Lenses and sharpening
Sometimes a soft lens can be very effectively compensated by some
unsharp mask in post processing and you get a sharp, natural looking image. But sometimes no matter how much sharpening you apply or what parameters you choose, you get that unnatural, "sharpened" look. 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. 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). 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? -- 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 |
Lenses and sharpening
On 2014-09-13 07:23:17 +0000, Alfred Molon said:
Sometimes a soft lens can be very effectively compensated by some unsharp mask in post processing and you get a sharp, natural looking image. But sometimes no matter how much sharpening you apply or what parameters you choose, you get that unnatural, "sharpened" look. 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. 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). 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? First are we talking sharpening in general, sharpening to overcome softness due to exposure settings, or issues with a particular lens? Next, if it is a particular lens which lens? If you are talking about the 70-300mm, what brand and model, and mounted on which camera? Is the softness you are experiencing over the entire image, or edge softness? What post processing tools/software are you using? Are these RAW image files or JPEG? When in your workflow do you usually apply any particular sharpening method? -- Regards, Savageduck |
Lenses and sharpening
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. But sometimes no matter how much sharpening you apply or what parameters you choose, you get that unnatural, "sharpened" look. 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. 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). 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? Sharpening up the focus can be done to a limited extent. UnSharp Mask is probably the most limited of various sharpening tools. Likewise any sort of "smart sharpen" that tries to isolate tonal edges will be less useful. A true (not what Adobe labels as HP) high pass sharpen tool will be fairly good. The problem is that most image editors do not let the user set all the parameters, and often limit user configuration to just an amount. One better option might be wavelet sharpen. But probably the most useful would be Richardson-Lucy Deconvolutional sharpening. Using just standard default filters (Gaussian and perhaps exponantial) for the point spread function should work better than other sharpen tools, but it would also be possible to develop a very accurate point spread function for any given specific lens (think of the Hubble Telescope), and that would be very significantly better than other methods. -- Floyd L. Davidson http://www.apaflo.com/ Ukpeagvik (Barrow, Alaska) |
Lenses and sharpening
In article 2014091300481511547-savageduck1@REMOVESPAMmecom, Savageduck
says... First are we talking sharpening in general, sharpening to overcome softness due to exposure settings, or issues with a particular lens? Over- or underexposure do not cause softness. This can come from incorrect focus, a soft lens or camera shake. Next, if it is a particular lens which lens? If you are talking about the 70-300mm, what brand and model, and mounted on which camera? Is the softness you are experiencing over the entire image, or edge softness? What post processing tools/software are you using? Are these RAW image files or JPEG? When in your workflow do you usually apply any particular sharpening method? The files usually are RAW. I don't have ready made examples. It's just something I have observed over time, that sometimes image softness can be very effectively eliminated with some sharpening, sometimes not. -- 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 |
Lenses and sharpening
In article , Floyd L. Davidson says...
But probably the most useful would be Richardson-Lucy Deconvolutional sharpening. Using just standard default filters (Gaussian and perhaps exponantial) for the point spread function should work better than other sharpen tools, but it would also be possible to develop a very accurate point spread function for any given specific lens (think of the Hubble Telescope), and that would be very significantly better than other methods. If the softness is caused by a particular camera-lens combination, is there a way to determine this point spread function with for instance some calibration steps, and then apply the right sharpening/ deconvolution? I'm even wondering if this point spread function could be determined from an image (without any previous camera/lens calibration), so that the image processing software can choose the right sharpening algorithm and parameters. -- 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 |
Lenses and sharpening
Alfred Molon wrote:
In article , Floyd L. Davidson says... But probably the most useful would be Richardson-Lucy Deconvolutional sharpening. Using just standard default filters (Gaussian and perhaps exponantial) for the point spread function should work better than other sharpen tools, but it would also be possible to develop a very accurate point spread function for any given specific lens (think of the Hubble Telescope), and that would be very significantly better than other methods. If the softness is caused by a particular camera-lens combination, is there a way to determine this point spread function with for instance some calibration steps, and then apply the right sharpening/ deconvolution? 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. And in fact using a Gaussian spread will work rather well for a slight defocus problem, for diffraction, and for "haze" from atmosphere. I don't know for sure, but seem to remember that there is software available that will measure motion blur and might be able to produce a custom point spread function to counter it. I'm even wondering if this point spread function could be determined from an image (without any previous camera/lens calibration), so that the image processing software can choose the right sharpening algorithm and parameters. Some aspects might be. To really do it right though you'd need to have the lens on an optical bench, or have some very specific design specifications. But sharpening by inspection using a default Gaussian blur for the point spread function does do a fairly good job of sharpening. I'm sure you can use Google to find software that will let you try it. GIMP can do it with a GMIC plugin. -- Floyd L. Davidson http://www.apaflo.com/ Ukpeagvik (Barrow, Alaska) |
Lenses and sharpening
In article ,
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. But sometimes no matter how much sharpening you apply or what parameters you choose, you get that unnatural, "sharpened" look. 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. 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). 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? Defects in lenses rarely produce a Gaussian blur or haze that can be corrected with an unsharp mask. It's a complex mess with too many variables to compensate for. It's better to buy a higher quality lens if you're spending lots of time on correction. Some mid-range lenses can be nearly perfect within a reduced range of aperture and focal length. Sharpness charts can help you decide what works for you. Around f/2, stabilization becomes more practical than a larger aperture for low light hand-held photography. If you're talking about the Canon 70-300 DO IS USM, there's a magic aperture somewhere near f/6. The next step is to apply a small amount of a large diameter unsharp mask to remove the haze. Don't let the camera use small apertures. 300m at f/40 takes a picture of the fresnel lens :P -- I will not see posts from astraweb, theremailer, dizum, or google because they host Usenet flooders. |
Lenses and sharpening
On 2014-09-13 20:18:05 +0000, Alfred Molon said:
In article 2014091300481511547-savageduck1@REMOVESPAMmecom, Savageduck says... First are we talking sharpening in general, sharpening to overcome softness due to exposure settings, or issues with a particular lens? Over- or underexposure do not cause softness. Agreed. However, aperture setting can play a part, and shutter speed can play a part when it comes to shake or motion blur. This can come from incorrect focus, a soft lens or camera shake. Characteristics of a particular lens exhibiting softness is one thing, chronic OoF issues another. First eliminate situational, shooter error for any particular images. If this is an issue unique to a particular lens, it might be time to find out what others have experienced with that lens/camera combination, and what if any solutions they were able to reach. Who knows, perhaps a lens focus calibration is in order. Camera shake is quite obvious is something else all together, and I wouldn't describe that particular aberration as "softness". One of the most common causes of shake beyond the shooter's ability to hold steady, is gusty wind. Depending on the tools you have handy for post, some camera shake can be neutralized. In PS there is the *Shake Reduction* filter, which with the right image can improve things, but it doesn't always do the trick, and takes a little practice to get right. Other software might have some equivalent motion blur correction ability. Next, if it is a particular lens which lens? If you are talking about the 70-300mm, what brand and model, and mounted on which camera? Is the softness you are experiencing over the entire image, or edge softness? What post processing tools/software are you using? Are these RAW image files or JPEG? When in your workflow do you usually apply any particular sharpening method? The files usually are RAW. I don't have ready made examples. It's just something I have observed over time, that sometimes image softness can be very effectively eliminated with some sharpening, sometimes not. ....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. Also when there is no obvious OoF issue, and depending on the software you are using, the softness issue can be ameliorated, or even taken advantage of in post. -- Regards, Savageduck |
Lenses and sharpening
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? -- 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 |
Lenses and sharpening
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. -- 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 |
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