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Author Topic: Sensor & Sensibility II  (Read 14968 times)
DiaAzul
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« Reply #40 on: August 27, 2006, 11:05:20 AM »
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But this would thus result in a clear and obvious sample of better performance of larger-pixel-bin sensors vs smaller-pixel-bin. That is, at the current state of affairs. I completely agree with you that the performance of smaller-pixel-bins can and will increase.

As a matter of fact, eventually the larger-pixel-bin advantage may for example be countered by speed advantages of reading smaller-pixel-bins. I'm purely speculating here, but I recall research about taking multiple exposures in a single exposure. Eventually the read-out speed may make this viable for smaller-pixel-bins, but larger pixel-bins simply don't "fill up" quick enough, their "native" iso being to high?

[a href=\"index.php?act=findpost&pid=74635\"][{POST_SNAPBACK}][/a]

This all comes back to a trade off and choice if which camera is most appropriate for your needs. Is it really necessary to have a really high dynamic range sensor if what you need is resolution and you are typcially shooting low contrast scenes? There are definite advantages to higher dynamic range sensors from a preservation of colour and tonality information prior to applicaton of a tonal curve. However, if you can tolerate some clipping of channels, then for most images it could be argued that the 5D is over engineered for the task and that pixels one half or quarter the size with higher density/resolution would be better - the Nikon route for instance.

There is another aspect that comes into play - john points out that the 5D/20D dynamic range converges from 200ISO upwards. This is indicative that the limitation on dynamic range is not generated as a result of the size of the pixel, but perhaps by other sources of noise in the line amplifiers, analogue to digital converters. We may need to see improvements in the support electronics around the sensor before we see any difference in performance between small and large pixels (i.e. pixel size is not the only limitation to image quality)

There has been prior discussion on alternative strategies for reading information from pixels - non linear response characteristics, refresh when full and reading multiple times during the exposure. All are technically feasible but generally introduce other problems and sources of noise which limit their usefulness. In the case of multiple samples over the course of one exposure, the main problem would be one of high clock speeds required to achieve enough samples (and higher clock speeds generate more on chip noise, higher power consumption and more heat) and also allowing sufficient time for the pixels to reset 3-5mSec during each sampling period (ie. you loose 3-5mSec of data each sample and you would severely limit the maximum effective shutter speed that could be used). The next most likely innovation is  an improved version of the foveon sensor with full colour read out per pixel - but we shall see what turns up over the next couple of months.
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« Reply #41 on: August 27, 2006, 12:04:35 PM »
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speed that could be used). The next most likely innovation is  an improved version of the foveon sensor with full colour read out per pixel - but we shall see what turns up over the next couple of months.

I would love to see a hybrid design:

A bayer sensor with two layer read out (instead of 3 as in foveon sensor), and a yellow-cyan checker board pattern to capture a full channel of green, and two checkerboard channels of red and blue. "Debayering" a checkerboard pattern is fairly easy and requires far less channel-cross-over data. The latter will be used anyway to accommodate other aspects of the image processing (like noise reduction), so I think that would be the perfect balance between the high bit advantage of a single layer vs the image integrity of capturing 3 colors.
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Oscar Rysdyk
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« Reply #42 on: August 27, 2006, 02:20:21 PM »
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I would love to see a hybrid design:

A bayer sensor with two layer read out (instead of 3 as in foveon sensor), and a yellow-cyan checker board pattern to capture a full channel of green, and two checkerboard channels of red and blue. "Debayering" a checkerboard pattern is fairly easy and requires far less channel-cross-over data. The latter will be used anyway to accommodate other aspects of the image processing (like noise reduction), so I think that would be the perfect balance between the high bit advantage of a single layer vs the image integrity of capturing 3 colors.
[a href=\"index.php?act=findpost&pid=74654\"][{POST_SNAPBACK}][/a]

Interesting theory, however, I am not sure how you are trying to get any advantage out of what you are suggesting. The foveon sensor is based upon the principle that different wavelengths of light are absorbed at different depths within the semiconductor and relies upon a 'stacked' set of sensors of different thickness to capture the light within a particular pass band. In a bayered sensor elecron-hole recombination takes place at particular depth within the semiconductor and varies by colour. There is nothing particular efficient about the bayer design when it comes to light gathering capability. Putting a yellow-cyan filter in front of a foveon sensor and then debayering the result would add complications - each alternate pixel would have to be of a different design i.e. a green-blue pixel would be different design from a green-red pixel and you would be filtering out light that could reasonably be captured and extracted for the final image.

