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Archive 2012 · A thread about Cornerfix
  
 
Jacob D
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p.1 #1 · A thread about Cornerfix


This thread is to discuss all things related to using the Cornerfix program.



From the Cornerfix Website:
"
CornerFix corrects for vignetting effects in digital images. It's most often used to correct for the color vignetting that occurs when wide angle lenses are used with digital sensors that include IR filters, resulting in so-called "Cyan Corners".
"



(Cyan Corners also known as color shift around the FM forum here)

This will probably be mostly relevant to Leica M9, and Sony NEX users, but possibly others as well. The use of wide angle rangefinder lenses on certain sized sensors is generally the culprit leading to color shift. There are several methods of dealing with color shift, each will produce different results.

My purpose of starting this thread was to (A) Learn more about correcting color shift in images using Cornerfix, and (B) To help others find this information.


I will start by posting the steps that I use to create an image profile, as well as those to correct images. I am NOT an expert on this subject. Whatever I may post has been learned and cobbled together from various forum members here, the Cornerfix website, and around the web. Hopefully through sharing experiences we will all be able to learn something and become experts on the subject.




Feb 07, 2012 at 07:16 PM
douglasf13
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p.1 #2 · A thread about Cornerfix


Fantastic! My first child is due any day now, so I'm a little bogged down right now, but I'd like to contribute at some point. In the meantime, I look forward to hints and tricks from others, as I've definitely not mastered the program.


Feb 07, 2012 at 07:18 PM
Jacob D
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p.1 #3 · A thread about Cornerfix


All though I am posting this as a "how to" it is simply the process I have arrived at as of today. I would suggest this can be a starting point for anyone not familiar with Cornerfix. With some time this may evolve into a more refined process.

You must obviously download the Cornerfix program to attempt this. The link is above in the first post.



CREATING PROFILES

1. Set camera mode to A, focus your lens to infinity and stop down to whatever aperture you plan to use for making the profile (you may need to make a profile for various apertures if your lens shows significant difference between them).

2. Set exposure compensation to +2 EV. Focus to infinity.

3. You will need a piece of white tissue, or better yet, semi-opaque white plastic. Find a location with a clear view of the sky and aim in the direction of most even illumination. While holding the white tissue/plastic in front of the lens (but not touching) and snap a shot.

4. Import the photo to your editor.

5. Check for dust spots (max out the black level, contrast, and clarity to help spots more easily) and remove any that you find.

6. If you changed any image settings in the previous step, return them to their defaults, then white balance the image using the approximate center for the WB sample.

7. Export the file to DNG format. Rename it so you know which lens and aperture it corresponds with.

8. Open Cornerfix.

9. From the FILE menu, choose OPEN, and select the DNG file that you just created. Wait a few seconds while Cornerfix builds a thumbnail, then...

10. From the OPTIONS menu, choose PROFILE CREATION OPTIONS. Only the MULTIPLE EQUATIONS option should be ticked, click OK. This will cause profile creation to take longer, but should choose the best equation to generate your profile from. It will not affecting the time it takes to correct photos when the profile is later on.

11. From the LENS PROFILE menu, choose CREATE. Cornerfix will run for a minute or two. When the message in the bottom window reads "Processing complete" go to the next step.

12. From the LENS PROFILE menu, choose SAVE AS, and save the profile in a location you can easily find it again.

13. Return to the OPTIONS menu, choose PROFILE CREATE OPTIONS. This time MULTIPLE EQUATIONS and LUMINANCE COMPENSATION should be ticked, click OK.

14. Repeat steps 11 & 12, when saving the profile this time add something such as "lum-comp" to the file name.

15. You now have 2 profiles that can be used to correct images from your lens (whatever lens it might have been). They will give slightly different results so you may wish to try both to see which you prefer.





CORRECTING IMAGES

1. Before opening any images, there are a couple of options you may be interested in... from the OPTIONS menu, choose IMAGE CORRECTION OPTIONS. The CHROMA and LUMINANCE values can be fine tuned if need be. CHROMA deals with removal of color shift whereas LUMINANCE deals with removal of vignetting. If vignetting is not something you want to be corrected, set the value to 0.

