Downsizing Challenge Part 2: The Siemen's Star

[Andrea B.]

Yes. Agreed. Thanks Charlie.

Before going any further, I have to vent that I really do not want to have to perform stepped downsizes !!! But if that is where this effort leads, well, then.......at least I'll know what method is best even if I don't want to do it. 

I'm going to look for some other downsizing algorithms now.

[Frank Fremerey]

I rest my case. Your target audiences are Mac users with Retina Display and Apple Application Environment.

[Andrea B.]

Frank pay attention:  Charlie can see the photos here on two monitors which are NOT Apple - namely a NEC P221w and a Dell 20".

Charlie wrote:  This is apparent on my 13" Retina MCP, NEC P221w, as well as my cheap Dell 20" 2nd monitor.

[charlie]

I rest my case. Your target audiences are Mac users with Retina Display and Apple Application Environment.

I don't know that I am the target audience, but my NEC and Dell monitors are plugged into a Win 10 machine.

Before going any further, I have to vent that I really do not want to have to perform stepped downsizes !!! But if that is where this effort leads, well, then.......at least I'll know what method is best even if I don't want to do it. 

I hear you, who wants to drag everything into photoshop for downsizing?
Of course, what applies to this Siemen's Star pattern may not be necessary for real world photographs. I've been happy with my D800 downsizes coming out of Lightroom but I don't scrutinize the fine details excessively either. 

That said here is a (1) Photoshop CC stepped by 50% downsize (2) Photoshop CC direct downsize (3)and Lightroom direct downsize

[Andrea B.]

TEST:  Resize the Siemen's Star to 922 px width using Affinity which offers two versions of the Lanczos3 resizer and one version of a Bicubic resizer.

PHOTO 1:  Affinity Lanczos3 Separable downsize.
PHOTO 2:  Affinity Lanczos3 Non-separable downsize.
PHOTO 3:  Affinity Bicubic downsize.

CONCLUSION:  [Later]

[Andrea B.]

Charlie - THANKS for your downsizes !!! This is great to have. I don't have Lightroom, so it's great to have that one especially. I know so many people do use LR.

Can you please specify what Photoshop downsizing algorithm you chose?

Yes, I agree that downsizing a Siemen's Star may not necessarily hold for many 'real-world' images. But the high frequency of detail in this particular Star might be helpful for deciding which downsizing algorithm is best for D810 landscape images. We don't know yet.

The loss of center detail should be no surprise to anyone? We know we are going to lose that in a downsize. But how far from the center do we lose detail?

And has anyone noticed any chromatic aberration induced in some of the images? Or maybe we should call that "color artifacts induced by resizing".

[Andrea B.]

Edit Note:  I have to replace my Affinity downsizes because I accidently put 922 pixels into the resize box instead of 920 pixels. Duh!! I know 2 pixels likely make no difference, but I'm going to fix it anyway.

[simsurace]

Sorry to chime in so late. I hadn't noticed that you started a second thread.
To Frank or anyone who wonders why the Siemens star (original png) doesn't look like a Siemens star inside the smallest red circle:
At the periphery of the smallest red circle, the spacial frequency of lines is equal to the Nyquist frequency for the full-res image. Therefore, what is inside the smallest circle is stuff that can never be represented (resolved), not in the original png, and even less in any down-sized version of it.

(side-remark: if you print out a very high-res print of a Siemens star and photograph it, your lens will blur the central part because that part contains detail that is smaller than what the lens can resolve. If the lens is very sharp and can resolve it, your AA filter will take care of it. If even that fails, you will get interference patterns (moiré) in your raw file)

When downsizing, you want to make sure that you understand which is the circle that is closest to the Nyquist frequency of the downsized image. For example, if you downsize to ~1000px width, that would be the seventh circle (counting from the inside). Anything that is inside that circle is detail that exceeds the Nyquist limit, and will therefore exhibit false patterns (interference).

You want your sharpening to have a strength that gives a nice rendering of what's outside that circle, and not accentuate too much any false patterns within the circle.

[simsurace]

I have to remark that the LR direct downsize looks very good. It would be nice to know exactly what Lightroom does.
The Lanczos and bicubic blur the central part a bit too much in my judgement, making it almost in a uniform grey.

