Very interesting on whether camera resolution matters with a lousy lens

[ErikKaffehr]

Hi,

Jeff Schewe says that native resolution of Epson printers is 360 PPI or 720 PPI. He also says that the images are always resampled to 360 PPI or 720 PPI in the printer driver.

As Jeff used to work with Epson evaluating new technologies I assume that he has good info on the subject.

Best regards
Erik

Trying to make a direct comparison of a dithering printer to a continuous tone device is a fools errand.  There is a 1-1 correspondence between image pixels and printed output with each pixel being any one of the total number of colors the continuous tone output medium has to offer. 

Epson (all inkjets) have a limited color set.  The hardware has the ability to place a certain number of drops per linear inch in each dimension of a specific size and specific color.  This is where the 360, 720, 1440 and 2880 numbers come from.  But there is no direct correspondence between a droplet and a pixel.  The apparent resolution of the image is significantly impacted by the substrate on which the ink is placed (how much ink can be laid down and how much spread of the drop occurs).

I have owned just about every Seiko Epson Stylus Photo desktop printer ever made.  I also worked on a government program with Epson.

Some Points directly:

1. Epson printers do not resample the image prior to passing through the dithering algorithm

2. The minimum resolution that should be sent to the printer reasonable quality output is 180ppi

3. The algorithm performance tends to top out at around 300-360ppi, except for images with specific characteristics (Epson declined to identify these characteristics) when higher pixel densities might yield marginal increases in apparent quality.

4. Only up sample an image if the up sampling provides a benefit to the image itself.  It is not beneficial to up sample an image merely to provide the dithering algorithm with more data.

5. Long time Epson users will verify that sending multiples of 60ppi is best and that, in general, 360ppi is a good standard.  Some will say that 720ppi is also reasonable.  What I will say is stay away from resolutions not quite a multiple of 60ppi.  For example, don't use 359ppi!  Better to be 330ppi than 355ppi for example.  This is because of how the algorithm itself handles the data prior to the dithering.

[ErikKaffehr]

Hi Bart,

Thanks for chiming in. My posting was essentially intended to shed some light on valid comparisons between image sizes. Should we size up or down. I agree with the points you make mostly.

Just to make a small point, the 360 PPI corresponds to one minute of arc at 25 cm, which is often regarded the resolution limit of human vision, simply because human vision cannot normally focus closer than 25 cm. But, all men and women are not created equal. I should know as I am near sighted.

I sort of bumped into this. I was complaining about staircase/zipper artefacts produced by a certain combination of sensor, lens and raw converter. An experienced printer pointed out to me that he could observe these artefacts with a loupe but not with naked eye in a large print (like 100x150 cm). I repeated the experiment and found that I could actually see the artefacts in good light, without corrective lenses. Keep in mind I am near sighted. With corrective glasses I couldn't observe them. Of course neither progressive glasses or reading glasses are made for 25 cm. But yes, young people with perfect vision may observe things not visible to older people.

The point on vernier acuity is very interesting, of course. I would also agree that higher resolution helps with post processing workflow.

For me, the most important advantage of high resolution is that it is helpful in suppressing aliasing artefacts, but I don't really feel that the 36-50 MP we have on DSLRs is sufficient to fully suppress aliasing.

Best regards
Erik

Hi Erik,

Yes, 300 - 360 PPI is a good match for human visual acuity at normal reading distances, at good illumination levels. However, the printer is actually printing at 600 PPI or 720 PPI, unless we reduce that to 300 PPI or 360 PPI by not selecting the proper settings. This may seem overkill, if we cant see it why would we do it, one could ask? Well, there can be subject matter that is resolvable by eye and that exceeds the average 20/20 vision acuity, calling on the Vernier resolution capability of our vision, AND with more (smaller) pixels to print we can use better output sharpening.

