pro v2.5:

If you are using Photoshop Elements, the plugin location is: File / Automation Tools / SI Pro v2.5

When clicking on 'SI Pro v2.5', the plugin interface will launch.
PC version shown below:

SI Pro v2.5 plug-in interface

Settings: SI Pro v2.5 allows photographers to save and load their own custom settings. You will be able to create as many SI Pro v2.5 settings (profiles) as desired to ease your workflow. In the example below, you can see that I have saved settings for different projects:

How to save custom SI Pro v2.5 settings:
In the example above, SI Pro v2.5 was set with the following options:

  • Interpolation = Normal SI
  • Sharpening Level = No Sharpening
  • Reduce Color Noise = (Unchecked)
  • Size Method = Size for Paper
  • Paper Size = Preset (30x20 Inches) - calculated for the file aspect ratio.
  • Margin = 0.25 inches

In order to save these settings for future use, I clicked on the "Save" button and created a custom setting called: "Wedding 07-12-05". If you would like to back-up your custom settings, you can find them using the following path. Every setting you create will be added to this path automatically.

For Photoshop 6.0, 7.0, CS, or CS2:
Photoshop X.X > Plug-Ins > FM Plugins > FM Settings > SI Pro v2.5 setting


Interpolation Intensities and sharpening levels (Works with any of the above SI interpolation methods)

The default sharpening setting for SI Pro v2.5 is 'No sharpening'. However, you can add special formulated sharpening to your images during SI interpolation. Two sharpening option are available: Low and High sharpening.

There are three (3) built-in Stair Interpolation intensity options. The intensity 'Normal SI' is the recommended default setting. It will run faster and provide excellent results. For even finer Interpolation, use the 'Fine' option. SI Interpolation using the Fine option may take a longer time to complete and it's not recommended for slower systems. I also advise not using 'Fine SI' with any sharpening option. The Coarse setting will provide the fastest performance and great image quality. (It's a good compromise in regards to speed and image quality.)

Original Size window: The Original Size field shows your original file setting, which is an important reference before running SI Pro v2.5. Example:

Pixel Dimensions: 3500 X 2595 Pixels (Original Width X Height)

Document Size: 11.67 X 8.65 Inches (Original Width X Height)

Resolution: 300 Pixels/Inch (PPI)

Units: This drop-down box will let you change the entire SI Pro v2.5 Unit from English to Metric. All entered settings will be converted automatically.

Reduce Color Noise option:

By checking this option, SI Pro v2.5 will reduce your file's color (chroma) noise before interpolating it.


Sizing method:

Three (3) powerful and flexible SI Pro v2.5 interpolation methods are available. Photographers can choose from:

Size for Paper (Inches, centimeters or millimeters)

This is the most powerful SI Pro v2.5 interpolation method offered. You will be able to enter the exact document size for printing output. In this example, with an input of 26.97 inches width, the image height was automatically calculated based on the image aspect ratio. Note: Most digital SLR cameras support the 3:2 aspect ratio. The aspect ratio 4:3 is usually supported by consumer digital cameras.

In the above example, I chose a 3:2 aspect ratio digital file on a 30 X 20 inch media. As you can see, 26.97 inches will be added to the width in order to support this aspect ration. In order to fill out the entire paper, cropping your image before running SI Pro v2.5 may be needed.

Next, I entered 300 Pixels/Inch (PPI) resolution. This is the output resolution and varies depending on your printing output device. Finally, I added a 0.25 inch margin. (This is a great time saver if you don't have a borderless printer.)

With SI Pro v2.5, you can choose from your own custom sizes or select from a list of popular pre-set media outputs. They are:

Set image size

If you already know your desired output dimension size in 'pixels', then method 2, 'Set image size' may be used. In the above example, I added 6500 pixels width. The height of 4819 pixels was calculated automatically based on the original image aspect ratio.


Increase image by Percentage (%)

What is the difference between Custom Resize Pro series of plugins and the new SI Pro v2.5 plugin?

Each plugin has an entirely different technique and approach to image interpolation. The SI Pro v2.5 plugin uses a unique and now improved stair interpolation method and therefore works with any digital file including cropped, already interpolated images, or scanned film. On the other hand, the Resize pro plugins will only work optimally with the camera file it was designed for. It increases image size based on pixel contrast and therefore needs the original camera file, free of sharpening (Including in-camera) to achieve superior results. So, if you have more than one digital camera, shoot film, severely crop images, or sharpen before interpolation, then the SI Pro v2.5 plugin is the best tool for you. (Keep in mind that any interpolation method works best with unsharpenened files)




Everyone involved with digital imaging has heard about Genuine Fractals. This utility claimed to do a better job interpolating digital images than Photoshop's bicubic engine. SI Pro v2.5 uses a different approach to Fractals, which allows interpolated files to maintain a high level of detail while keeping your photograph's natural look. (Without the creation of fractal artifacts) - It's also only a fraction of the price. :-)

Using the Stair Interpolation Pro 2 Plugin, will make your interpolated images appear sharper, therefore producing beautiful prints. After running the plugin, SI Pro v2.5 images are superior to Genuine Fractal's and much better than just using Photoshop Bicubic (Or Bicubic Smoother) alone.

Here are a few cropped samples:
Note: Image increase by percentage is only one of many SI Interpolation methods provided by this plugin.

150% image increase

Genuine Fractals v2.0 

 SI Pro v2.5


200% image increase

 Genuine Fractals v2.0 

  SI Pro v2.5


300% image increase

  Genuine Fractals v2.0

   SI Pro v2.5