f-stop limits for full sensor resolution

[bjanes]

Well, first, I'm not persuaded by the practical benefits of matching camera performance with 'normal' print size. I want the maximum quality I can get on the basis that too much quality for a small print is really no problem but too little quality for a large print definitely is a problem.

I adopt the same approach when scanning film. I'm not interested in scanning a slide at a low resolution suitable say for a postcard size print, in order to save time and storage, whilst putting myself in the position of having to rescan the slide if I or someone else wants a larger print at a later date.

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Ray,

Now you are talking like Nathan Myhrvold: he wants the best quality his camera is capable of achieving, not merely that need for good results at a given image size. In general, I think that is a good approach. Generally, a capture that produces an excellent large print will also do well at smaller print sizes, but as the SQF discussion by [a href=\"http://bobatkins.com/photography/technical/mtf/mtf4.html]Bob Atkins[/url] shows, this is not always the case.

Bill

[bjanes]

Your SQF graphs seem a bit puzzling. If I'm reading them correctly, they seem to be saying:

(1) The unprocessed 400D image has a higher SQF at all print sizes than the same image sharpened.

(2) The 400D image, whether sharpened or not, has a higher SQF than the sharpened Sigma 10D image, at all print sizes, but the Sigma sharpened image has a higher SQF than its unsharpened version, which is what one would expect.

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Ray,

It is not unusual for the unprocessed image to have a higher SQF than the sharpened image because of the application of standardized sharpening. For over sharpened images, Imatest tries to undo the sharpening and then apply a normal amount of sharpening.

DPReivew and many other test sites use in camera JPEGs with camera defaults and the resulting images may be over sharpened. Over sharpening is more common with P&S and is less common with SLRs where sharpening may be left to the more sophisticated user.

For an example of an over sharpened image look at this figure in the [a href=\"http://www.imatest.com/docs/sqf.html]Imatest Documentation[/url]. Since the image was over sharpened, the SQF with standardized sharpening is lower than the image with standardized sharpening.

In the case of the Canon 400D, the image does not appear to be over sharpened since there is little overshoot in the edge plot and the image is reported as under sharpened by Imatest. When performing one's own tests, it is best to use raw apply no sharpening to the converted image.

Bill

[Ray]

Bill,
Perhaps these SQF procedures could be modified to produce an SDOFQF chart. (Subjective Depth of Field Quality Factor)   .

We could then refine standard DoF calculators by taking into consideration lens quality at the plane of focus as well as print size and viewing distance.

[bjanes]

Bill,
Perhaps these SQF procedures could be modified to produce an SDOFQF chart. (Subjective Depth of Field Quality Factor)   .

We could then refine standard DoF calculators by taking into consideration lens quality at the plane of focus as well as print size and viewing distance.
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Ray,

I take it you are being facetious?  


All of this information could be a bit difficult to implement at the time one is taking the picture. You might not know in advance the print size that will be used and other factors when you are adjusting the f/stop in order to optimize depth of field without running into diffraction limits.

Bill

[Ray]

I take it you are being facetious?   
All of this information could be a bit difficult to implement at the time one is taking the picture. You might not know in advance the print size that will be used and other factors when you are adjusting the f/stop in order to optimize depth of field without running into diffraction limits.
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Not completely facetious. I think it's doable   . There's at least one contributor to this site who claims to take into consideration print size factors when calculating distances and appropriate f stop for a certain DoF effect.

However, for a completley accurate result one needs to be able to measure distances accurately.

However, having got this completely accurate result in precise accordance with one's intentions, one then has the problem of communicating this result to the viewer.

In order to do this, might I suggest appropriately positioned viewing platforms in galleries for each print. Something along the lines, "Those with 20/20 vision please stand here to fully appreciate the intent of the author."  

Of course, we now have the complexities of individual vision acuity. Perhaps the photographer did not have 20/20 vision, so we need an algorithm to translate the photographers visual acuity into various standards that might correspond with the various standards of vision of the public at large.

Perhaps on the viewing platform we need various recommended positions for people with different eyesight problems.

Of course, the individual doesn't carry around such precise information about the condition of his/her eyesight.

That's fundamentally my point, without sarcasm.

[jani]

Perhaps on the viewing platform we need various recommended positions for people with different eyesight problems.

Of course, the individual doesn't carry around such precise information about the condition of his/her eyesight.

That's fundamentally my point, without sarcasm.

This is fundamentally a problem with the artist's vision.

I hereby submit my latest work, "2", which does not have these problems. There is no recommended viewing distance, just view it.

[attachment=2495:attachment]

[Ray]

This is fundamentally a problem with the artist's vision.

I hereby submit my latest work, "2", which does not have these problems. There is no recommended viewing distance, just view it.

[attachment=2495:attachment]
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Not sure about that, Jani. If the viewer is too far away, that dot might not be visible at all.  