While I agree that, also due to larger viewing distance, we can print with quite a nice image quality at the lower PPI choices, there is a distinct benefit to using the higher resolution settings, even if that means we need to upsample the output before sending it to the printer. When one uses high quality upsampling software, e.g. PhotoZoom Pro, one can even increase resolution of edge detail beyond what the camera sensor has to offer.

There is also a chance that, on certain subject matter, what looks like aliasing is just bordering on aliasing but due to interference the detail looks crude/rough/pixelated, but once upsampled it looks correct because it was not really aliased.

In principle yes but, given the choice, who could object to better image quality also when viewed from shorter distances. The viewing experience becomes a lot more immersive, and material structure is much better depicted with more than barely adequate resolution.

And as to the OP's question, improving sensor resolution will always improve the captured lens quality, because denser sampling of the projected lens image will boost the overal MTF and increase limiting resolution. As others have said, component MTFs multiply to achieve an overall system MTF, and it's the worst contributing component that sets the achievable ceiling. Sensors are usually worse at resolving detail than decent lenses, so usually most gain is to be had by increasing sensor resolution (which also opens opportunities for signal restoration with dedicated software).

Cheers,
Bart

[dwswager]

Hi,

Jeff Schewe says that native resolution of Epson printers is 360 PPI or 720 PPI. He also says that the images are always resampled to 360 PPI or 720 PPI in the printer driver.

As Jeff used to work with Epson evaluating new technologies I assume that he has good info on the subject.

Best regards
Erik

And you would be wrong.  Jeff has tremendous empirical experience with Epson output, and following his tips will lead to great images, but he still believes that the image is resampled.  He has finally accepted Epson's assertion that the driver doesn't do it, but now believes that the Operating System does it.  While if you have a developers kit installed it is fairly easy to trace the data and prove otherwise, at least on the Windows Platform.

A dithering printer doesn't have a "Native" resolution.  Epson printers have  various increments of linear distance that it can put down a drop.  But it will never put down a constant number of drops per inch over an entire page in the manner a continuous tone printer like Dye Sublimation does.  It will mix various colors, sizes and placements across the page to give the impression of continuous tone, but if you look close enough, you will still see the dither pattern.

[ErikKaffehr]

Hi,

My interpretation would be more that the dithering is optimised for 360 PPI and 720 PPI respectively. Would be much interesting to have Jeff's input on this.

This is actually quite important. Jeff's recommendation was to always print at 360 or 720 PPI and let Lightroom do the scaling.

Best regards
Erik

And you would be wrong.  Jeff has tremendous empirical experience with Epson output, and following his tips will lead to great images, but he still believes that the image is resampled.  He has finally accepted Epson's assertion that the driver doesn't do it, but now believes that the Operating System does it.  While if you have a developers kit installed it is fairly easy to trace the data and prove otherwise, at least on the Windows Platform.

A dithering printer doesn't have a "Native" resolution.  Epson printers have  various increments of linear distance that it can put down a drop.  But it will never put down a constant number of drops per inch over an entire page in the manner a continuous tone printer like Dye Sublimation does.  It will mix various colors, sizes and placements across the page to give the impression of continuous tone, but if you look close enough, you will still see the dither pattern.

[Dan Wells]

The point on dithering is an interesting one - the printer's processor

1.) Takes in an image at whatever DPI
2.) If it's not at one of the standard DPIs (it seems like they may be 300/600 for Canon, 360/720 for Epson), resamples through a simple algorithm to those standard resolutions(Erik's post today suggests this may actually be part of step 3)
3.) Dithers to the variable dot-size pattern laid down in 11 or 12 colors at a very high resolution, so when it's viewed, it looks (without a loupe) like a continuous tone).

