Luminous Landscape Forum
Raw & Post Processing, Printing => Printing: Printers, Papers and Inks => Topic started by: wolfnowl on January 06, 2010, 02:42:47 am
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from Mike Johnston's 'The Online Photographer (http://theonlinephotographer.typepad.com/the_online_photographer/2010/01/how-sharp-is-your-printer-how-sharp-are-your-eyes.html)' page...
Interesting read...
Mike.
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from Mike Johnston's 'The Online Photographer (http://theonlinephotographer.typepad.com/the_online_photographer/2010/01/how-sharp-is-your-printer-how-sharp-are-your-eyes.html)' page...
Interesting read...
Mike.
While I do not think much will be changed in the conclusion that 450 PPI input is the optimal input for best image quality possible in a print, it might be a better method to keep up- and downsampling limited to one step in the process. The method as described uses two steps and possibly two different algorithms to get to native printer input resolution. There's no mention of smart print sharpening which could make a difference too.
met vriendelijke groeten, Ernst Dinkla
Try: http://groups.yahoo.com/group/Wide_Inkjet_Printers/ (http://groups.yahoo.com/group/Wide_Inkjet_Printers/)
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This is an interesting approach, but I question how much will be visible in thumbnails. I recommend 8 x 10 prints of unfamilar subjects and compare no more than three steps (in octaves, e.g. 180, 360, 720) at a time. In fact, I'd skip the lowest octave and go to the next two higher. Then repeat for each media you use.
As I've mentioned before, manufactuer claims about print resolution are fairly meaningless above 600 dpi. If the Epsons and Canons would be forthcoming about how their upsampling algorithims work, then we could all form educated opinions about upsampling to the "printer resolution".
There are a lot of variables in play here. My simpler advice: find a resolution that works with your printer, your media, your finished print size and your subject matter. Don't worry about it being too high-we are long past the era of worrying about computer memory resources. Stick with it until you have a compelling need to change, whether that reason is ink set, printer, media, or print size.
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Interesting read...
"Interesting" perhaps...but filled with some "wrongess" for sure...
Resampling anything anywhere will have an impact down the road when it comes time to sharpen...which by the way the author failed to address at all. (the failure to even address resampling for the contact sheets and the use of output sharpening for the printing makes this whole test nothing other than mildly "interesting").
The other main part of the equation that the author seems to have glossed over (since he may not understand it) is the issue of print SIZE and the human eye's visual acuity (loosely called "resolution").
It's not easy to compare the "PPI/DPI" of human vision to printed output but you can. Human visual acuity is generally defined as being capable of resolving a spacial design whose features are separated by one minute of arc (or 1/60th of a degree). What that one minute of arc represents is entirely dependent on viewing distance. The eye can see more resolvable detail closer than further away (assuming you don't bee reading glasses–all of this is based upon 20/20 vision).
Given that 1/60th is 0.00029089 radian, you can calculate the threshold of visual acuity for a given distance. Calculate the limit L of visual acuity at distance D with this formula L=D*TAN(0.00029089).
What this will give you is the following viewing distance and resolution required table:
Viewing Distance (inches)____ Limit (inches)______Resolution (DPI)
8 _______________________ 0.00232 ______________ 428
12 ______________________ 0.00349 ______________ 286
15 ______________________ 0.00436 ______________ 229
18 ______________________ 0.00524 ______________ 191
20 ______________________ 0.00582 ______________ 172
24 ______________________ 0.00698 ______________ 143
A couple of things related to the above...these are not my numbers but Bruce Fraser's numbers from his Real World Image Sharpening book )both the original and the one I updated). But since I'm coauthor of the current edition I stand by them (I was also the guy who asked Bruce the original question of "how many DPI can our eyes see Bruce?" which he referred to as my sending him down yet another rabbit hole).
The above assumes 20/20 vision...there are a lot of people whose vision is better or worse. The older one gets, the less close focus vision most people have (and the more people who need to wear "reading glasses"). So you milage may vary...
The above also assumes high contrast line pairs which while useful for measuring don't automatically translate directly to low contrast photographic textural detail. So, the odds are the practical limit may be a bit larger and hence the required resolution for continuous tone is prolly lower.
In general the "intended viewing distance" is said to be about the 1-1.2x the diagonal. So if you are holding an 8"x10" print in your hand, you'll prolly be holding it about 13-15 inches away from your face and be able to resolve about 286DPI. If you move it closer, you'll need more resolution as the eye can resolve more. If you move it away you need less. If your image is 30x40" the intended viewing distance is about 50" and you would need far less resolution for the print.
The downside about intended viewing distance is it assumes the viewer wants to see the entire image in their visual field...which of course is not always the case. Bruce used to say that the "intended viewing distance for a photographer was limited only by the length of their nose (or the magnifying power of their loupe)"
The next issue is the resolving capability of the medium. Even the smoothest matte papers can't resolve as much detail as glossy or semi-gloss surfaces. Beside the effect of dot "gain" you also have the issue of dot diffusion. So how much resolution you NEED for a continuous tone appearance in a print depends on the viewing distance and the nature of the media.
In general Bruce used to suggest 180PPI-480PPI depending on the viewing distance (either intended or likely) and the media.
The other question (which is of course close to my heart) is how the heck you sharpen an image for optimal printed output. That's a different subject that somebody could write a whole book on...oh, wait, we DID :~)
So,while the original author has some "interesting" ideas and suggests some "interesting" tests, I'm not at all sure his conclusions are as "interesting"...
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Thank you for that Jeff. My first thought was that sharpening was not addressed. When I first became "aware" of the subject of sharpening, it was similar to the first day I got glasses and played slow pitch softball. WOW. Move forward to the day I became aware of PK Sharpening. It was like getting tri-focals!
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It's odd that in one of the responses to a reader's comment, he says that in the real world you can't control the resolution because your file is fixed and your print size is whatever you want it to be and he doesn't recommend resampling. If that's the case, then it makes no sense to recommend to people to "test" where the sharp point is on their printers because the same "real world" limitation will come into play.
I would agree that resampling is sub-optimal and that you're better providing, say, a 259ppi file to the driver than resampling to 300 or 360 etc in most cases (in some cases, with excellent algorithms, you might see an improvement in upressing yourself). Using the likes of PK sharpener really is a better way of controlling the quality of the printed result.
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The other question (which is of course close to my heart) is how the heck you sharpen an image for optimal printed output. That's a different subject that somebody could write a whole book on...oh, wait, we DID :~)
Thanks for the post. I just finished that book, actually.