2. Ok, the image must be a .dng file, if you have not converted to DNG format, do so now.

3. From the FILE menu, choose OPEN, and locate the .dng file that you created.

4. Cornerfix will open your image and create a preview.

5. From the PROFILES menu, choose OPEN and locate the profile that you want to use (see above section if you have not created a profile yet).

6. Cornerfix will begin the correction process. When correction is complete the preview will appear on the right side of the screen.

7. The preview quality is only so-so, but you should be able to get a rough idea how the color shift correction looks.

8. If you're not happy with the result try fine tuning the IMAGE CORRECTION OPTIONS, or use an alternate profile if you have one.

9. If everything looks fine, then rejoice in your corrected image, but make sure to save it before you quit! From the FILE menu, click SAVE IMAGE, then save it. All done!





Feb 07, 2012 at 07:20 PM
Jacob D
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p.1 #4 · A thread about Cornerfix


I would also like to add a couple of thoughts before I sign off to other chores for the day...

- I have experimented with making profiles at different luminance values and used them to correct a test image. I saw very little, if any difference in the end result. I was a little surprised by this, but the program seems to compensate. I think it is probably best to stick with the direction supplied on the Cornerfix website and use +2 EV to generate profiles.

- I recently found a couple of images that refused to be corrected, or at least were not corrected to the extent I had wanted. Both images were taken near the beach with blue sky, blue water, and heavy shade... in other words, they had an overall "cool" color tone. I don't know if this cased some issue or not.

When I have a bit more time I'll post those images, as well as some that I have corrected for comparison.

I look forward to hearing others' experience and workflow (also how you work this into your workflow).



Feb 07, 2012 at 07:28 PM
douglasf13
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p.1 #5 · A thread about Cornerfix


I think many of us, myself included, may need Cornerfix more than we may realize with the 5N. For example, here is a shot with the NEX-5N and ZM 35/2 wide open (or near it.) My partner is blacked out in these.







At first glance, this shot doesn't scream CornerFix to me, but I think pavement is a great indicator, because it isn't supposed to have a magenta cast.

Now, here is the same shot run through CornerFix. I set Chroma to +1, and Luminance to +0, which gives the standard color fix without any vignetting reduction. Now THIS is more like what I'm used to seeing with DSLRs and film cameras:








The difference is subtle, but I'm to the point where I'm probably going to be running everything I shoot with the ZM 35/2 (and CV 15/4.5) through CornerFix, because I don't like having these magenta lowlights around the outside of my images.

Edited on Feb 12, 2012 at 02:42 AM · View previous versions



Feb 11, 2012 at 10:04 PM
Makten
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p.1 #6 · A thread about Cornerfix


I have a nice tip for getting the reference image: Set the lens at infinity and point it at your computer screen, while showing a white or gray frame. It will of course be waaay out of focus when you fill the camera image, so no need for anything inbetween.
I came up with the idea when I needed the reference after the sun had set and I didn't have any evenly illuminated walls or anything at home. It works very well and you can experiment with different apertures, exposures and focus settings, sitting right infront of your computer.

Edit: Maybe this should not be recommended if you got a cheap, one side illuminated screen though.

Edit 2: An other tip is to not correct dark images shot at night or at very high ISO. The increased noise in the corners will most likely look worse than the original color shift. I also suggest that you turn down the luminance vignetting correction, so that the only correction is for color shifts. Otherwise you'll get trouble with images shot at different apertures, since luminance vignetting is a function of that, but color shift is not.



Feb 11, 2012 at 10:19 PM
shelt
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p.1 #7 · A thread about Cornerfix


Great tip on the computer screen!

Douglas -- speaking of needing CF more than you think, I noticed even the Sony 16mm needs a good dose of CF on the NEX-7. I assume it's corrected for when shooting jpg...




Feb 12, 2012 at 12:07 AM
douglasf13
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p.1 #8 · A thread about Cornerfix


Hi, Makten. I tried the computer screen trick with my Macbook, but it may not be suitable, because my profiles, especially with the CV 15/4.5, come out funky.