Regardless of whether the resample happens as part of the dither or in a separate step, there is no way of producing the dither without having a known relationship between pixels in the input datastream and area taken up on paper - there's an EFFECTIVE resample happening SOMEWHERE. Most good drivers (Lightroom's internal driver, QImage, ImagePrint (which also uses its own dither!)) eliminate that scaling step by sending the data at the correct size (performing an explicit resample with a more sophisticated algorithm). Except in the case of ImagePrint (which sends predithered data right to the head), the driver probably performs some sort of implicit scaling when dithering, but that scaling is meaningless because it's 1:1 with the image at the desired size

[Jack Hogan]

It is not that simple in practice. MTFs do multiply, but one must convert from the spatial domain to a frequency domain by first performing a Fourier transform, multiply the MTFs, and then convert back to the spatial domain as explained by Norman Koren here (scroll down to the Imaging Systems section). Not being an expert in these matters, I don't how one would do this in practice.

I am not an expert either, but it turns out that it is not that difficult for a test image well focused in the center, captured with good technique all other things being equal.  In such a case the final MTF in the center of the image is mainly the product of three (or four) MTF curves, of which two (or three) are well known: diffraction (as a function of f-number), pixel aperture (as a function of pitch) and lens blur (often unknown).  If the sensor has an antialiasing filter the fourth MTF curve is the AA's (as a function of the spreading distance, easy to estimate).  That's it.

So if you are measuring system MTF off a slanted edge in the center of the field of view, for instance, if only one variable is improved while keeping everything else the same (e.g. pitch is reduced) we can pretty well guarantee that it's going to improve the overall reading throughout the curve, in some parts more than in others.  It's not too difficult to estimate approximately by how much in a given situation, but we'll leave that for another time.

Jack

[dwswager]

My interpretation would be more that the dithering is optimised for 360 PPI and 720 PPI respectively. Would be much interesting to have Jeff's input on this.

This is actually quite important. Jeff's recommendation was to always print at 360 or 720 PPI and let Lightroom do the scaling.

The point on dithering is an interesting one - the printer's processor

1.) Takes in an image at whatever DPI
2.) If it's not at one of the standard DPIs (it seems like they may be 300/600 for Canon, 360/720 for Epson), resamples through a simple algorithm to those standard resolutions(Erik's post today suggests this may actually be part of step 3)
3.) Dithers to the variable dot-size pattern laid down in 11 or 12 colors at a very high resolution, so when it's viewed, it looks (without a loupe) like a continuous tone).

Regardless of whether the resample happens as part of the dither or in a separate step, there is no way of producing the dither without having a known relationship between pixels in the input datastream and area taken up on paper - there's an EFFECTIVE resample happening SOMEWHERE. Most good drivers (Lightroom's internal driver, QImage, ImagePrint (which also uses its own dither!)) eliminate that scaling step by sending the data at the correct size (performing an explicit resample with a more sophisticated algorithm). Except in the case of ImagePrint (which sends predithered data right to the head), the driver probably performs some sort of implicit scaling when dithering, but that scaling is meaningless because it's 1:1 with the image at the desired size

This is the fallacy that the image is resampled at all!  A continuous tone device must resample to it's native resolution because it is obligated to put a dot (pixel) of a specific color at a specific location with a set pitch to the next dot across the entire page.  Assuming a 300dpi continuous tone printer, then the printer lays down 300 dots per inch across the entire page.  To get from the total pixel dimensions given to the printer to printed output it must resample unless the resolution exactly matches the printer dpi x dimensions.

A dithering printer doesn't operate that way.  It has a set of droplet locations per linear inch, droplet sizes and droplet colors at it's disposal.  It also knows the characteristics of the media from the selection in the driver.  From this data, it must create a pattern of dots varying is number, spacing, size and color to give the appearance that represents what the original data looks like.  It might lay down 340 drops in one linear inch and then only 310 in the next measured linear inch.  Epson printers do not lay down a consistent 360dpi or 720dpi.  The settings for higher quality in an Epson driver are merely changing the constraints on the dither algorithm.  That is it is allowing more locations to be used in the computation.  However, that does not mean that in any linear inch, it will actually use all those available locations. 