It seems to me that even if one could print a very large print at 300 dpi, when printing that large the optimal sharpening for a standard viewing distance would necessarily preclude optimal sharpening for nose-to-the-print viewing. As an inevitable tradeoff, we simply can't have it both ways. My inclination is to compromise and sharpen to the point that viewing a 40x60" print at 2 feet it is still (to steal a word) non-crunchy. I know that I definitely move to about two feet when viewing large pieces in galleries or other peoples' homes, so I've found this to be a fairly reasonable compromise.
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Thanks for the post. I just finished that book, actually.
It seems to me that even if one could print a very large print at 300 dpi, when printing that large the optimal sharpening for a standard viewing distance would necessarily preclude optimal sharpening for nose-to-the-print viewing.
Well, the viewing distance doesn't actually have anything to do with the optimal output sharpening...the only two critical factors are pixel density (PPI) and media. Viewing distance does have an indirect impact in that you choose the output resolution based on your desired output size. So, bigger printed image size would equal lower PPI which would require the sharpening for the lower pixel density.
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Well, the viewing distance doesn't actually have anything to do with the optimal output sharpening...
Hi Jeff,
I beg to differ on that. The human visual system does have a different contrast sensitivity (http://www.imatest.com/docs/sqf.html#csf) at different spatial frequencies, and those depend on viewing distance.
One could quibble on how important it is, but stating that it has nothing to do with it is just not true.
Try this (http://www.michaelbach.de/ot/fcs_SpatFreqComposites/index.html) if you still don't agree ...
Kind regards,
Bart
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The other question (which is of course close to my heart) is how the heck you sharpen an image for optimal printed output. That's a different subject that somebody could write a whole book on...oh, wait, we DID :~)
What book?
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If I may, Real World Image Sharpening by Bruce Fraser, updated by Jeff Schewe.
And a quick note about viewing distance, Gregory Crewdson produces amazing images with stunning sharpness in a format that runs to 54" x 80" (printed on an Epson 11880). He encourages viewers to study details of the image from a few inches away. It seems to me that if an image, no matter how large, has excellent sharpness at 2", it'll look good from 5 feet away as well.
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One could quibble on how important it is, but stating that it has nothing to do with it is just not true.
As it relates to the needs of image output sharpening for digital printed output, no, viewing distance is NOT a factor in image sharpening needs...(the links you cite not withstanding)
How much resolution you NEED for what size print is related directly to viewing distance and that final resolution (pixel density) IS the determining factor, along with the media type, for determining proper image sharpening for printing.
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It seems to me that if an image, no matter how large, has excellent sharpness at 2", it'll look good from 5 feet away as well.
Maybe, maybe not. Ever see Seurat's Sunday Afternoon on the island of La Grande Jatte (http://en.wikipedia.org/wiki/Sunday_Afternoon_on_the_Island_of_La_Grande_Jatte)?
The relationship between looking real close and looking at the intended viewing distance are not necessarily related. I've seen wonderful images whose prints from a distance are great that look like crap from up close...just because something may look technically good up close doesn't mean anything definitive when judged from a distance.
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I've seen wonderful images whose prints from a distance are great that look like crap from up close...
I think this is the opposite of what Randy is saying...
Ever see Seurat's Sunday Afternoon on the island of La Grande Jatte (http://en.wikipedia.org/wiki/Sunday_Afternoon_on_the_Island_of_La_Grande_Jatte)?
I'm curious what you've seen in this image that makes you bring it up?
I don't see how an image that is well-printed and holds up at close-range will somehow "fall apart" at a distance. If the subject material is too busy or some such, that may impact the aesthetics, but I'm at a loss to see how printing it differently will save the day.
I feel it's just the case that it's just *impractical* (not techically feasible) to have enough information to make every image we print, at any size, look good from 2" away. Assuming infinite data, computing/printing horsepower, and sufficiently low cost, is there any reason you wouldn't print at a very high resolution?
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If I may, Real World Image Sharpening by Bruce Fraser, updated by Jeff Schewe.
And a quick note about viewing distance, Gregory Crewdson produces amazing images with stunning sharpness in a format that runs to 54" x 80" (printed on an Epson 11880). He encourages viewers to study details of the image from a few inches away. It seems to me that if an image, no matter how large, has excellent sharpness at 2", it'll look good from 5 feet away as well.
The accuracy of the inkjet drops is not a constant nor is the acutance on the substrate.
I like Jeff's definition further down which is a perfect way of saying pixel peeping on prints has no relation to the visual appearance to your eye when distance is considered.
I suppose what could be a very good addition to printer driver sharpening algorithms is the intended viewing distance changing the unsharp mask other than just up or down ressing. Does that exist already in some of the cited plug ins or scripts like PK?
Qimage has very good sharpening, based on output size but viewing distance nor output size can change the printer driver masking>
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The accuracy of the inkjet drops is not a constant nor is the acutance on the substrate.
I like Jeff's definition further down which is a perfect way of saying pixel peeping on prints has no relation to the visual appearance to your eye when distance is considered.
I suppose what could be a very good addition to printer driver sharpening algorithms is the intended viewing distance changing the unsharp mask other than just up or down ressing. Does that exist already in some of the cited plug ins or scripts like PK?
Qimage has very good sharpening, based on output size but viewing distance nor output size can change the printer driver masking>
Neil,
Qimage at least has a flexible and transparent tool to adjust the smart sharpening. In practice with print sharpening one usually hits the limitations set by upsampling artefacts first before the other aspects like viewing distance play a role. It takes some courage to enlarge a print that the artefacts show and still keep the smart sharpening active with the excuse that the viewing distance will dissolve all the enhanced artefacts to the eye. I rather tell my customers that there wasn't enough information in the file to get a sharp blow up and do no print sharpening then. It might make the print slightly worse at viewing distance but looks more natural nearby. This has nothing to do with Qimage's algorithms, they are excellent. If there's data enough for the large print then I do not see why one wouldn't use the smart print sharpening within the viewing distance if that doesn't compromise the image quality at viewing distance.