Two things stand out with foveon type designs:

They should be more efficient long term compared with a bayer type sensor assuming that the fill factor can be increased to a comparable level. The issue here is not light capture, but creating a capacitor for each of the three layers within the same space as the one capacitor for a bayer device.

It may be possible to go more creative and have a four/five/six layer sensor e.g Infra-Red, Red, Green, Blue, UV for those that want more capability in their conversion to black and white.
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Ray
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« Reply #43 on: August 28, 2006, 03:21:34 AM »
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I'm all for the underdog. Speaking of which: could you repost DPP conversions of the same files? (or post the RAW).

Oscar,
I haven't got DPP installed on this computer. I don't use it. Also, I don't know how to send you the RAW images. I'm on a dial-up 56kb connection.

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It seems the 20D is outresolving the lens by a fair amount, any way we can change that?

As far as I know, all my lenses are sharpest at f8. Some are possibly equally sharp at f5.6. I took a few comparison shots today of the same target but using the TSE-90mm, probably my sharpest lens excluding the Canon 50/1.8 ll. Having taken a brief look at some of the images, some of which were taken at a different distance such that equal FoV crops from both cameras contain an equal number of pixels, I find no resolution advantage for the 20D with the better lens.

This notion of some DSLR sensors outresolving lenses seems very exaggerated to me. The only time I ever get a clear indication the 20D sensor is outresolving the lens is when I stop down to f16 or lower, or stop up to full aperture or close to, or compare corner resolution with centre resolution. The 5D has the advantage of delivering (outside of extreme pixel peeping) virtually equal resolution at f16 as at f8, with my lenses anyway.

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What could be the source of the rather significant chromatic aberration in the 20D file?

No idea! But the word birefringence springs to mind  .

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I know, but that was not the question. The question is: why does the industry want 1200dpi to 2400dpi for text and line-art?

I don't know, Oscar. You tell me   . I could offer a few guesses. Because the technology is now available; why not use it? Because it delivers an almost imperceptible additional crispness to the text? Because it looks very good to extremely shortsighted readers or readers who use high powered reading glasses or simply a magnifying glass?

I think you are evading the issue which started this diversion, which is, a 5.5" wide 400% crop of a 5D image on a 1280x1024 monitor is representative of a 10ftx15ft print of the whole image. It's true that there will be jagged edges visible on the monitor as a result of the uninterpolated 96 dpi monitor resolution, but these will tend to disappear when the file is uprezzed  for printing, and of course they will also disappear on the monitor when viewing the 400% file after uprezzing, as in the examples below of previously posted 400% crops which have now been uprezzed to 240 dpi with GF and displayed at 40% enlargement on the screen.

I suppose one could now say, the images below are more representative of a 10ftx15ft print of the entire image, because this is now a small part of the file I would send to the printer, although it's still not sharpened and processed in any other way. So it's still not yet fully and truly representative of the 10ftx15ft print. Agreed?

[attachment=931:attachment]
« Last Edit: August 28, 2006, 03:29:26 AM by Ray » Logged
Ray
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« Reply #44 on: August 28, 2006, 03:59:37 AM »
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I should mention, for the benefit of those who own both a 5D and 20D and who might want to compare images at the pixel level without interpolation, my initial calculation of 1.265x the distance to target for the 20D proved to be slightly out. It was necessary to bring the tripod and camera back a further inch or two. Having done that, all crops contained close to exactly the same number of pixels. But I was curious as to why my calculations were not exact, so I went back to the basic information about these sensors, on dpreview. First, the 5D sensor is not 36mmx24mm but 35.8x23.9mm. Secondly, and most significantly, the 20D has 8.2 effective megapixels. I'd used a figure of 8mp in my calculations.