Bottom Line is if you follow Jeff's recommendations, you will get great output.  My point is that because he believes the image is resampled, he neglects other options that might result in similar results consuming less resources or even better output.  For example, assume you have an image at 480ppi.  Jeff's recommendations would have you either down sample to 360ppi or up sample to 720ppi.  He neglects the option of using 480ppi directly (even multiple of 60ppi) because he believes it will be resampled while Epson says it won't.

I've tested this with a 540ppi image that I printed at 540ppi, 360ppi and 720ppi.  In general, I find essentially no difference in the images printed on Epson Exhibition Fiber or Epson Hot Press Bright.  There have been images where I think I might have seen a difference, but couldn't really say one was better than the other and if you put the 3 side by side, I certainly don't think I could tell you which was which.  Your eyes might say otherwise.

[Bart_van_der_Wolf]

This is the fallacy that the image is resampled at all!

Here we go again, we have discussed this before, you are still demonstrably not correct. Printer drivers do resample, as can be easily verified by printing a e.g. 359 PPI or 361 PPI image to the same dimensions, but now at 360 PPI. Use a simple 1 pixel wide alternating vertical black and white line pattern across a reasonable width of the image and the printed result will show aliasing, completely predictable and consistent with resampling. A 361 PPI image at 10 inches wide would be 3610 pixels wide. try printing those 3610 pixels over a width of exactly 10 inches at 360 PPI. Those 3610 pixels will need to be squeezed into the grid for 3600 pixels, which is done by resampling, and aliasing is the result. If there is no resampling, there would be no aliasing.

The simple experiment has been performed by several people here on LuLa, and the outcome was, ... aliasing. The only way to mitigate the issue is by using additional dithering to the output data, i.e. on top of the normal dithering for intermediate ink colors.

A bit more background on the differences between Mac OS and Windows printer drivers is discussed here.

If you really want to torture test your printer's capabilities, which includes detection of head-alignment and paper transport issues, feel free to use my printer and output medium test target, as described here.

Cheers,
Bart

[kers]

...
The two images show nearly as much difference as the two captured with the great lens. No, the sharp image is not as sharp, but the degree of improvement is NOT that different. I'm assuming his test conditions were decent, although he doesn't go into any detail, he's been around the Canon world a long time, and is well respected....

Hello Dan,
I am not surprised...
if we look at sharpness only;
The center of most lenses are usually able to do 50MP when stopped down. It is the sides that make the difference...
Even good lenses have problems at 36MP at the sides of full frame- not to mention the corners...

To show you the resolution of a good lens in the central area i attach two 100% central crops -A and B - both shot with the same good lens - the nikkor 45mm PCE @F8
A is taken with a Nikon1-J5 20MP and B taken with a D810 ( 36MP full frame) and Upsampled to the size of the Nikon1-J5 output.
the Nikon1 J5 captures the central 13,2 x 8,8 mm area and with this resolution a full frame sensor would be 154 MP.

As you can see the quality is really good even @ 150MP!
In the case of this lens i can even make an almost fully shifted image with the nikon1-J5 that looks good.
(@ f5.6 the central sharpness is even better, but shifted it is less)

[dwswager]

Here we go again, we have discussed this before, you are still demonstrably not correct. Printer drivers do resample, as can be easily verified by printing a e.g. 359 PPI or 361 PPI image to the same dimensions, but now at 360 PPI. Use a simple 1 pixel wide alternating vertical black and white line pattern across a reasonable width of the image and the printed result will show aliasing, completely predictable and consistent with resampling. A 361 PPI image at 10 inches wide would be 3610 pixels wide. try printing those 3610 pixels over a width of exactly 10 inches at 360 PPI. Those 3610 pixels will need to be squeezed into the grid for 3600 pixels, which is done by resampling, and aliasing is the result. If there is no resampling, there would be no aliasing.

The simple experiment has been performed by several people here on LuLa, and the outcome was, ... aliasing. The only way to mitigate the issue is by using additional dithering to the output data, i.e. on top of the normal dithering for intermediate ink colors.