On the article, I didn't do enough close reading to check whether aliasing on downsampling could have influenced the outcome as well. At some point you consider what you read as not very scientific and then the brain isn't involved anymore.
met vriendelijke groeten, Ernst Dinkla
Try: http://groups.yahoo.com/group/Wide_Inkjet_Printers/ (http://groups.yahoo.com/group/Wide_Inkjet_Printers/)
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Neil,
Qimage at least has a flexible and transparent tool to adjust the smart sharpening. In practice with print sharpening one usually hits the limitations set by upsampling artefacts first before the other aspects like viewing distance play a role. It takes some courage to enlarge a print that the artefacts show and still keep the smart sharpening active with the excuse that the viewing distance will dissolve all the enhanced artefacts to the eye. I rather tell my customers that there wasn't enough information in the file to get a sharp blow up and do no print sharpening then. It might make the print slightly worse at viewing distance but looks more natural nearby. This has nothing to do with Qimage's algorithms, they are excellent. If there's data enough for the large print then I do not see why one wouldn't use the smart print sharpening within the viewing distance if that doesn't compromise the image quality at viewing distance.
On the article, I didn't do enough close reading to check whether aliasing on downsampling could have influenced the outcome as well. At some point you consider what you read as not very scientific and then the brain isn't involved anymore.
met vriendelijke groeten, Ernst Dinkla
Try: http://groups.yahoo.com/group/Wide_Inkjet_Printers/ (http://groups.yahoo.com/group/Wide_Inkjet_Printers/)
Yes Ernst I know, I use it often. Yet this is adjusting the sharp level before the driver. Driver level masking is the solution that as far as I can see on inkjet printers isn't addressed. Cymbolic Science was doing something of this nature with Lightjets but masking technologies were at the time and probably are still way out of my knowledge.
Sharp handed to the printer could have toggles for variables, as I think they already with the recent Epson drivers. Yet they are not basing sharpening masks on relative viewing distances, rather assumptions at a line level.
For some reasoning behind driver screening have a look at this site:
http://www.iro.umontreal.ca/~ostrom/ (http://www.iro.umontreal.ca/~ostrom/)
A lot of the HP driver sharpening mask are coming from this>
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Driver level masking is the solution that as far as I can see on inkjet printers isn't addressed.
A lot of the HP driver sharpening mask are coming from this>
Alright, a misunderstanding. But is there still interpretation of the image possible at that stage if more images of different sizes are nested on one print page like Qimage allows? And Qimage isn't the only application that does that.
A familiar site. 90% that I do not understand but always fascinating. Referred to it when I asked whether Qimage could get an extrapolation routine for vector origin pixel images. I see that what I thought was not discovered yet for digital imaging "Cairo Tiles" is now also dicussed there. Ordered a custom made carpet with that pattern some years ago when I got fascinated with the possibilities of that pattern. I thought it had potential for CCD-CMOS sensor mosaïcs but became interested in the first place when Stork's galvano fabricated silkscreen mesh with the honeycomb structure showed the extra moiré of 3 axes symmetry. Something Cairo Tiles pattern doesn't have. Deviating here .... I will read it.
met vriendelijke groeten, Ernst Dinkla
Try: http://groups.yahoo.com/group/Wide_Inkjet_Printers/ (http://groups.yahoo.com/group/Wide_Inkjet_Printers/)
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On the article, I didn't do enough close reading to check whether aliasing on downsampling could have influenced the outcome as well. At some point you consider what you read as not very scientific and then the brain isn't involved anymore.
As far as I understand it, the question is more adressed in the comments than in the article ; basically, Ctein just says that in mixed photographic subjects (that's what his experiment is about using a 'contact print'), aliasing is far from significant, which sound rather reasonable to me (unless of course artefacts are amplified by strong sharpening? I do also regret that output sharpening is not adressed at all in the article).
If you only shoot architectural subjets (brick walls and tiled roofs), your mileage may implode.
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Co-incidentally I have been running some A4 print tests at 360 dpi on Canson Photographique 310 gsm to compare speed and print quality between my Epson 9600, Epson 7900 and HP Z3200. Using a loupe the best dithering and dot pattern to my eyes seems to be the Epson 7900 at 2880 dpi (but only just) while the worst dithering and dot pattern to my eyes is the Epson 9600 at 720 dpi. However, without the use of a loupe I can't really tell the difference when comparing dithering and dot patterns.
Edit1: Specified the three printers I compared.
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As far as I understand it, the question is more adressed in the comments than in the article ; basically, Ctein just says that in mixed photographic subjects (that's what his experiment is about using a 'contact print'), aliasing is far from significant, which sound rather reasonable to me (unless of course artefacts are amplified by strong sharpening? I do also regret that output sharpening is not adressed at all in the article).
If you only shoot architectural subjets (brick walls and tiled roofs), your mileage may implode.
Scanned film grain or what is more usual the aliased version of it in a scan. If that is what you start from it is easy to create more aliasing en route. The samples that illustrate the article did ring that bell though I didn't check it on that issue.
I have seen aliasing in more than architecture. Vegetation like grass, cane etc. Fabrics, textures.
met vriendelijke groeten, Ernst Dinkla
Try: http://groups.yahoo.com/group/Wide_Inkjet_Printers/ (http://groups.yahoo.com/group/Wide_Inkjet_Printers/)
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Co-incidentally I have been running some A4 print tests at 360 dpi on Canson Photographique 310 gsm to compare speed and print quality between three printers. Using a loupe the best dithering and dot pattern to my eyes seems to be the Epson 7900 at 2880 dpi (but only just) while the worst dithering and dot pattern to my eyes is the Epson 9600 at 720 dpi. However, without the use of a loupe I can't really tell the difference when comparing dithering and dot patterns.
The 7900 should be the best. They really worked on the masking both for the driver side and the ASIC taking advantage of 16 bit workflow too.
The substrate is of course a big factor in the acutance of the drops, hence sharpness is largely detrmined here as well.
Yet the topic seems to be going between visual appearance of sharpness distance being relative and print line shaprness at pixel peeping distances. Motifs and patterns caused by dithering are usually apparent only within very close ranges. Yet as you said on A4s this is a distance at which random patterns , motifs, etc will be within the distance to still see these artefacts.
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The 7900 should be the best. They really worked on the masking both for the driver side and the ASIC taking advantage of 16 bit workflow too.
The substrate is of course a big factor in the acutance of the drops, hence sharpness is largely detrmined here as well.
Yet the topic seems to be going between visual appearance of sharpness distance being relative and print line shaprness at pixel peeping distances. Motifs and patterns caused by dithering are usually apparent only within very close ranges. Yet as you said on A4s this is a distance at which random patterns , motifs, etc will be within the distance to still see these artefacts.
Sorry, I forgot to mention that the third printer I compared was the HP Z3200.
