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Archive 2007 · Canon DPP: lens correction = soft images
  
 
srui
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p.1 #1 · Canon DPP: lens correction = soft images


Hi all,

I was comparing some photos I took when processed with Canon DPP new lens correction feature and the photos were actually softer when this correction was on...

Has anyone else experienced this? Could this be due to a EXIF hack that I made to enable this correction with my "old" Canon 350D? Do I have to due some parameter tweaking or should this work out off the box?

I'm guessing this is due to a bug in the interpolation algorithm used for the distortion and chromatic aberration correction, but how does it work with other officially supported camera models.

Best regards,

Sergio Rui Silva



Dec 12, 2007 at 05:24 PM
abqnmusa
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p.1 #2 · Canon DPP: lens correction = soft images


I suspect the lens correction is not the cause of image softening. The lens correction alone will not do that.

When you selec the nosie reduction sliders to remove noise you get a softening of the image. I normally only select LOW due to the amount of image softening. This is not unique to DPP. All noise reduction software soften the image.

Shoot RAW and expost the histogram to the right to avoid underexposure. Underexposure causes more noise, and the need to noise removal.



Dec 12, 2007 at 05:43 PM
Gochugogi
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p.1 #3 · Canon DPP: lens correction = soft images


I've only used it a few times--doesn't support most of my lenses--but I haven't noticed any softness. However the NR has indeed soften a bit so use it only if truly needed.


Dec 12, 2007 at 06:23 PM
nathanlake
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p.1 #4 · Canon DPP: lens correction = soft images


Any processing that manipulate the image has the potential for having an impact on quality. In fact, I am sure it does impact quality. Hopefully, it is minimal. I have never noticed it, but I am not surprised.


Dec 12, 2007 at 06:28 PM
srui
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p.1 #5 · Canon DPP: lens correction = soft images


No, noise reduction and sharpening setting were keep the same (Sharpness (RAW) = 5, Sharpness (RGB) = 75, Luminance Noise Reduction = Low, Chrominance Noise Reduction = Low).

Theoretically one should expect some image degradation because of interpolation, but not to this extent... I mean, the purpose is to get a better quality image and so the gain of correcting the lens faults should exceed the degradation of due interpolation...

Tweaking the "shooting distance" bar helps some what...

If only DxO had a better RAW processor...





Dec 12, 2007 at 09:32 PM
Mark Shaxted
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p.1 #6 · Canon DPP: lens correction = soft images


Lens correction and rotation destroys image quality - there's no alternative. Check out the following simple example. Original, then rotated 17.2 degrees and back again.













Both enlarged to 400% (nearest neighbour).



Dec 12, 2007 at 09:50 PM
srui
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p.1 #7 · Canon DPP: lens correction = soft images


Just made the same test using Matlab and the image you posted. You can get better results with bicubic interpolation and certainly much better with fancier interpolation kernels. Nevertheless your point is a good point: there will be always some image degradation. There is just no substitute for good distortion free optics.




Dec 12, 2007 at 10:09 PM
keith_cooper
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p.1 #8 · Canon DPP: lens correction = soft images


> Both enlarged to 400% (nearest neighbour).

And there is one of the best indications of the potential futility of looking at 100% or greater magnifications of digital images I've seen in a while :-) :-)

I've tried DPP on a 1Ds3 image taken with a 14mm 2.8L II lens. It's about more than nit picking sharpness, it corrects residual geometric distortions and virtually removes any CA, both often more important to the overall look of images I'm looking to print than any slight sub pixel deterioration. When such corrections are integrated with raw conversion then you can get results impossible after the demosaicing (although I don't know if the DPP implementation does this) 21MP has actually reminded me that there is often much more to a good image than any nominal ideals of sharpness...

I've used DxO Optics Pro in the past as a raw processor for -some- images, specifically because of the corrections it offered. Unfortunately since they don't yet support the 1Ds3, the 14mm II, or produce a version to run on my Mac, I'm stuck with DPP.