My initial calculation was 1.265x. A more accurate multiplier is 1.275. Just for the record   .
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opgr
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« Reply #45 on: August 28, 2006, 04:30:50 AM »
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As far as I know, all my lenses are sharpest at f8. Some are possibly equally sharp at f5.6. I took a few comparison shots today of the same target but using the TSE-90mm, probably my sharpest lens excluding the Canon 50/1.8 ll.
Okay, a 50/1.8 is definitely fine for the 20D, so that is not the problem. But the 20D image is far more blurry than is to be expected. Simple focussing differences?

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I don't know, Oscar. You tell me   . I could offer a few guesses. Because the technology is now available; why not use it? Because it delivers an almost imperceptible additional crispness to the text? Because it looks very good to extremely shortsighted readers or readers who use high powered reading glasses or simply a magnifying glass?
You're kidding me, right?
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Oscar Rysdyk
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« Reply #46 on: August 28, 2006, 04:48:36 AM »
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You're kidding me, right?
[a href=\"index.php?act=findpost&pid=74715\"][{POST_SNAPBACK}][/a]

No I'm not. I thought commercial printers (as opposed to giclee printers) used 150 dpi for all purposes. I'm not involved in the printing profession. I'm a mere amateur.

I rely upon people like you to advise upon and explain such matters   .
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« Reply #47 on: August 28, 2006, 05:28:35 AM »
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It can also be the 5D's coarser pixel pitch.

After digesting all the information I have come to the conclusion that this may be the core of the issue. Here's my thinking:

Supposed advantages of larger pixelbins:

1) more dynamic range,

2) less noise,

3) better per pixel contrast.


1) more dynamic range
From everything we know this is only marginally true. Using a middle-gray exposure it may be somewhat relevant but certainly not earth-shattering. For a correct ETTR highlights exposure, the difference obviously resides in the darktones where it becomes obscured in a discussion about how much noise is acceptable.
Apparently the difference becomes smaller at higher iso.
For an 8mpx to 10mpx jump it is completely irrelevant.

 2) less noise
While true, the benefits are not immediately obvious, and can possibly be harvested only through higher bit A/D conversions. For 5D vs other brands, I believe there are too many design difference for meaningful comparison. For 5D vs 20D comparison, the 5D high iso performance is remarkable and the size of the 20D sensor components may result in more secondary irregularities such as stuck pixels. For an 8mpx to 10mpx jump, it is irrelevant.

3) better per pixel contrast
Seems certainly a decisive factor, especially in a 5D vs 20D comparison. If it is the source of the fringing, then it would certainly account for part of the subjective, easy-on-the-eyes, butter-smooth images from a 5D vs a 20D. However, for an 8mpx to 10mpx jump, it is hardly relevant.


All-in-all, I think that the smaller components in an APS-C sensor vs a FF sensor do create some system/design specific problems that are compensated for in data processing, but for an 8mpx to 10mpx jump I think that none of the advantages is remotely significant. Far more significant seem the additional components such as the AA & IR filters and microlenses.
Obviously, even more significant are the interchangeable lenses and Photographic technique used. In that respect it remains a kind of ironic paradox for an entry-level designed camera to out-resolve the more affordable lenses.

I believe that one of the reasons so many heated discussions exist on this subject is that there may be a relevant difference in large pixel-bin and small pixel-bin sensors, but these are compensated for in data processing. So, the net result is that images do not contain the usual visible noise differences that people look for, nor do the technical graphs show any significant differences.

But I believe that people certainly can experience the differences between an image on the very limit of reasonable processing vs an image that is butter-smooth from the capture stage. Whether that difference truly translates to the expenses required, remains debatable. I personally think it doesn't, not in the least because of the decreasing quality in image reproduction of the past 15 years.

A 1-series with 26mpx will NOT produce those butter-smooth pixels within the next 3 years, but the resulting images will most certainly be accepted as the quality point of reference for the industry.