[BJL]

I agree entirely with Jonathan's analysis. The DPReview tests show the Foveon sensors resolving above Nyquist. In his report, Phil did mention that there was some discussion whether they were observing useful detail or aliasing garbage. He decided the former, but I would submit that the latter is more likely.[a href=\"index.php?act=findpost&pid=117000\"][{POST_SNAPBACK}][/a]

I also agree, and some test patterns show very clear, classic signs of aliasing: as you move down the pattern of nine narrowing lines, other sensors just have them fade to gray, but with the SD10, the lines fade in and out, and towards the small end, the number of black lines appears to be different than the true value of nine: aliasing of a higher spatial frequency to a lower one.

One irony of this is that some years ago, a Foveon engineer said in an interview that Foveon X3 type sensors have resolution comparable to a Bayer CFA sensor of about twice the pixel count, corresponding to 1.4x more "line pairs per pixel" (which fits with tests  have seen and theory of luminance resolution dominated by green pixel data) and yet some X3 enthusiasts persist in claiming better resolution that that Foveon engineer.

(This is not the first time that enthusiasts claim more for a product that even the technical people at the company that makes it, leaving me skeptical: the often claimed imminence of Canon 35mmFF DSLR's at "mainstream enthusiast" prices is another of course.)

[Eric Myrvaagnes]

This is fundamentally a problem with the artist's vision.

I hereby submit my latest work, "2", which does not have these problems. There is no recommended viewing distance, just view it.

[attachment=2495:attachment]
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The highlights appear just a bit blown to me, but otherwise fine. I feel that "3" might be a better title, helping to bring out the metaphysical subtleties.  

Eric

[JeffKohn]

I think you are confusing the discontinued 3.43mp SD10 with Sigma's latest model the 4.6mp SD14.
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No, Sigma marketed the SD10 as a 10mp camera and they're marketing the SD14 as a 14mp camera. They can argue that technically that might be true in a way, but I still think it's highly misleading advertising.

[John Sheehy]

So here are some QE numbers, for Kodak sensors simply because Kodak lets it all hang out when it comes to sensor spec's, at http://www.kodak.com/US/en/dpq/site/SENSOR...iesRoot_product

KAF-10500, as in the Leica M8:
QE 40% green, 17% red, 32% blue.
That 17% red is anomolously low, and may be a typo.[a href=\"index.php?act=findpost&pid=116392\"][{POST_SNAPBACK}][/a]

If that's the sensitivity of the red channel for white (full visible spectrum) light, then it is not atypical at all.  Most CFA cameras are 40 to 60% as sensitive to red as to green, with blue usually in-between.

The only thing odd is that this camera has almost no IR filtration, which is usually the cause of low red sensitivity.

[Ray]

No, Sigma marketed the SD10 as a 10mp camera and they're marketing the SD14 as a 14mp camera. They can argue that technically that might be true in a way, but I still think it's highly misleading advertising.
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Ah! Yes, I see what you mean, but that's probably not the fault of Sigma. The confusion already existed in the use of the term 'pixel' before the SD9 was brought to market.

Before I even thought of buying my first digital camera, I understood that a pixel was a picture element consisting of a red, green and blue component. I was very unimpressed with the specs of those early 2mp and 3mp digital cameras until it was explained to me that those were all monochrome pixels that would be interpolated to what I understood as proper pixels.

I was still unimpressed, but a little less so. I knew that interpolated information is not completely accurate information.

If you are marketing a product and there's already ambiguity in the use of a term, it would be foolish (from a purely marketing point of view) to use the lower and less impressive figure.

[John Sheehy]

Before I even thought of buying my first digital camera, I understood that a pixel was a picture element consisting of a red, green and blue component.[a href=\"index.php?act=findpost&pid=118037\"][{POST_SNAPBACK}][/a][/

That understanding was based on a limited context of color monitor "pixels".

If you turn down the saturation on a monitor, you can use each of its color pixels as 3 B&W pixels.

[Ray]

That understanding was based on a limited context of color monitor "pixels".
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That may be true, but computer monitors were popular long before digital cameras.

I'm not commenting on the rightness or wrongnes of these different definitions but merely that they exist and are a source of confusion that wasn't created by Sigma.

Using the definition of pixel that is used when describing the number of pixels of a Bayer type sensor, Sigma are justified in describing the pixel count of their Foveon sensors by the same definition, but they would be wrong to claim that 10m of their pixels have the same resolving power as 10m Bayer type pixels. And I don't think they are claiming this.

[Ray]

If you turn down the saturation on a monitor, you can use each of its color pixels as 3 B&W pixels.
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let's be clear about this. Are you implying that my monitor, currently set at its maximum resolution of 1600x1280 pixels, can in fact be converted to a B&W monitor with a resolution of 4800x3840 pixels?

Oops! Good job I've got time to edit this so I can avoid making a complete pratt of myself. My monitor resolution is 1600x1200 of course and 3x the number of pixels equates to a resolution of around 2768x2076.