Would I rather get rid of some residual CA in tree branches against the sky, or would I worry about some miniscule loss of sharpness in some areas of the image? I know which one is more likely to show up in a real print ;-)



Dec 12, 2007 at 10:21 PM
Mark Shaxted
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p.1 #9 · Canon DPP: lens correction = soft images


Sorry - I should have said 'zoomed' 400%, just to better`see the loss of original detail.

The irony is, many folks constantly go on about the resolution of their fine L lenses, spend hours doing detailed 'test' shots of brick walls, then apply abritary rotations to correct for wonky horizons... thereby destroying all the fine detail they captured! Makes ya wonder sometimes

At the end of the day, you can't beat getting the picture right in camera - and if your lens shows minor distortions, so be it - let it be a 'feature' of the image.

Mark



Dec 12, 2007 at 10:26 PM
keith_cooper
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p.1 #10 · Canon DPP: lens correction = soft images


You're quite right about the mismatch between brick wall shots and 'real' pictures (unless you are in the brick making business I suppose ;-)

I've just added some 100% screen shots of the effect of DPP to the 14mm image I mentioned above at:

http://www.northlight-images.co.uk/article_pages/cameras/canon_1ds3_notes.html

If you mouse over the image you can see the comparison between no correction and CA+Vignetting correction at the corner of the image.

The distortion correction for this lens magnifies and flattens the image somewhat and you can see a slight softening (at 100% ;-) at the centre of the image. For my 16-35 at 16mm I'd be more likely to use the geometry correction for some interior shots, but the actual distortion of the 14 is appreciably less than the 16-35 so I might not use it at all - even the vignetting is not a problem with some landscape shots - depends on the 'look' I want...



Dec 12, 2007 at 11:37 PM
 

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gfiksel
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p.1 #11 · Canon DPP: lens correction = soft images


Mark Shaxted wrote:
Sorry - I should have said 'zoomed' 400%, just to better`see the loss of original detail.

The irony is, many folks constantly go on about the resolution of their fine L lenses, spend hours doing detailed 'test' shots of brick walls, then apply abritary rotations to correct for wonky horizons... thereby destroying all the fine detail they captured! Makes ya wonder sometimes

At the end of the day, you can't beat getting the picture right in camera - and if your lens shows minor distortions, so be it - let it be a 'feature' of the image.

Mark


Mark, could you provide the details of your test? Do you rotate the image, save, open it and rotate back? I was trying to reproduce it by rotating similar images in LightRoom, was moving the slider back and forth and the image always comes back to it's original shape without any distortion. Now, if you rotate, save, open, and rotate back it does acquire artifacts but one shouldn't manipulate images in such a barbaric fashion



Dec 13, 2007 at 12:00 AM
Mark Shaxted
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p.1 #12 · Canon DPP: lens correction = soft images


CA & Vignetting are mathmatical and operate on a per pixel basis. These operations don't degrade the image at all - in fact they actually enhance it if they produce the effects you're after.

Geometry correction is entirely different.

gfiksel... an 'intelligent' piece of software would compond all rotations/distortions into one transformation. In other words, a 10+10+10 degree rotation clockwise followed by a 30 degree rotation anti-clockwise would in effect be a 0 degree rotation... in other words a do nothing rotation. That is what you are seeing in Lightroom. If you saved between each rotation you'd see 'horrific' artifacts.

My point was that any geometric operation (ie NOT colour/contrast/saturation etc) is a very destructive process and should be avoided if at all possible. As I said above -get it right in camera.

The reason we can get away with horizon correction (for example) is simply that any given source pixel is so small in the final output (print or screen) that the effects are largely hidden. This doesn't mean they don't exist.

As per my previous post, I'm not actually advocating that you don't do geometry correction. I'm in the 'stand back at look at the whole picture camp' - is it good or bad? But too many people think that MFT chart are the be all and end all of lenses - I'm just saying that if you want to correct geometry you're giving up a 'LOT' of the detail your expensive 'L' lenses provide.