Even so, I would still consider purchasing a 5D if I can afford it. Not because my photographic skills justify it, not because my imaging needs require it. But there is something magical about butter-smooth pixels which then result in buttersmooth but extremely sharp images, which is simply irresistible.
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Oscar Rysdyk
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Ray
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« Reply #48 on: August 28, 2006, 07:01:39 AM »
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Even so, I would still consider purchasing a 5D if I can afford it. Not because my photographic skills justify it, not because my imaging needs require it. But there is something magical about butter-smooth pixels which then result in buttersmooth but extremely sharp images, which is simply irresistible.
[a href=\"index.php?act=findpost&pid=74723\"][{POST_SNAPBACK}][/a]

Buttersmooth? What are you talking about, Oscar? One can always create a buttersmooth effect with a bit a gausian blur. Buttersmooth and sharp? That's an oxymoron, old chap.
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« Reply #49 on: August 28, 2006, 07:09:50 AM »
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Buttersmooth? What are you talking about, Oscar? One can always create a buttersmooth effect with a bit a gausian blur. Buttersmooth and sharp? That's an oxymoron, old chap.
[a href=\"index.php?act=findpost&pid=74729\"][{POST_SNAPBACK}][/a]

LOL... but that's exactly what a 5D is; an oxymoron amongst digital cameras. It's neither a professional, weather-sealed 1-series, nor is it an affordable, middle-league APS-C.
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« Reply #50 on: August 28, 2006, 11:19:19 AM »
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LOL... but that's exactly what a 5D is; an oxymoron amongst digital cameras. It's neither a professional, weather-sealed 1-series, nor is it an affordable, middle-league APS-C.
[a href=\"index.php?act=findpost&pid=74732\"][{POST_SNAPBACK}][/a]


Sounds like the best of both worlds to me.  

For what they are worth, below are a couple of uninterpolated 100% crops of the 5D and 20D, both using the TS-E 90mm at f8, 1/6th sec exposure and ISO 100, at adjusted distances to get an equal number of pixels in each crop.

There are slight differences, but nothing particularly significant to my eyes. The images are unsharpened and unprocessed as before with same settings in ACR regarding shadows, EC and contrast. The 5D image looks slightly contrastier.

[attachment=932:attachment]  [attachment=933:attachment]
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« Reply #51 on: August 28, 2006, 05:13:04 PM »
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No I'm not. I thought commercial printers (as opposed to giclee printers) used 150 dpi for all purposes. I'm not involved in the printing profession. I'm a mere amateur.

I rely upon people like you to advise upon and explain such matters   .
150 dpi for high contrast material such as black text on a white background is way too low.

300 dpi was considered acceptable twenty years ago.

600 dpi is nice.

1200 dpi is lovely, but can be hard to distinguish from 600 dpi without close examination.

2400 dpi is unnecessary for that purpose.  

Well, that's just my opinion, and of course you'll find differing opinions, but it's mostly quibbling.

2400 dpi in black/white is, however, quite necessary for creating rasters to emulate really smooth grey tones.

I think that when Oscar mentions the text and line art resolution for "the printing industry", he's also including grey scale rasters.

This plays back to previous discussions regarding the validity of DPReview's resolution tests for line pairs, and IIRC, the consensus was that high-contrast images and high apparent resolution go hand in hand.
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« Reply #52 on: August 28, 2006, 07:31:56 PM »
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150 dpi for high contrast material such as black text on a white background is way too low.

300 dpi was considered acceptable twenty years ago.

600 dpi is nice.

1200 dpi is lovely, but can be hard to distinguish from 600 dpi without close examination.

2400 dpi is unnecessary for that purpose. 

Well, that's just my opinion, and of course you'll find differing opinions, but it's mostly quibbling.

2400 dpi in black/white is, however, quite necessary for creating rasters to emulate really smooth grey tones.

I think that when Oscar mentions the text and line art resolution for "the printing industry", he's also including grey scale rasters.

This plays back to previous discussions regarding the validity of DPReview's resolution tests for line pairs, and IIRC, the consensus was that high-contrast images and high apparent resolution go hand in hand.
[{POST_SNAPBACK}][/a]

In this context, it is important to distinguish between pixels and halftone dots such as in Postscript. In the latter case, a halftone dot may be represented by a 16 by 16 raster pattern so that 256 levels can be represented. In this case one pixel would contain 16*16 dots.