A bit more background on the differences between Mac OS and Windows printer drivers is discussed here.

If you really want to torture test your printer's capabilities, which includes detection of head-alignment and paper transport issues, feel free to use my printer and output medium test target, as described here.

Cheers,
Bart

The 359ppi and 361ppi test is specifically demonstrating the data handling phenomena that occurs because the driver works in 60 x 60 pixel blocks of data.  It is specifically why even multiples of 60 have been recommended since 1994.  It is why Epson recommends a minimum of 180ppi (even multiple of 60) for quality output.  Neither the OS, nor the DRIVER resamples the image!  Epson has been vehement about this since the original printer!   Even Jeff finally relented and now blames the supposed resampling on the OS. 

Print  2 samples one at 300 and one at 360 and look at the differences.  They will not exhibit the same phenomena!  In fact, print at 330 and you won't get that either.

At the end of the day, it really doesn't matter.  Most people will just follow the rule that the printers algorithm tops out at 360ppi and will use that.  Others will upsample to 720ppi which is another multiple of 60 and it won't matter and the rest will use even multiples of 60 from what they have to 720ppi as the mood strikes them.  No one is going to be foolish enough to send 359ppi or 539pp to the printer.

[Wayne Fox]

If what you say is true and no  resampling is occurring, why would using even numbers of 60 be important?  We’ve always be led to believe that the native dpi of the epson driver is 360 so using numbers that divide evenly by 60 yields the best results.

Also curious what would cause the aliasing in Bart’s test other than resampling ? there have been other examples of this discussed here. 

Again, you are right it doesn’t really matter, best practice is to use good program to get the data to 360 before sending it to the printer.  Just sort of curious.

[Bart_van_der_Wolf]

If what you say is true and no  resampling is occurring, why would using even numbers of 60 be important?  We’ve always be led to believe that the native dpi of the epson driver is 360 so using numbers that divide evenly by 60 yields the best results.

Sounds like yet another urban legend, to me anyway. Integer divisions of 360 (360/2=180, 360/3=120, 360/4=90, 360/5=72, 360/6=60, etc. ) will produce evenly spaced aliasing patterns, almost like an intended pattern (instead of uniform gray, the average between black and white). Maybe that looks more acceptable, but it is still aliasing caused by maximizing and minimizing the contrast when the resizing happens to align/aliase with the grid.

Cheers,
Bart

[Stephen Ray]

Some print resolution number trivia…

Begin with a Hasselblad sensor size of 40 Megapixels (5478 x 7304),
Specify a gallery print size of 40x50.333 inches (keeping the exact 3x4 aspect ratio) @ 180 ppi,
Result file pixel size will be 7200x9600 =
Coincidentally numbers used in Epson printer model names?

Many common aspect ratios such as 2x3 to make 20x30, 30x45, 40x60; 3x4 to make 20x32, 30x40, 40x53.333; 4x5 to make 24x30, 40x50, 48x60, etc., @ 180, 240, and 360ppi can result in curious number revelations too.

An amazing feat is that the engineers can design & manufacture something as small as a Canon sensor to an exact 2x3 aspect ratio and I can then enlarge those individuals rows and columns of pixels to a 40x60 to a machine such as an Epson 11880 to deliver a print to the exact size. Amazing because…

…sometimes machines are not so behaved and accurate. There is sometimes an ugly truth called print size/length compensation, print size calibration, print size off-set, print scale correction, media advance calibration, scale adjust, etc., common especially to users of professional printers making rather long prints. Most RIPs have this control and it’s often a moving target.

Pixel stretching? I think the engineer's term is subsampling.

Using subsampling, a continuous-tone devices such as Fuji Frontier, Noritsu, Lightjet, Chromira, Lambda can deliver discernible individual red, green, and blue pixels on a white, gray, or black background @ their native resolutions. Usually somewhat soft however because of subsampling and halation but still amazing especially if any print size compensation is involved, as it usually is.