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Well, the viewing distance doesn't actually have anything to do with the optimal output sharpening...the only two critical factors are pixel density (PPI) and media. Viewing distance does have an indirect impact in that you choose the output resolution based on your desired output size. So, bigger printed image size would equal lower PPI which would require the sharpening for the lower pixel density.
Hi Jeff,
I beg to differ on that. The human visual system does have a different contrast sensitivity (http://www.imatest.com/docs/sqf.html#csf) at different spatial frequencies, and those depend on viewing distance.
One could quibble on how important it is, but stating that it has nothing to do with it is just not true.
Try this (http://www.michaelbach.de/ot/fcs_SpatFreqComposites/index.html) if you still don't agree ...
Kind regards,
Bart
Bart,
I'm glad to see you on LuLa. Your ImagingTechnology site is excellent, but unfortunately the forum is not that active.
Jeff's own book states (page 84), "...the secret is to keep the size of the [sharpening] halos below the threshold of visual acuity at the intended viewing distance--this is where the size of the pixels on the output becomes a critical factor"
He then goes on to say that for smaller reproductions such as used in his book (no larger than 5 x 7 inches), he tries to keep the sharpening halos to 0.01 inch, whereas for larger reproductions one can go up to 0.02 inch. If one were viewing a larger print at the same distance as for the smaller one, then it would seem as one should use the same sharpening parameters as for the smaller print. One could cut away the peripheral portion of the larger print, as it would be outside the eye's field of sharp vision in any event.
The link to Norman Koren's site regarding spatial contrast sensitivity is most appropriate for further discussion. Although the eye can resolve 60 lines per degree of arc, the frequencies around 6 cycles per degree contribute most to perceived image quality and this is the basis of the SQF measurements that Mr. Koren comments on and has incorporated into Imatest. In modern imaging using MTF, it is not sufficient to state resolution without also specifying the contrast. For example, a diffraction limited lens can resolve 200 lp/mm at the Rayleigh limit (around 10% contrast), but this contrast is too low for terrestrial imaging. Resolution at the more useful 50% contrast is only 97 lp/mm and this drops to 40 lp/mm at 80% contrast.
Just as with an aberrated camera lens, the MTF of the eye is improved by stopping down (smaller pupil size). The graph by Prof. Girod on Koren's link demonstrates that the MTF of the eye at 30 cycles per degree (60 lines/degree) is only about 17% at a pupil size of 5.8 mm but improves to around 38% at a pupil size of 2 mm. However the human visual system exhibits maximal spatial contrast sensitivity at about 6 cycles/degree.
Since the visual response is so complicated, optimal output sharpening parameters are best determined empirically, and I understand that Bruce Fraser printed thousands of images to determine the best approach, which was incorporated into PKSharpener.
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Bart,
I'm glad to see you on LuLa. Your ImagingTechnology site is excellent, but unfortunately the forum is not that active.
Jeff's own book states (page 84), "...the secret is to keep the size of the [sharpening] halos below the threshold of visual acuity at the intended viewing distance--this is where the size of the pixels on the output becomes a critical factor"
He then goes on to say that for smaller reproductions such as used in his book (no larger than 5 x 7 inches), he tries to keep the sharpening halos to 0.01 inch, whereas for larger reproductions one can go up to 0.02 inch. If one were viewing a larger print at the same distance as for the smaller one, then it would seem as one should use the same sharpening parameters as for the smaller print. One could cut away the peripheral portion of the larger print, as it would be outside the eye's field of sharp vision in any event.
The link to Norman Koren's site regarding spatial contrast sensitivity is most appropriate for further discussion. Although the eye can resolve 60 lines per degree of arc, the frequencies around 6 cycles per degree contribute most to perceived image quality and this is the basis of the SQF measurements that Mr. Koren comments on and has incorporated into Imatest. In modern imaging using MTF, it is not sufficient to state resolution without also specifying the contrast. For example, a diffraction limited lens can resolve 200 lp/mm at the Rayleigh limit (around 10% contrast), but this contrast is too low for terrestrial imaging. Resolution at the more useful 50% contrast is only 97 lp/mm and this drops to 40 lp/mm at 80% contrast.
Just as with an aberrated camera lens, the MTF of the eye is improved by stopping down (smaller pupil size). The graph by Prof. Girod on Koren's link demonstrates that the MTF of the eye at 30 cycles per degree (60 lines/degree) is only about 17% at a pupil size of 5.8 mm but improves to around 38% at a pupil size of 2 mm. However the human visual system exhibits maximal spatial contrast sensitivity at about 6 cycles/degree.
Since the visual response is so complicated, optimal output sharpening parameters are best determined empirically, and I understand that Bruce Fraser printed thousands of images to determine the best approach, which was incorporated into PKSharpener.
From that could we assume that contrast then be a combination of light brightness, and arc perception , ultimately contrast ratio without flare etc?
Local contrast and colour contrast then too , do they play into perceived sharpeness?
Interesting thread here> I am learning a lot.
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From that could we assume that contrast then be a combination of light brightness, and arc perception , ultimately contrast ratio without flare etc?
Local contrast and colour contrast then too , do they play into perceived sharpeness?
I think that is right. MTF does not address veiling flare. Some say that some Leica lens produce such good results because of low veiling flare. Color adds contrast too.
I think that scientific measurements of image quality are useful, but we have to correlate the measurements with what we actually see. Michael's discussion with Norman Koren (Imatest author) on the latest video journal was quite illuminating. Michael said that he formerly did quite a bit of testing with the DXO suite, but gave up when he saw little correlation between what he was measuring and what he was seeing in the prints. An analogous between vacuum tube audio and transistor audio was also discussed.
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Hi,
MTF is normally measured at different frequencies. I guess that low figure 5 lp/mm or 10 lp/mm actually relates to veiling flare, but I may be wrong on that:
There is an excellent discussion of MTF on Zeiss Camera Lens News.
I'd recommend downloading this image: http://www.zeiss.de/C12567A8003B8B6F/Graph...le/Image_02.jpg (http://www.zeiss.de/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild2/$File/Image_02.jpg)
And this article: http://www.smt.zeiss.com/C12567A8003B8B6F/...Kurven_2_en.pdf (http://www.smt.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/CLN_31_MTF_en/$File/CLN_MTF_Kurven_2_en.pdf)
The first image shows images with different MTF characteristics. The article discusses the MTF:s and the images.
Because the article is not easy to find I tried to collect pointers to it here: http://83.177.178.7/ekr/index.php/photoart...-and-perception (http://83.177.178.7/ekr/index.php/photoarticles/22-a-very-god-article-about-mtf-and-perception)
Best regards
Erik
I think that is right. MTF does not address veiling flare. Some say that some Leica lens produce such good results because of low veiling flare. Color adds contrast too.