[a href=\"http://www.ps.missouri.edu/ps2/support/TutorialFolder/ScanningTutorial/ScanningTutorial.html]http://www.ps.missouri.edu/ps2/support/Tut...ngTutorial.html[/url]
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Ray
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« Reply #53 on: August 28, 2006, 07:46:51 PM »
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150 dpi for high contrast material such as black text on a white background is way too low.

[a href=\"index.php?act=findpost&pid=74782\"][{POST_SNAPBACK}][/a]

Actually, I realise now that I'm using the wrong terminology. Offset printers and the like provide 150 lines per inch (lpi not dpi) and usually require an image ppi of twice that.

I fail to see why high image resolutions of 1200ppi and 2400ppi would serve any purpose outside of this 'apparent' characteristic of commercial printers to require double the resolution in the file.

I mean, how do these high resolutions equate to the accepted wisdom that the human eye cannot distinguish finer detail than 6.7 lp/mm on the printed page? That's 167 line pairs per inch or 335 ppi. Call it 360 ppi if you like.

I was not aware that either line art or text in my images would require an image file resolution of greater than 360 ppi.
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« Reply #54 on: August 29, 2006, 12:21:15 AM »
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I mean, how do these high resolutions equate to the accepted wisdom that the human eye cannot distinguish finer detail than 6.7 lp/mm on the printed page? That's 167 line pairs per inch or 335 ppi. Call it 360 ppi if you like.


Because there is a fundamental difference between pattern recognition and sharp focus, you can easily discern a hairline in print which may represent 1/1200th of an inch. Additionally to create such a pattern, you would have to overcome dot-gain which means the black lines in the line pairs have to be slightly smaller than the white spacing. How can you make slightly smaller lines in a regular grid? Only if the lines are comprised of even smaller dots, and a lot of them i might add...
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« Reply #55 on: August 29, 2006, 12:22:58 AM »
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Sounds like the best of both worlds to me.   

For what they are worth, below are a couple of uninterpolated 100% crops of the 5D and 20D, both using the TS-E 90mm at f8, 1/6th sec exposure and ISO 100, at adjusted distances to get an equal number of pixels in each crop.

There are slight differences, but nothing particularly significant to my eyes. The images are unsharpened and unprocessed as before with same settings in ACR regarding shadows, EC and contrast. The 5D image looks slightly contrastier.

[attachment=932:attachment]  [attachment=933:attachment]
[a href=\"index.php?act=findpost&pid=74755\"][{POST_SNAPBACK}][/a]

Interesting, something is blurring the 20d image. It's visible at normal size. See the text in the lower-right corner. While larger in the 20d image, it's readable in the 5d image.

If this is solely due to the AA filter, then it again begs the question: does the new 400D have the new filter? Given that the 5d earned its nickname (5-Dust) purportedly because of the new filter, and given that the 400D has dust-busting technology build in, I would speculate it does.

Of course, it could also be a resolving issue again or a combination.

Additionally, the 5d image shows no highlight aberrations, while it does preserve shadow transparency really well. See the left background for example which is flattened in the 20D image, and the coin stand in the 5d image renders just beautifully. This leads me to believe that the higher dynamic range is real and visible. I suppose both images were shot at iso 100?


As for line-art and text:
If you use low-resolution and anti-aliasing (if that were possible in print), then you would get tired real soon reading a page. The text looks smudged, appears to float, and you will continuously try to refocus your eyes.
So you have to create sharp type-setting without staircasing which, depending on the printing process, requires 1200dpi to 2000dpi. Your average laser print obviously requires less resolution than a quality offset print on glossy paper.

Of course, our perception processes text and line-art differently from images. Irregularities are more easily perceived and distracting, which is why the seemingly excessive text resolution requirement is as high as it is, and which is why you can't use raster for anti-aliasing.