[tnargs]

...The two images show nearly as much difference as the two captured with the great lens. No, the sharp image is not as sharp, but the degree of improvement is NOT that different. I'm assuming his test conditions were decent, although he doesn't go into any detail, he's been around the Canon world a long time, and is well respected.

Back to the OP, wouldn't it have been more interesting to see the 6D images interpolated instead of merely upscaled? Especially the 'lousy lens', I am not sure that we are reacting more to the blockiness than to the information.

[Bart_van_der_Wolf]

Back to the OP, wouldn't it have been more interesting to see the 6D images interpolated instead of merely upscaled? Especially the 'lousy lens', I am not sure that we are reacting more to the blockiness than to the information.

Yes, good point. It was also mentioned by others, that the upscaling/interpolation method (and subsequent sharpening) can make a difference as well.

Cheers,
Bart

[Wayne Fox]

Sounds like yet another urban legend, to me anyway. Integer divisions of 360 (360/2=180, 360/3=120, 360/4=90, 360/5=72, 360/6=60, etc. ) will produce evenly spaced aliasing patterns, almost like an intended pattern (instead of uniform gray, the average between black and white). Maybe that looks more acceptable, but it is still aliasing caused by maximizing and minimizing the contrast when the resizing happens to align/aliase with the grid.

Cheers,
Bart

It's pretty outdated now, but I believe when it was popular several years ago (should have indicated that in my post I was talking about an outdated concept), the theory was the epson driver resizing was weak so forcing it to be an even number would give the best results.  I think the other popular thing back then was to enlarge it was better to do so at 10% increments up to the final size.  but the concept came from the idea that somewhere in the pipeline the image would be resized to the machines "internal" dpi of 360 or 720.

I think most now resize to either 360, either by creating a secondary file or using something like LR.  And as you pointed out, that doesn't eliminate aliasing, just sort of create  different type of aliasing.

[Farmer]

This issue always ends up being confused when people treat PPI and DPI as the same thing.  There is no 1:1 relationship between pixels and printer dots except, perhaps, in pure tones of the printer's inkset and even then, it depends on so many things that it's very unlikely.

[dwswager]

If what you say is true and no  resampling is occurring, why would using even numbers of 60 be important?  We’ve always be led to believe that the native dpi of the epson driver is 360 so using numbers that divide evenly by 60 yields the best results.

Also curious what would cause the aliasing in Bart’s test other than resampling ? there have been other examples of this discussed here. 

Again, you are right it doesn’t really matter, best practice is to use good program to get the data to 360 before sending it to the printer.  Just sort of curious.

It's the boundary conditions surrounding the 60x60 macro blocks of data.  359 and 361 end up being 1 pixel off an even multiple of 60.  No one ever tries it at or 479/481 or 539/541 because of the wide spread belief that the printer resamples the image to 360.

There are really only 3 things that one can believe:

1. No resampling occurs - One is then obligated to explain the phenomena that happens with images at 359ppi for example.

2. The Driver Resamples the image - One is obligated to believe that Epson has been lying for years!

3. The OS (Mac and Windows) resample the image - One is obligated to believe that Apple and Microsoft colluded with Epson to have their respective OS resample images to 360ppi and 720ppi rather than some other resolution or not resample at all.  This one is just a little conspiracy theory nutty for me.

[Slobodan Blagojevic]

Forget about 300, 360, 600, 720, etc. dpi. How about 127,000 dpi?

http://fortune.com/2015/12/17/smallest-artwork-printing-mona-lisa/?xid=smartnews

[ErikKaffehr]

Hi Slobodan,

What would the standard viewing distance be? Also, I think they need to put some effort in generating colour profiles for that device…

Best regards
Erik

Forget about 300, 360, 600, 720, etc. dpi. How about 127,000 dpi?

http://fortune.com/2015/12/17/smallest-artwork-printing-mona-lisa/?xid=smartnews