I think that scientific measurements of image quality are useful, but we have to correlate the measurements with what we actually see. Michael's discussion with Norman Koren (Imatest author) on the latest video journal was quite illuminating. Michael said that he formerly did quite a bit of testing with the DXO suite, but gave up when he saw little correlation between what he was measuring and what he was seeing in the prints. An analogous between vacuum tube audio and transistor audio was also discussed.
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What this will give you is the following viewing distance and resolution required table:
Viewing Distance (inches)____ Limit (inches)______Resolution (DPI)
8 _______________________ 0.00232 ______________ 428
12 ______________________ 0.00349 ______________ 286
15 ______________________ 0.00436 ______________ 229
18 ______________________ 0.00524 ______________ 191
20 ______________________ 0.00582 ______________ 172
24 ______________________ 0.00698 ______________ 143
A couple of things related to the above...these are not my numbers but Bruce Fraser's numbers from his Real World Image Sharpening book )both the original and the one I updated). But since I'm coauthor of the current edition I stand by them (I was also the guy who asked Bruce the original question of "how many DPI can our eyes see Bruce?" which he referred to as my sending him down yet another rabbit hole).
The above assumes 20/20 vision...there are a lot of people whose vision is better or worse. The older one gets, the less close focus vision most people have (and the more people who need to wear "reading glasses"). So you milage may vary...
Wow! That's spot on, Jeff. I noticed when viewing my still images on the 65" Plasma TV, that in order to appreciate the full detail on display, I had to sit no further from the screen than 2.5 metres, which is closer than I anticipated.
I planned on positioning the Chaise Longue near the opposite wall, about 5 metres away, and under the airconditioner so that the cold blast from the airconditioner immediately above will go straight over one's head.
Now this position of 5 metres away from the screen is better for viewing substandard material, DVDs and standard resolution video as opposed to HD. But it's simply too far away for the best quality material the TV is capable of displaying, which also includes most good quality material on Blu-ray discs.
My screen is simply not big enough for the planned arrangements.
Here are my calculations based on your table. Width of TV, 56.5 inches. Total horizontal resolution 1920 dots (or RGB pixels). Therefore, DPI = 1920/56.5 = 34 dpi.
If 143 dpi is required for a viewing distance of 24", then the viewing distance for 34 dpi should be 142/34x24 = 101" which is almost precisely 2.5 metres.
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Hi,
MTF is normally measured at different frequencies. I guess that low figure 5 lp/mm or 10 lp/mm actually relates to veiling flare, but I may be wrong on that:
There is an excellent discussion of MTF on Zeiss Camera Lens News.
I'd recommend downloading this image: http://www.zeiss.de/C12567A8003B8B6F/Graph...le/Image_02.jpg (http://www.zeiss.de/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild2/$File/Image_02.jpg)
And this article: http://www.smt.zeiss.com/C12567A8003B8B6F/...Kurven_2_en.pdf (http://www.smt.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/CLN_31_MTF_en/$File/CLN_MTF_Kurven_2_en.pdf)
The first image shows images with different MTF characteristics. The article discusses the MTF:s and the images.
Because the article is not easy to find I tried to collect pointers to it here: http://83.177.178.7/ekr/index.php/photoart...-and-perception (http://83.177.178.7/ekr/index.php/photoarticles/22-a-very-god-article-about-mtf-and-perception)
Best regards
Erik
Erik,
I downloaded that article and the images after you recommended them in a previous post, but I don't see veiling glare (or flare) discussed. Part 1 (CLN_MTF_Kurven_EN.pdf) does discuss veiling glare on page 16 and I surmise that it is not measured by MTF: "MTF measurements say nothing about this macro contrast. They gauge only the correction of the lens, i.e. the small deviations of the light beams, while the macro contrast depends on the veiling glare of the lens, i.e. on the large deviations."
They do show a PSF demonstrating flare. I thought that the MTF could be derived from a Fourier transform of the PSF, so I am a bit puzzled here. It had been my impression that flare was normalized out of the MTF calculation. How do you interpret this? The articles are very good, but are somewhat dense to the layman.
Regards,
Bill
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Hi,
My reasoning is that MTF is 100% at zero lp/mm is always 1, theoretically. Veiling flare would reduce contrast, so contrast would be less then 1. As I said i was not really sure about this and your reading indicates that I was wrong. I didn't mention the articles as a proof, but wanted to share them as they give good insight in how MTF shows up in real world. I'm going to reread the articles my self.
Best regards
Erik
Erik,
I downloaded that article and the images after you recommended them in a previous post, but I don't see veiling glare (or flare) discussed. Part 1 (CLN_MTF_Kurven_EN.pdf) does discuss veiling glare on page 16 and I surmise that it is not measured by MTF: "MTF measurements say nothing about this macro contrast. They gauge only the correction of the lens, i.e. the small deviations of the light beams, while the macro contrast depends on the veiling glare of the lens, i.e. on the large deviations."
They do show a PSF demonstrating flare. I thought that the MTF could be derived from a Fourier transform of the PSF, so I am a bit puzzled here. It had been my impression that flare was normalized out of the MTF calculation. How do you interpret this? The articles are very good, but are somewhat dense to the layman.
Regards,
Bill
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I'm glad to see you on LuLa. Your ImagingTechnology site is excellent, but unfortunately the forum is not that active.
Hi Bill, I'm glad to be here. Just to make sure there is no misunderstanding, I'm not associated with Norman Koren's site (although we exchanged DSP info and other technicalities in the past). Norman has a great collection of knowledge available to all on his site, and he's a very nice person. His forum is just one method for maintaining contacts with mainly the imaging industry.
Jeff's own book states (page 84), "...the secret is to keep the size of the [sharpening] halos below the threshold of visual acuity at the intended viewing distance--this is where the size of the pixels on the output becomes a critical factor"
Yes, that's only too obvious (as long as you can't see it ...), although I'd prefer to avoid halos as much as possible in the first place. One cause for halos is repeated sharpening passes, combined with a poor resampling algorithm.
He then goes on to say that for smaller reproductions such as used in his book (no larger than 5 x 7 inches), he tries to keep the sharpening halos to 0.01 inch, whereas for larger reproductions one can go up to 0.02 inch. If one were viewing a larger print at the same distance as for the smaller one, then it would seem as one should use the same sharpening parameters as for the smaller print. One could cut away the peripheral portion of the larger print, as it would be outside the eye's field of sharp vision in any event.