But in my opinion the same processes are at play in image viewing. Given enough slight aberrations, no matter how small pixel wise, it will generate the same type of viewing experiences as anti-aliased text. If you try to overcome the aberrations by sharpening, it has the tendency to create irregularities in the image, exactly as it would in text or line-art.
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« Reply #56 on: August 29, 2006, 06:50:47 AM »
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Because there is a fundamental difference between pattern recognition and sharp focus, you can easily discern a hairline in print which may represent 1/1200th of an inch. Additionally to create such a pattern, you would have to overcome dot-gain which means the black lines in the line pairs have to be slightly smaller than the white spacing. How can you make slightly smaller lines in a regular grid? Only if the lines are comprised of even smaller dots, and a lot of them i might add...
[a href=\"index.php?act=findpost&pid=74817\"][{POST_SNAPBACK}][/a]

Oscar,
I still don't understand. A line 1/200th of an inch wide can be represented by a resolution of 100 line pairs per inch or 4 lp/mm. To print 4 lp/mm (100 lp/i) on an 8x12" print, it seems that an image file resolution of 240 ppi is sufficient, that is, 2.4 pixels for each line pair, or 1.2 pixels for each line.

Dot gain might often be a problem, but surely less of a problem with high quality, glossy paper, which you need to use for high resolution work. I'm not sure how small a dot a picolitre of ink produces on glossy paper, after it has spread out, but I imagine a lot smaller than the eye can see. I've read that a 6 picolitre droplet results in a 45 micron dot about half the width of a human hair. Don't know if that's true. Have you got any specific and accurate information on this issue?

I understand that commercial printers are a different ball game. Different file sizes may be required for different printing processes, but on this site we're mainly concerned with desktop printing and inkjet (or bubble jet) technology where we often have 2 or more shades of gray, 2 shades each of magenta and cyan and 4 picolitre (or smaller) ink droplets, aren't we?
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« Reply #57 on: August 29, 2006, 07:39:15 AM »
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Additionally, the 5d image shows no highlight aberrations, while it does preserve shadow transparency really well. See the left background for example which is flattened in the 20D image, and the coin stand in the 5d image renders just beautifully. This leads me to believe that the higher dynamic range is real and visible. I suppose both images were shot at iso 100?

Oscar,
Both images were shot at ISO 100. I have to agree that in general the 5D image is superior in lots of subtle ways, but there's still a question as to how significant these differences are, after skillful processing in PS (not something I consider myself an expert on).

Getting back to the whole-image print size that these 100% crops represent, I calculate that the 20D image, at my monitor resolution of 96 dpi, which would later be interpolated to 240 dpi for an Epson printer if I wanted to print it, would produce a 37.2"x24.8" print and the 5D whole image a 45.5"x30.3" print.

Since this new thread was started in order to examine real world implications of different sensor sizes, I really believe that the significance of these differences ultimately should relate to specific print sizes, but that would take a lot of time, ink and paper and I'm now preparing for my next photographic trip to SE Asia.
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« Reply #58 on: August 29, 2006, 08:35:35 AM »
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Oscar,
I still don't understand. A line 1/200th of an inch wide can be represented by a resolution of 100 line pairs per inch or 4 lp/mm.

the denominator reads 1200 (twelve hundred)...

try this with your own printer:

1) create a 1440 x 1440 pixel image.
2) make a hairline cross (1 pixel wide line, both horizontal & vertical)
3) print the file at 1x1 inch.


4) Now duplicate the layer and set blend mode to multiply
5) offset the new layer 2 pixels in both horizontal and vertical directions so that a single pixel wide gap results
6) print the file again

See if the print shows two distinct lines almost touching (you may use a loupe at this stage)
if not, nudge 1 more pixel print again until you do.

You'll then know approximately how wide your printer is printing the line, and you'll also be convinced that you can see a lot more than 1/360th of an inch... Note also that the second print shows a clearly darker plus than the first.
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Oscar Rysdyk
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« Reply #59 on: August 29, 2006, 08:49:14 AM »
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the denominator reads 1200 (twelve hundred)...
[a href=\"index.php?act=findpost&pid=74840\"][{POST_SNAPBACK}][/a]

Oops! Just goes to show that sometimes what we think we see is influenced by pre-conceptions, or maybe I just need better spectacles   .

Interesting! Unfortunately, I haven't got time to try these experiments right now. I'll have to leave it for another day.

Cheers!
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