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#11
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Lenses and sharpening
On Sun, 14 Sep 2014 09:33:29 +0200, Alfred Molon
wrote: In article , Floyd L. Davidson says... Any good optical engineer could work it out, given the right equipment and a fairly fat check. That's not a likely route for any but the most serious and well healed. I'm wondering if the lens manufacturer could measure the point spread function for its lenses and provide this information to image processing applications, so that these could calculate the optimal sharpening function. In other words, software would compensate (at least partially) for the weaknesses of a lens, as it is being done with vignetting or geometric distortions in cameras. I suspect that DxO does something like this: otherwise they could operate ytheir 'Lens Sharpness' control of which they say: "Lens softness compensates for the difference in sharpness between the the center of the image, which is always better, and the edges, where it is softer". -- Regards, Eric Stevens |
#12
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Lenses and sharpening
On Mon, 15 Sep 2014 09:06:44 +1200, Eric Stevens
wrote: On Sun, 14 Sep 2014 09:33:29 +0200, Alfred Molon wrote: In article , Floyd L. Davidson says... Any good optical engineer could work it out, given the right equipment and a fairly fat check. That's not a likely route for any but the most serious and well healed. I'm wondering if the lens manufacturer could measure the point spread function for its lenses and provide this information to image processing applications, so that these could calculate the optimal sharpening function. In other words, software would compensate (at least partially) for the weaknesses of a lens, as it is being done with vignetting or geometric distortions in cameras. I suspect that DxO does something like this: otherwise they could operate ytheir 'Lens Sharpness' control of which they say: "Lens softness compensates for the difference in sharpness between the the center of the image, which is always better, and the edges, where it is softer". Let's try that again: I suspect that DxO does something like this: otherwise they could not operate their 'Lens Sharpness' control of which they say: "Lens softness compensates for the difference in sharpness between the the center of the image, which is always better, and the edges, where it is softer". -- Regards, Eric Stevens |
#13
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Lenses and sharpening
In article ,
Alfred Molon wrote: In article 2014091316132932858-savageduck1@REMOVESPAMmecom, Savageduck says... ...and what PP software, & what sharpening methods do you use? I am not going to advocate one application, or method over the other, I know what advice I can give with what I am familiar with in my workflow. Isn't unsharp mask the same across all PP applications? I would have thought it's an algorithm which is implemented in various PP applications, or are there differences? The digital form of unsharp mask is the inverse of a blur. There's both a frequency (diameter) and an intensity. The fancier sharpening tools analyze an image and adapt the sharpening to different types of blur in the image. This handles minor focus problems, simple motion blur, and some of the radial blurring found in cheap lenses. The super-fancy tools will trace camera shake and estimate a corrected image. -- I will not see posts from astraweb, theremailer, dizum, or google because they host Usenet flooders. |
#14
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Lenses and sharpening
Kevin McMurtrie wrote:
In article , Alfred Molon wrote: In article 2014091316132932858-savageduck1@REMOVESPAMmecom, Savageduck says... ...and what PP software, & what sharpening methods do you use? I am not going to advocate one application, or method over the other, I know what advice I can give with what I am familiar with in my workflow. Isn't unsharp mask the same across all PP applications? I would have thought it's an algorithm which is implemented in various PP applications, or are there differences? The digital form of unsharp mask is the inverse of a blur. There's both a frequency (diameter) and an intensity. Not the case. It is the high pass sharpen tool that is the inverse of blur. They can use the exact same algorithm with different parameters. Using one and then the other virtually reverses the results. UnSharpMask is not reversible. The fancier sharpening tools analyze an image and adapt the sharpening to different types of blur in the image. This handles minor focus problems, simple motion blur, and some of the radial blurring found in cheap lenses. The super-fancy tools will trace camera shake and estimate a corrected image. -- Floyd L. Davidson http://www.apaflo.com/ Ukpeagvik (Barrow, Alaska) |
#15
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Lenses and sharpening
In article , Floyd L. Davidson
wrote: UnSharpMask is not reversible. it is with a non-destructive workflow. |
#16
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Lenses and sharpening
In article , Kevin