I think that output sharpening should be steered by the characteristics of the output modality, not by tolerable halos as a guiding principle. The printing process (whether inkjet, photochemical, printing press, or whatever else) will add it's particular loss of detail (loss of MTF response). It's that loss that we strive to pre-compensate for. Compensating for lack of capture resolution is another subject, although in a parametrised workflow it can take place together with the final resampling and output sharpening, while avoiding cumulative artifact amplification.
The link to Norman Koren's site regarding spatial contrast sensitivity is most appropriate for further discussion. Although the eye can resolve 60 lines per degree of arc, the frequencies around 6 cycles per degree contribute most to perceived image quality and this is the basis of the SQF measurements that Mr. Koren comments on and has incorporated into Imatest. In modern imaging using MTF, it is not sufficient to state resolution without also specifying the contrast.
Exactly, and the notion of contrast sensitivity also leads to useful remedies to compensate for output losses, or even augment the shortcomings of the capture chain. In postprocessing we can manipulate the MTF of the final image around certain spatial frequencies which can result in a higher percieved resolution (without artifacts), as long as we address the correct spatial frequencies, the ones that matter. Viewing distance does matter and, although we cannot always cater for every possible scenario, we can optimize our final MTF for the most probable situations.
Just as with an aberrated camera lens, the MTF of the eye is improved by stopping down (smaller pupil size). The graph by Prof. Girod on Koren's link demonstrates that the MTF of the eye at 30 cycles per degree (60 lines/degree) is only about 17% at a pupil size of 5.8 mm but improves to around 38% at a pupil size of 2 mm. However the human visual system exhibits maximal spatial contrast sensitivity at about 6 cycles/degree.
Yes, this tells us not only that the viewing conditions matter, but also where the most impact of our postprocessing can be expected. It also tells us that sticking to a PPI centered compensation only, for sharpening losses, is somewhat problematic to say the least, because it also doesn't recognise the impact of viewing distances. BTW personally I focus on the 8 cycles/degree eye contrast criterion, also because there are people with better than average eyesight.
Since the visual response is so complicated, optimal output sharpening parameters are best determined empirically, and I understand that Bruce Fraser printed thousands of images to determine the best approach, which was incorporated into PKSharpener.
Although I don't dismiss empirical determination, I prefer to use that as a last resort. The problem with empirically derived solutions is that we can't learn about the underlying processes, and thus potentially overlook the important principles (the ones we can use to our advantage).
Cheers,
Bart
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MTF is normally measured at different frequencies. I guess that low figure 5 lp/mm or 10 lp/mm actually relates to veiling flare, but I may be wrong on that:
Hi Erik,
Veiling flare is primarily a localized phenomenon in an image, although in a mediocre lens design it can spread throughout the image. It will manifest itself near the lower spatial frequencies in the image capture, but it is only responsible for a (small) part of the (reduction of the) capture frequency response.
One should also be careful in not confusing the eye's MTF curve with the image's MTF. A peak contrast sensitivity at around 8 cycles/degree (~16 lines/degree) deals with print detail at a viewing distance of 8-10 inches of around 100 PPI.
Cheers,
Bart
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Although I don't dismiss empirical determination, I prefer to use that as a last resort. The problem with empirically derived solutions is that we can't learn about the underlying processes, and thus potentially overlook the important principles (the ones we can use to our advantage).
Empiricism and theory should go hand in hand. If there's a conflict, I'll opt for the empricism.
It's always been good advice, when preparing images for large prints, to increase local contrast dramatically. By that, I mean, using Photoshop Unsharp Mask settings at something like, 50 pixels radius setting and 30-50% amount, at the same time, of course, protecting any highlights and shadows which may be near to clipping.
This in effect increases the MTF of the very low frequencies, which is what you need when viewing images from a distance.
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Empiricism and theory should go hand in hand. If there's a conflict, I'll opt for the empricism.
It's always been good advice, when preparing images for large prints, to increase local contrast dramatically. By that, I mean, using Photoshop Unsharp Mask settings at something like, 50 pixels radius setting and 30-50% amount, at the same time, of course, protecting any highlights and shadows which may be near to clipping.
This in effect increases the MTF of the very low frequencies, which is what you need when viewing images from a distance.
Hi Ray,
This is an exellent example of where empiricism can lead people on a different path than the one they intended to go. A large radius unsharp mask does a local tonemapping operation, it changes the tonality based on local brightness. It does not necessarily change the MTF in a way that emphasizes targeted spatial frequencies. For that, one needs to apply a high pass filtered layer, e.g. in (although not perfect) Soft light blending mode, which is what theory tells us.
I'm not saying that a local tonemapping operation doesn't help images, it's just that it addresses another issue.
Cheers,
Bart
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Hi Ray,
This is an exellent example of where empiricism can lead people on a different path than the one they intended to go. A large radius unsharp mask does a local tonemapping operation, it changes the tonality based on local brightness. It does not necessarily change the MTF in a way that emphasizes targeted spatial frequencies. For that, one needs to apply a high pass filtered layer, e.g. in (although not perfect) Soft light blending mode, which is what theory tells us.
I'm not saying that a local tonemapping operation doesn't help images, it's just that it addresses another issue.
Cheers,
Bart
Bart is correct.
If the 30-50% is really pixel % then what default. Or did it really refer to pixel grid width. Then 30-50 pixels will cause a hefty shift . In that case I think you'd want to get into the habit of smart sharpening which is the way we used to sharpen when scanning. Funny how long it took to make it's way into Photoshop!
There is a lot of rage about High Pass, or high pass with a mode layer over a mid grey.
It is interesting as an effect but it sure looks like a hack to me. When printing with an enlarger without mask films, there isn't any sharpening. Still look more photographic than any high pass filter, so I am not convinced that a heavy hand is going to make a print better. Theory is one thing, but appreciation of the culture of traditional analogue imagery does not necessarily retain integrity IMO when too much of the printers hand becomes apparent.
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Hi Ray,
It does not necessarily change the MTF in a way that emphasizes targeted spatial frequencies. For that, one needs to apply a high pass filtered layer, e.g. in (although not perfect) Soft light blending mode, which is what theory tells us.
Hi Bart,
Did you forget I mentioned protecting the highlights and shadows?
I always opt for the simpler system. If you are going to increase local contrast, then it has to be local, or targeted, otherwise it's global.