[simsurace]

Of course, what applies to this Siemen's Star pattern may not be necessary for real world photographs. I've been happy with my D800 downsizes coming out of Lightroom but I don't scrutinize the fine details excessively either. 

I'm happy if someone finds a case where a sharpening algorithm that works well on the Siemens star will produce a bad result on a real image. But I guess it would be hard to construct such a case.
If anything, I think that the Siemens star test yields makes one sharpen conservatively, leading to a sharpening amount that is on the low side of things.
You are happy with the LR resizes, great! Incidentally, it is also the algorithm that looks best so far on the Siemens star.
Let's all switch to LR then 

[charlie]

Charlie - THANKS for your downsizes !!! This is great to have. I don't have Lightroom, so it's great to have that one especially. I know so many people do use LR.

Can you please specify what Photoshop downsizing algorithm you chose?

The Photoshop examples were downsized with bicubic sharper. Lightroom was downsized with no output sharpening applied  I have included some more Lightroom examples with output sharpening applied. For those not familiar with Lightroom the export dialog box has an option for sharpening. Sharpening types includes Screen, Matte, & Glossy and strengths include Low, Standard, and High, no other adjustments or information is given. And for the record I am not at all familiar with Nyquist frequencies, limits, or Siemens star testing 

(1) no sharpening applied
(2) screen low setting and
(3) screen high setting.

[Andrea B.]

Thanks again Charlie.
My eyes have started to dance now from looking at all these lines. 

****

Simone, to be clear, the inner circle is #1?
Thus in concentric circle #2 we have the black space between the white lines increasing from 1px to 2px.
And in cc#3, the black spacing increases from 2px to 3px.
And so forth. (Eventually the white lines themselves seem to grow larger too.)

But -->>>>>> I'm not sure how to translate signal/sample statements to photographs!
The white/black pixels are equivalent to the sine wave peaks?
So, Nyquist tells us that we need at least a 2 pixel width sample in order to resolve pixel detail?
Thus any resizing which does not preserve that destroys detail?
Am I anywhere in the ball park? 

I've resized everything (and Charlie too) to 1/8 the original size, so my 2 pixel sample should move out to the 7th? or 8th? circle?
 

[Andrea B.]

TEST:  Compare two Bicubic Sharper downsizes. The first had a 1px Gaussian Blur applied before the downsize. The second did not.

Photo 1:  Gaussian blur before downsize.
Photo 2:  Downsize only.

[simsurace]

Simone, to be clear, the inner circle is #1?
Thus in concentric circle #2 we have the black space between the white lines increasing from 1px to 2px.
And in cc#3, the black spacing increases from 2px to 3px.
And so forth. (Eventually the white lines themselves seem to grow larger too.)

But -->>>>>> I'm not sure how to translate signal/sample statements to photographs!
The white/black pixels are equivalent to the sine wave peaks?
So, Nyquist tells us that we need at least a 2 pixel width sample in order to resolve pixel detail?
Thus any resizing which does not preserve that destroys detail?
Am I anywhere in the ball park? 

I've resized everything (and Charlie too) to 1/8 the original size, so my 2 pixel sample should move out to the 7th? or 8th? circle?

Actually, your questions just made me realize that during the export from the program I used to make these star patterns, something went wrong. The black lines got too thick and the whites too thin.

I wanted them to be a sine, so the white and black should be equal in size. I will post another version where this is corrected.

The period of the sine is two pixels long at circle #1. It is 4 pixels long at circle #2. It is 6 pixels long at circle #3. Etc. At least that's how I planned it to be, and I will just shortly upload another file where this is the case. In the file that you have been using so far, the black parts are too thick, but the spacing is still correct. There is 4px worth of space between the start of one black line to the next at circle #2.

Nyquist tells us that when the sine grating is horizontal or vertical, it cannot have a frequency of less than one cycle per two pixels. That would be one black line followed by a white line followed by a black line (in the best case scenario where the grating is in phase with the pixel grid).

Resizing will never preserve that detail, since in the resized image the smallest detail is still one cycle per two pixels, but that detail was much bigger in the original file. The detail which is smaller than that needs to be toned down in order to avoid these interference patterns inside the new Nyquist circle.

[Andrea B.]

Thanks!  We will start over when we get the new star.

"One cycle per two pixels" is the phrase I was looking for. Thanks again!