McMurtrie says... The super-fancy tools will trace camera shake and estimate a corrected image. Which would these be? -- Alfred Molon Olympus E-series DSLRs and micro 4/3 forum at http://tech.groups.yahoo.com/group/MyOlympus/ http://myolympus.org/ photo sharing site |
#17
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Lenses and sharpening
On 13/09/2014 08:23, Alfred Molon wrote:
Sometimes a soft lens can be very effectively compensated by some unsharp mask in post processing and you get a sharp, natural looking image. For this to work well some very restrictive conditions have to be met - notably that the entire image is uniformly blurred by a symmetrical and spatially invariant point spread function (or one which varies slightly and in a very predictable way with distance from the optic axis). But sometimes no matter how much sharpening you apply or what parameters you choose, you get that unnatural, "sharpened" look. Anywhere that was already sharper to begin with than the presumed blur will end up looking unnatural with ringing artefacts around it. It probably depends on the unsharpness of the lens, its (spatial) frequency response or whether the sharpness is caused by the lens glass itself (i.e. lens not being sharp enough), inaccurate focus or some motion blur. You can only take out motion blur by modelling it. It can be done for a price provided there is something in the image to play guess the blurring function from. Used in car number plate recognition sometimes. http://www.maxent.co.uk/example_1.htm "Blind" deconvolution can also be done on larger images provided that the blurring function is pretty much the same over the entire image. For instance I have a 70-300 lens which at the tele end generates a bit soft images, which however respond well to unsharp masking in post- processing. But that's not the case for the another lens I have (a mid- range one). A lens which scatters a bit of light into a halo around everything migth well tune up OK with a bit of unsharp masking. Has somebody analysed this (i.e. how to best sharpen an image, what unsharpness can be eliminated in post-processing)? Is there perhaps some web page with details? Astronomers have the most detailed instructions on how to deconvolve images to obtain the maximum information about the night sky from finite sized and imperfect instruments. They have one big advantage over conventional photography in that their targets are all at infinity. A rough rule of thumb is that at the highest signal to noise you can get 3x the spatial resolution on the highlights and brign the noise under better control in the mid range. The price you pay is some unfamiliar artefacts in the image which can be a nuisance in medical diagnostics where practitioners are very familiar with the quirks of the standard linear inverse methods for image reconstruction. Depth of field issues make life very difficult for normal photography. -- Regards, Martin Brown |
#18
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Lenses and sharpening
On 14/09/2014 08:30, Alfred Molon wrote:
In article 2014091316132932858-savageduck1@REMOVESPAMmecom, Savageduck says... ...and what PP software, & what sharpening methods do you use? I am not going to advocate one application, or method over the other, I know what advice I can give with what I am familiar with in my workflow. Isn't unsharp mask the same across all PP applications? I would have thought it's an algorithm which is implemented in various PP applications, or are there differences? Unsharp mask historically was implemented by physical means to allow very high contrast images to be more satisfactorily be represented on printed media. It got adopted by David Mailn of the AAT to bring out faint low contrast details in nebulae that would otherwise be invisible. http://en.wikipedia.org/wiki/David_Malin And from there it entered mainstream digital image processing. It was in use for advertising purposes for quite a while prior to that. The details of most algorithms are roughly similar but how they handle underflow and overflow of pixel values may vary with implementation. -- Regards, Martin Brown |
#19
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Lenses and sharpening
nospam wrote:
In article , Floyd L. Davidson wrote: UnSharpMask is not reversible. it is with a non-destructive workflow. I'm sorry that you don't understand the meaning of that. -- Floyd L. Davidson http://www.apaflo.com/ Ukpeagvik (Barrow, Alaska) |
#20
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Lenses and sharpening
In article , Floyd L. Davidson
wrote: UnSharpMask is not reversible. it is with a non-destructive workflow. I'm sorry that you don't understand the meaning of that. i absolutely do know the meaning, since it's all i use. it's you who doesn't understand what a non-destructive workflow means and as a result, says stupid **** like what you just did. with a non-destructive workflow, unsharp mask (or anything else for that matter) can be altered or removed after the fact. that's why it's called a non-destructive workflow. |
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