The simplest way of doing this is to select with the magic wand the highlights and shadows that won't benefit from contrast enhancement, feather 2 or 3 or 5 pixels, then invert.
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Hi Bart,
Did you forget I mentioned protecting the highlights and shadows?
Hi Ray,
No I didn't, but it has nothing to do with adjusting for specific spatial frequency response. Of course one should protect shadows and highlights when applying local contrast enhancement.
I always opt for the simpler system. If you are going to increase local contrast, then it has to be local, or targeted, otherwise it's global.
The simplest way of doing this is to select with the magic wand the highlights and shadows that won't benefit from contrast enhancement, feather 2 or 3 or 5 pixels, then invert.
The Blend-If functionality in Photoshop is another efficient way of doing it, but there are many other methods possible as well.
What I am saying is that we can exploit the contrast sensitivity of the human eye, with a peak at say 8 cycles/degree, by boosting the MTF response at (and beyond) those frequencies. That has little to do with normal image contrast, it's confined to certain specific spatial frequencies and that is linked to viewing distance.
Here's a little test to illustrate:
(http://www.xs4all.nl/~bvdwolf/temp/CSF.png)
Look at that image when you walk away from your display. At different distances you'll see a maximum contrast at different particular spatial frequencies, allowing you to discriminate lower contrast detail.
Cheers,
Bart
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In general you cannot optimize a single print detail-wise for all viewing distances. If you prepare an image so it looks perfect at a few inches away (sharp, natural, no artifacts) then it might look fine much farther away, but it won't be as sharp as it could be. That is, you could sharpen the image a lot more if you knew you'd be viewing it from no closer than 10 feet away. But then that same image would look bad when viewed at 10 inches.
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Hi Ray,
No I didn't, but it has nothing to do with adjusting for specific spatial frequency response. Of course one should protect shadows and highlights when applying local contrast enhancement.
Hi Bart,
Doesn't the selection of pixel radius in the unsharp mask target the spacial frequency you want to sharpen?
For example, playing around with the following chart of really low frequencies demonstrating some very poor MTF, applying 100% sharpening with a pixel radius of 1 does nothing to increase the MTF of those frequencies. However, increasing the pixel radius to 60 produces a very dramatic improvement.
[attachment=19305:Comparison_of_3.jpg]
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Doesn't the selection of pixel radius in the unsharp mask target the spacial frequency you want to sharpen?
Hi Ray,
Yes, pixel radius does, but that's only true for the radius that is used and frequencies in that neighborhood (especially somewhat lower frequencies).
For example, playing around with the following chart of really low frequencies demonstrating some very poor MTF, applying 100% sharpening with a pixel radius of 1 does nothing to increase the MTF of those frequencies. However, increasing the pixel radius to 60 produces a very dramatic improvement.
Be careful with mixing up spatial frequencies in the image, with spatial frequencies in the MTF of our eyes. Also, the large radius sharpening works out differently on areas of different large area brightness distribution, but hardly addresses spatial frequencies (other than overall brightening/darkening) near the limiting resolution of the image.
Cheers,
Bart
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In general you cannot optimize a single print detail-wise for all viewing distances. If you prepare an image so it looks perfect at a few inches away (sharp, natural, no artifacts) then it might look fine much farther away, but it won't be as sharp as it could be. That is, you could sharpen the image a lot more if you knew you'd be viewing it from no closer than 10 feet away. But then that same image would look bad when viewed at 10 inches.
Eric (and Bart),
For discussion, let's assume that we want to sharpen for a viewing distance of 34 cm (13.5 inches), to coincide with the conditions given by Bob Atkins in his discussion of SQF (http://bobatkins.com/photography/technical/mtf/mtf4.html). The eye can resolve down to 30 cycles/degree (60 lines or 30 line pairs per degree), but is most sensitive as far as apparent sharpness is concerned to about 6 cycles/degree. At a viewing distance of 34 cm, these frequencies correspond to 1 cycle/mm and 5 cy/mm respectively. 5 cy/mm is 127 cy/inch or 254 lines/inch and is in agreement with Jeff Schewe's figures.
To sharpen for the optimal MTF of the eye at this viewing distance would seem to require parameters that optimize the image at 1 cy/mm. How do we accomplish this? Jeff would set the sharpening radius to to keep the sharpening halos to about 0.01 inch, but does not take the viewing distance into account. How does this correspond to the supposed ideal sharpening for this image?
It is interesting to note that for a full frame 35mm camera, the image on the sensor must be enlarged 8 times to get an 8 x 12 inch print, so the required resolution in the plane of the sensor to obtain the above resolutions would be 8 cy/mm and 40 cy/mm respectively and that these resolutions correspond to the 10 cy/mm and 40 cy/mm often given for MTF for 35 mm lens testing.
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Am I the only one who is failing to completely understand this thread?
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Am I the only one who is failing to completely understand this thread?
No, I do not grasp all of it either.
But based on what I have seen of Bart's messages in the past, I very much trust his knowledge.
Then there is that aspect of how to translate the theory reasonably efficient to daily practice.
Using Qimage here with Z3100 and Z3200 printers and always making proof strips for the larger sizes before the actual print is made.
With the knowledge that it seldom happens that there is plenty of image data at that size.
met vriendelijke groeten, Ernst Dinkla
Try: http://groups.yahoo.com/group/Wide_Inkjet_Printers/ (http://groups.yahoo.com/group/Wide_Inkjet_Printers/)
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In general you cannot optimize a single print detail-wise for all viewing distances. If you prepare an image so it looks perfect at a few inches away (sharp, natural, no artifacts) then it might look fine much farther away, but it won't be as sharp as it could be. That is, you could sharpen the image a lot more if you knew you'd be viewing it from no closer than 10 feet away. But then that same image would look bad when viewed at 10 inches.
Hi Eric,
Obviously one cannot optimize for all conceivable viewing distances at the same time. Obviously one would like to optimize for a given viewing distance, because it is relatively easy to do (once one considers the Contrast Sensitivity limitations of human vision).
Does that mean that we cannot do anything, even with our knowledge of the CSF (http://D:\Users\Bart\Documents\Reference\CSF\Contrast%20Sensitivity%20Function1.htm)? IMHO the easy answer is not the correct answer, and I hope to demonstrate it with the following (sharpened) adaptation of the image I posted before:
(http://www.xs4all.nl/~bvdwolf/temp/CSF_IPMR.png)
Same test as earlier/above, but when you now increase the viewing distance to the screen, you'll see that the low contrast high spatial frequency detail stays visible much longer, arguably even at almost the same level as larger detail, untill one exceeds the critical viewing distance far enough. The explanation is that the image has received a "multi-resolution" sharpening. The MR-sharpening effectively consisted of an increasing level of sharpening as the spatial frequencies got higher.