If you're a portrait shooter, maybe smudging detail is a good thing if you need to rotate or undistort(?) an image. As someone that prefers landscape photography, I'd rather keep as much detail as is possible.

Mark



Dec 13, 2007 at 12:57 AM
Mark Shaxted
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p.1 #13 · Canon DPP: lens correction = soft images


Just for the record...

Re-reading the above makes me sound anti L lens. I'm not - I own L's.

I'm just saying in a very roundabout way that the picture is more important than the methods used to create it.

Anyway - back to the port



Dec 13, 2007 at 01:01 AM
gfiksel
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p.1 #14 · Canon DPP: lens correction = soft images


Mark,
I wish people actually read a question before answering it.



Dec 13, 2007 at 05:57 PM
Rodney_Gold
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p.1 #15 · Canon DPP: lens correction = soft images


The DPP lens correction on my 5d using my 28-300L actually sharpens the image , but I only use the CA and Peripheral illumination , not the distortion correction or colour blur. NR I leave off.entirely.
I generally use DPP sharpen of 3 or 4 or sometimes - rarely , 5.
If you look at the magnfied section in the Lens abberation section , as you apply distortion correction , you can VISIBLY see the magnified image go a LOT softer when im using this lens at the wide end - and thats centre frame as well!!!
So it appears using the distortion correction does soften ther image??




Dec 13, 2007 at 07:55 PM
John Black
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p.1 #16 · Canon DPP: lens correction = soft images


Rodney - Glad to hear you say that because I think my 28-300L IS took a giant step forward with DPP 3.2 - and this is on the 1Ds2. I thought it was my imagination DPP cleans up the 28mm distortion quite nicely too.


Dec 13, 2007 at 09:01 PM
Alan321
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p.1 #17 · Canon DPP: lens correction = soft images


The DPP lens corrections can lead to image softness - the program documentation mentions it. Possibly the greatest cause is that the corrections change as the focus distance changes but very few cameras put the focus distance into the EXIF data (or elsewhere into the raw file) for the program to work with. Thus you can easily be applying a correction for the wrong distance. It doesn't help at all that DPP does not show a useful distance scale. The only distances you can hope to get right are maximum and minimum.

- Alan



Dec 15, 2007 at 10:29 AM
Larry H in GA
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p.1 #18 · Canon DPP: lens correction = soft images


I am sorry if this is a stupid question, but...

I just loaded DPP from the CD-ROM (v.3.1 if that makes a difference). I cannot find a lens correction feature. Could someone tell me where to find it?

Also, I seem to remember a thread saying there was a later version available. What functionality does it add?



Dec 16, 2007 at 04:28 PM
JDSA
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p.1 #19 · Canon DPP: lens correction = soft images


DPP seems to expand the image until the distortion at the edges is reduced. PTLens expands some parts of the image while it contracts others. It may be that DPP is causing too much stretch whereas PTLens (within CS3) averages the contrast robbing distortion accross the images and better preserves actual and perceived detail.

Which one is more accurate I cannot say. It would sure be nice if DPP included all of the math needed for most of the bodies and lenses so that the user could make the selection when the application is unable to. PTLens has done that for years.

I do like the look of DPP's way too limited distortion filter and especially the way it gets vignetting just right with one click.



Dec 16, 2007 at 08:02 PM
trumpet_guy
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p.1 #20 · Canon DPP: lens correction = soft images


Larry H in GA wrote:
I am sorry if this is a stupid question, but...

I just loaded DPP from the CD-ROM (v.3.1 if that makes a difference). I cannot find a lens correction feature. Could someone tell me where to find it?

Also, I seem to remember a thread saying there was a later version available. What functionality does it add?



It's not a stupid question at all.

You will need to go to the Canon website and download the latest version
of DPP (it is 3.2.0.4). Once you've installed that, you will see another
tab on the tool pallette called NR/Lens. That's where the new correction
stuff is.



Dec 16, 2007 at 10:31 PM
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