So, John, I desaturate my monitor and thereby increase its resolution to 2768x2076 for B&W images, or do I simply increase the bit depth???

[jani]

let's be clear about this. Are you implying that my monitor, currently set at its maximum resolution of 1600x1280 pixels, can in fact be converted to a B&W monitor with a resolution of 4800x3840 pixels?

Oops! Good job I've got time to edit this so I can avoid making a complete pratt of myself. My monitor resolution is 1600x1200 of course and 3x the number of pixels equates to a resolution of around 2768x2076.

So, John, I desaturate my monitor and thereby increase its resolution to 2768x2076 for B&W images, or do I simply increase the bit depth???

No, John is mistaken.

In RGB CRT displays, desaturation does not magically change the red, green and blue dots of phosphor into monochrome dots of phosphor.

RGB CRTs emulate greytones, just as RGB LCDs do.

[BJL]

If that's the sensitivity of the red channel for white (full visible spectrum) light, then it is not atypical at all.  Most CFA cameras are 40 to 60% as sensitive to red as to green, with blue usually in-between.

The only thing odd is that this camera has almost no IR filtration, which is usually the cause of low red sensitivity.
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Still, the red QE of this sensor is eggregiously low compared to other Kodak FF CCD's with micro-lenses:
KAF-10500: 17% R 40% G  32% B
One of similar vintage, same pixel size, also with off-set micro-lenses:
KAF-31600: 37% R 43% G  36% B
The slightly older one in the Leica R back, of same size and pixel pitch as the KAF-10500
KAF-10010: 34% R 40% G  36% B
The older one with smaller pixels in the Olympus E-300 and E-500:
KAF-8300:  33% R 40% G  33% B
The far older one in the Olympus E-1 withe the same pixel pitch as the KAF-10500:
KAF-5100:  31% R 34% G  31% B
Every other one has about twice the red QE as the 17% for the KAF-10500.

But indeed the graphs on page 12 of the spec. document [a href=\"http://www.kodak.com/ezpres/business/ccd/global/plugins/acrobat/en/datasheet/fullframe/KAF-10500LongSpec.pdf]http://www.kodak.com/ezpres/business/ccd/g...500LongSpec.pdf[/url] confirm it, and make me think that this was deliberate, a consequence of an attempt to avoid the need for an IR filter by effectively doing it in the CFA filters. I say that because the KAF-10500 sensitivity curves are extended far further into the IR than in the specs for other Kodak FF CCD sensors (to 1100nm instead of 700nm) and show a long flat tail of very low IR sensitivity, where with many other sensors, sensitivity picks up a bit at some point in the near IR, even in the B and G channels.

So maybe

[John Sheehy]

No, John is mistaken.

In RGB CRT displays, desaturation does not magically change the red, green and blue dots of phosphor into monochrome dots of phosphor.
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You're right, it doesn't.  I was thinking of something else from the past when I wrote that, where I simulated ~2560 shades of grey with the 3:6:1 R:G:B luminance ratios, and forgot that they did not increase virtual resolution.
My main point, however, is that a Pixel represents a 2D location and has nothing to do with color, whatsoever.  B&W displays have pixels, IR B&W cameras have pixels, etc.  "Pixels" have nothing generically to do with "RGB".

[Ray]

My main point, however, is that a Pixel represents a 2D location and has nothing to do with color, whatsoever.  B&W displays have pixels, IR B&W cameras have pixels, etc.  "Pixels" have nothing generically to do with "RGB".
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John,
Nevertheless, if I say my color monitor has a resolution of 1600x1200 pixels, I mean that it has 1600 groups of 3 phosphors in the horizontal direction and 1200 groups of 3 phosphors in the vertical direction. Each of the three phosphors of each group is designed to emit only one primary color when excited by the electron gun. They are color specific.

My knowledge of electronics is very limited, but I presume when I turn down the saturation of my monitor, I'm merely putting in place a set of instructions that causes all 3 phosphors in each group to be excited equally. It's the group of 3 that is called a pixel. Is this not the case?

[John Sheehy]

John,
Nevertheless, if I say my color monitor has a resolution of 1600x1200 pixels, I mean that it has 1600 groups of 3 phosphors in the horizontal direction and 1200 groups of 3 phosphors in the vertical direction. Each of the three phosphors of each group is designed to emit only one primary color when excited by the electron gun. They are color specific.

My knowledge of electronics is very limited, but I presume when I turn down the saturation of my monitor, I'm merely putting in place a set of instructions that causes all 3 phosphors in each group to be excited equally. It's the group of 3 that is called a pixel. Is this not the case?
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It's the case, but only because it's an RGB monitor, intended to be used to simulate a single RGB pixel.  Technically, each pixel is actually in three discreet 2D locations.  If it were representing a CFA of the same geometrical shape (without demosaicing), it could conceivably be considered to have 3x as many pixels, and have more spatial resolution.  Demosaicing is probably unnecessary when resolution is above the range of individual pixel recognition.