Agreed about the vignetting. I usually process my images with the Chroma slider at +1, and then move the Luminance slider to taste. Usually 0 with the ZM 35/2, and almost +1 with my CV 15/4.5.

Hi, shelt. Yeah, it looks looks the Sony 16 does need some help in RAW.



Feb 12, 2012 at 12:49 AM
Jeff Kott
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p.1 #9 · A thread about Cornerfix


I work in Capture One 6 which doesn't recognize DNG files. I think there's a way to set a profile in C1 6 that operates the same way that Cornerfix does, but I've never tried it. If anyone has done this, I'd be interested in hearing how well he/she thinks it works and also their procedure in C1 6.


Feb 12, 2012 at 02:19 AM
 

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sirimiri
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p.1 #10 · A thread about Cornerfix


Woot, Upper Grand, up the stairs from California Plaza.
douglasf13 wrote:
http://farm8.staticflickr.com/7204/6860024713_62d1cac213_b.jpg


I need to make some cornerfix profiles shortly. FM'er Jeff Hapeman also penned an article about it that's worth looking at.

Edited on Feb 12, 2012 at 02:52 AM · View previous versions



Feb 12, 2012 at 02:23 AM
Jeff Kott
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p.1 #11 · A thread about Cornerfix


douglasf13 wrote:
I apologize to my wife for posting a throw away shot of her making a less than flattering face. This was just a good shot for demonstration purposes. Sorry, Honey!


Douglas, FYI, this wouldn't fly with my wife. We have an explicit agreement she has total discretion to make me delete any photos I take of her and pre approval rights over any that I intend to print or post. Otherwise, she'd never let me take her photo. (BTW, she's very photogenic.)



Feb 12, 2012 at 02:26 AM
douglasf13
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p.1 #12 · A thread about Cornerfix


Yeah, my wife trusts my judgement, and I rarely post pics of her, but I went ahead and blacked her out in my earlier post. She was over 8 1/2 months pregnant in that shot, so I shouldn't risk it.



Feb 12, 2012 at 02:44 AM
sirimiri
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p.1 #13 · A thread about Cornerfix


^^So congratulations are (almost) in order.


Feb 12, 2012 at 02:53 AM
douglasf13
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p.1 #14 · A thread about Cornerfix


sirimiri wrote:
^^So congratulations are (almost) in order.


Thanks. Due date was yesterday, so any time now...



Feb 12, 2012 at 03:05 AM
Jacob D
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p.1 #15 · A thread about Cornerfix


Douglas, et all... glad to see this got picked up by you guys. I'm preparing for company, then a trip out of town for a bit. I won't have anything useful to contribute for a couple of weeks


Feb 12, 2012 at 04:40 AM
Jeff Kott
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p.1 #16 · A thread about Cornerfix


douglasf13 wrote:
Yeah, my wife trusts my judgement, and I rarely post pics of her, but I went ahead and blacked her out in my earlier post. She was over 8 1/2 months pregnant in that shot, so I shouldn't risk it.


BTW, I wasn't suggesting you were doing anything wrong, I was just contrasting to my situation.


I bet as soon as the baby comes, we're going to see a lot of Sonnar pics. Good luck with everything - we're due July 1.



Feb 12, 2012 at 05:10 AM
douglasf13
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p.1 #17 · A thread about Cornerfix


Jeff Kott wrote:
BTW, I wasn't suggesting you were doing anything wrong, I was just contrasting to my situation.


I bet as soon as the baby comes, we're going to see a lot of Sonnar pics. Good luck with everything - we're due July 1.


Oh, no sweat. I just figured I'd play it safe.

Thanks for the well wishes. This is our first baby, so I'm preparing for quite a life change! Good luck to you, too!



Feb 12, 2012 at 05:55 AM
Jeff Kott
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p.1 #18 · A thread about Cornerfix


douglasf13 wrote:
[This is our first baby, so I'm preparing for quite a life change! Good luck to you, too!


It's going to be our first too. We'll have to try not to inundate the NEX Image forum with baby photos.


Of course, that's going to be difficult with the first. I was number four in my family. Tons and tons of photos of number 1, with decreasing photo coverage as you go down the birth order.
.



Feb 12, 2012 at 07:48 AM





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