Uncoded wide-angle lenses produce on Leica cameras cyan vignetting. Unfortunately, in many other system cameras too. These colored vignettes are more or less on strong. At the Sony NEX less, but for example on my EOS-M is very strong. A few days ago I had the fantastic Voigtlander Super Wide Heliar 15mm f/4.5 to get. Even with the first shots the pink corners appeared in the pictures. Of course you can crop the image. But why would I need a wide angle lens?
The solution is CORNERFIX. This is a freeware that is able to remove any vignetting from the images. But there's a catch. The program only works with DNG files. DNG means "digital negative" . This is a raw data format for photos, which was introduced in 2004 by Adobe. Some cameras use natively already the DNG format, for example Pentax and Samsung. Most other cameras have their own raw data (Canon has CR2, Nikon NEF). It is therefore essential to shoot in raw format. The photos must first be converted to the DNG format. For this purpose you can use Adobe Photoshop or Adobe Lightroom. Those who do not have these programs that can use the free Adobe DNG converter. Lightroom includes in his library-function its own instruction set only to convert to DNG. It's very comfortable. You can even convert whole folders in one go. Great thing!
OK. How do you work now with CORNERFIX?
Make sure your reference image is overexposed (to a maximum of two steps EV). It may also be blurred, which is no problem with manual lenses. Yesterday I made my reference image with an old gray school stapler. Because my gray card is yet to come in the mail in the next few days. This is my reference picture:
Open the file "cornerfixw" and then "Lens profile -> create". Search in window that opens your reference picture and upload it into the program. Then save it on "Lens profile -> save as". It is generated a file of type ". cpf" . Rename the file with the name of the lens, then you can find the file again and again quickly. I named my file "voigtlaender_15mm.cpf". So the hardest thing done.
If you now want to free photos of the vignetting, then proceed as follows:
1. Open CORNERFIX
2. Upload your reference image (Lens profile -> open). Note that the image is uploaded but not displayed.
3. Open your file with (File -> open image). If you want to edit multiple photos at the same time, then go to (File -> Batch correct images). Cornerfix works fully automatic.
4. Save the final image under (File -> save image). When batch processing, the program will automatically save your corrected files ending with "CF".
The corrected photos are in DNG format. You can then edit any further. Here you can see, how CORNERFIX works: first the original picture with cyan vignettes, second the final corrected picture.