I love instant pack films and I love my Polaroid 360 pack film camera. I usually shoot Fuji FP-3000B and Fuji FP-100C film. The photos look great but, I must admit, they are a bit small by today's standards. While I value the uniqueness of the original Polaroid, I'd like to make enlargements, crops, etc.
Polaroid 665 positive/negative pack film which would allow a pack film camera to make negatives which can be enlarged. It's been discontinued since 2006 though stocks remain available on eBay. Still, I've found 665 to be a bit farkakte. And, while my technique is clearly no substitute for the unique look of a 665 negative, it is more practical under on-the-go conditions, IMHO.
Examine the technical data sheets for the instant film you are using and you'll find its optimal resolution listed in lp/mm (line pairs per mm). Under close inspection, the human eye cannot discern more than 5-10 lp/mm of resolution. If an instant print has 20lp/mm, then one could achieve a 4x enlargement without noticable grain, blur, or artifacts. Depending on your desired viewing distance, the subject matter, and your skill in selective sharpening, one could go a few times higher.
It doesn't seem like much but, thankfully, our film size is larger than 35mm! A 4x enlargement of instant pack film yields a 13" x 17" print.
Note: I use Photoshop. You can use the GIMP. Either way, there are many different paths to achieving the same goal. Let's not pick nits. If you have your own method, go ahead. The overall steps and the end goal are what is important.
Step 1: Scan your photo. Remember GIGO (Garbage In, Garbage Out). You don't need an amazing expensive scanner but you do need more than a multi-function print/scan/fax device. An Epson 4490 or 4990 or better will do a great job. I like to do a 2x oversampling to account for all the processing we'll be doing to the photo. I print at 300DPI, So, if I want a 4x enlargement I'll scan at 2400DPI (300DPI x 4 x 2).
Step 2: Remove Dust and Scratches. Duplicate the image in Photoshop onto a second layer and run Dust and Scratches. Then use the eraser to restore lost detail in key locations. Clear up dust and defects on the remainder of the image by hand.
Step 3: Levels, Curves, Burn, Dodge, Crop. Apply standard adjustments to account for the scanner, your output, etc.
Step 4: Flatten and Resize. I send my photos out to MPIX.com for printing on Ilford B&W paper. They print at 240DPI. If you were using an inkjet for output, you might choose a higher resolution like 600DPI.
Step 5: Selective Sharpening. Duplicate the image and copy to a second layer. Then make it invisible and move to the first layer. Apply Unsharp Mask to taste on your image. Then make the second layer visible. Use the eraser with varying opacity and hardness to the important elements of your image. By only sharpening important elements such as the eyes, hair, and edges, you will create a sharp looking image that doesn't appear over-processed.
That's it. Now you can have the best of both worlds. Get an instant print and get fantastic looking enlargements that everyone will hang in their homes.
Comments always welcome.