That resulted in an increased amplitude of the higher frequencies as illustrated by this horizontal cross section plot of amplitude:
(http://www.xs4all.nl/~bvdwolf/temp/CSF_IPMR_Plot.png)
Is the sharpening perfect? No, there are artifacts visible. Part of the problem lies in the fact that the original detail was already partially aliased, and that was only brought out better by sharpening. BTW that is also why it important to print at the native resolution of one's printer (driver) usually 600 or 720 PPI, and sharpen at that final PPI level. The Shannon/Nyquist theorem states that we require more than 2 lines to reliably samle a single line. Sharpening in general will make aliasing visible, but at these high PPI levels the aliases will be less present/visible. I know that some participants of this forum are of an opinion that there is no benefit to be expected from upsampling to the native PPI (which can vary with paper choice) of the printer, but I obviously don't agree.
Another part of the problem is that we are looking at a computer screen with very poor (usually 96 PPI) resolution, so even the finest detail is very easily resolved by our eyes. The target itself of course also presents a worse case torture test, and I exaggerated the amount of sharpening to drive the concept home, and we can also expect larger losses due to the print process than by viewing a display. Doing it in a more subtle way could be used for web publishing, but then we also have to consider a usually predictable close viewing distance, which reduces the need for a multi-resolution approach.
I hope this demonstration will open the eyes of some of those who tend to debate from an entrenched position. The glass is half full, there are more possibilities than are currently being used.
Cheers,
Bart
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Obviously one cannot optimize for all conceivable viewing distances at the same time. Obviously one would like to optimize for a given viewing distance, because it is relatively easy to do (once one considers the Contrast Sensitivity limitations of human vision).
The fact is, photographers tend to want their prints to look good from any distance. That's presumably why some photographers spend tens of thousands of dollars on a 60mp MFDB.
The photograph is different from a painting in respect that the large painting really needs to be viewed from a good distance to be apreciated, especially impressionistic paintings.
Any photographic print, however large, will invite the photographer to inspect it from a close distance to see the resolution.
In the real world, the closer you get to any subject, the more detail you see. If your eyesight's not good enough at close distances, wear spectacles and you'll see more detail. Peer through a microscope and you'll see even more detail.
The photograph attempts to capture reality, or at least the reality we saw from the position we were when we took the shot. There's a certain fascination in being able to see more detail the closer you get, just as in the real world.
In fact, in the real world you may never get close enough to see the veins in the eyeball of your favourite movie star. A photograph may capture such detail so you can get close enough.
An impressionistic painting from close up, tends to look like crap, just a jumble of brush strokes. Likewise, a large advertising poster from across the highway might look terrific from a distance of 30 metres. Inspect it close up, and all you see are colored dots the size of small peas.
Perhaps the significant question here is, having optimised a print for viewing at a large distance, is it also possible to make it presentable at a close viewing distance without compromising those qualities appreciated at the larger distance.
Bart implies that it is, but I'd like to see some real-world photos demonstrating this. My feeling is that the exaggerated contrast of the print that makes it suitable for distance viewing, will tend to look like crap at close distances.
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I agree with Ray: there is a fascination in photography of so much sharp detail that the closer you get the more you can see - that is a difference with most painting (or TV and video). Balancing out all the wonderful detail with the question of contrast and the overall general beauty of a print from various viewing distances can not be reduced to a single formula for everyone - each photographer has to figure what works for their particular imagery and taste. Just like in selecting which type of paper to use, which type of camera system - and for some (like me) ultimate sharpness is not even desired. (though I did generally work with large format view cameras for much of my work)
Howard
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The Multi-Resolution Sharpening Bart mentions, is this the same as the Adaptive Unsharp plug-in? I did a brief web search on Adaptive Unsharp and it sounds like they might be the same.
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The Multi-Resolution Sharpening Bart mentions, is this the same as the Adaptive Unsharp plug-in? I did a brief web search on Adaptive Unsharp and it sounds like they might be the same.
Hi Deepsouth,
I don't know what that plugin does, but I assume it doesn't sharpen smooth areas such as the sky, a sort of built-in masking.
The functionality I'm mentioning targets multiple resolution levels in a given image at the same time. I'm working on a special approach, but for the example I used a special sharpening function of a program for astronomical image processing called ImagesPlus in a novel (viewing distance compensating) way. Maybe I should patent it ...
When I can find a little time, I'll prepare an image crop that has been processed this way and make it available for either display or print purposes. That way people can try it themselves on their printer. One of the issues is that different printers deteriorate the image in different ways, so I'll have to figure out something that on average still works okay.
Cheers,
Bart
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When I can find a little time, I'll prepare an image crop that has been processed this way and make it available for either display or print purposes. That way people can try it themselves on their printer. One of the issues is that different printers deteriorate the image in different ways, so I'll have to figure out something that on average still works okay.
Cheers,
Bart
Bart,
I wonder how significant this issue is. If anyone wants an image to look good from both afar and close up, then the first requirement is to get a camera with a high pixel count. In fact, the P65+ is the current ideal candidate.
With such a DB, I imagine one could produce a 36" x 48" print which looks as great as a print from a humble 12.7mp 5D, viewed from a distance of, say 3 metres. But, on close inspection the P65 print will exhibit far more detail.
If one considers the print as a work of art, like a painting, the fact that it also looks good at a closer distance than one would view the print to appreciate the work as a composition, is a sort of bonus, but perhaps not the main point.
Nevertheless, if one can tinker with sharpening routines so that the result from both afar and close up is not compromised, then that's ideal.
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The functionality I'm mentioning targets multiple resolution levels in a given image at the same time. I'm working on a special approach, but for the example I used a special sharpening function of a program for astronomical image processing called ImagesPlus in a novel (viewing distance compensating) way. Maybe I should patent it ...
Cheers,
Bart
Bart,
Like your comments on anti-aliasing routines improved Qimage's downsampling some years ago this could improve Qimage on smart print sharpening features. I wouldn't mind if that means a Qimage "Extreme" Studio version for an extra 10$. It is possible that the big money is at the other side, several representatives of that side on this forum :-)
met vriendelijke groeten, Ernst Dinkla
Try: http://groups.yahoo.com/group/Wide_Inkjet_Printers/ (http://groups.yahoo.com/group/Wide_Inkjet_Printers/)