FZ200 Diffraction Limit - Panasonic Tech Service

Started Aug 27, 2013 | Discussions thread
sherman_levine
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Re: FZ200 Maximum Desirable F-Number to achieve adequate "Sharpness"
In reply to J C Brown, Sep 4, 2013

J C Brown wrote:

sherman_levine wrote:

Detail Man wrote:

sherman_levine wrote:

J C Brown wrote:

I too have adopted a relatively simple approach to assessing and measuring the resolution of a digital camera as described in my FZ50 report which is available for download as a 6 MB PDF file from here.

As discussed in Section 2 of that report, due to the effect of the edges of the lines of a black and white grid partially overlapping adjacent pixels, the resolution of a line pair, i.e. one black line and one white line, requires three pixels, i.e. 1.5 pixels per line width. Consequently the maximum resolution of a digital camera can be estimated with reasonable accuracy by dividing the number of pixels in the height of the sensor by 1.5.

Thus for the FZ200 which has a 4000 x 3000 pixel sensor the maximum resolution would be estimated to be 2000 lines per picture height, LPH. That value is within 5% and 10% respectively of the vertical resolution values for the JPEG and RAW images in the DPR FZ200 review.

Jimmy,

With your most recent stepped-baseline chart, where you select the smallest line in which one E has all 5 bars (B-W-B-W-B) visible, it seems to me that "perfect" zero-diffraction optics would yield one-pixel-per-line resolution (i.e. 1500 B-W pairs in the 3000-pixel high FZ200 sensor). The 1.5 pixels per line calculation (1000 B-W pairs...) would apply if your criterion were "the smallest line in which all the Es have all 5 bars visible).

Is that not correct?

One thought that occurs to me is that line-pair patterns are composed of a series (of odd integer multiples, amplitude-scaled in inverse proportion to the harmonic-number) spatial frequency "lines" of periodic variations - representing a periodic "square wave" in the spatial domain.

So, rather than being a single sinusoidal "line" of periodic variation in space represented in the spatial frequency domain at the Shannon-Nyquist spatial rep-rate that you are proposing (equal to the spatial sampling frequency divided by 2), we are talking about the additional presence of 3rd, 5th, 7th, etc., harmonics that will result in spatial frequency domain aliasing-distortion products.

Additionally, one is not ever able to physically line up the rows/column of photosites on an image-sensor with the line-pairs as projected onto the image-sensor surface. Results will be essentiall random (as to the relative phase relationships between the projected image and photosites).

It seems a wonder that an alternating dark/light line-pair can be resolved by only 3 photosites ...

The characters on Jimmy's chart do not share a single baseline, but rather one which slopes upward by 1/10 of a (projected) pixel per character.

Consequently, the "Which is the smallest line where I can find one good E?" test seems capable of testing the 1:1 situation.

Sherm,

Your assessment that "Consequently, the "Which is the smallest line where I can find one good E?" test seems capable of testing the 1:1 situation" is entirely correct.

Unfortunately in order to achieve that in practice, even with a perfect lens and sensor, it would be necessary for the image of the vertical scale line to be exactly 400 pixels long and for the edges of the image of the first and last E in each group of eleven to be in exact register with the edges of the pixels on the sensor. IMHO even in the best of laboratory condition it would be extremely difficult if not impossible to achieve that.

The following image shows a comparison between a group of eleven 1.0 pixel black Es, a graphical simulation of the response of a grey-scale only sensor and crop from an FZ50 test image for which the scale and the alignment had been adjust very carefully to meet the requirements described above.

FZ50 test image compared with image of 1.0 pixel section of test chart and a graphical simulation of the response of a grey-scale only sensor to the 1.0 pixel Es.

As can be seen from the lower part of the above image even with very careful adjustment of the photographic scale and alignment my FZ50 has failed to record an accurate image of any of the eleven E in the test chart.

The following image shows an equivalent comparison between a group of eleven 1.5 pixel black Es, a graphical simulation of the response of a grey-scale only sensor and crop from the same FZ50 test image.

FZ50 test image compared with image 1.5 pixel section of test chart and graphical simulation of the response of a grey-scale only sensor to the 1.5 pixel Es.

As can be seen from the above image the FZ50 has succeeded in recording fairly accurate representations of the 1.5 pixel Es all of which are recognisable as an E and IMHO very similar in appearance to the graphical simulations of the expected images.

I hope that you will find the above images and comments helpful in explaining the reasoning behind the design of my test chart.

Jimmy

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J C Brown

OK - Thanks - Sounds like I was wrong about the "look for the line with one visible E and compare that to 1.0" criterion and should use instead the "look for the line with all Es visible and compare that to 1.5 criterion for "perfect"

Is that correct?

Sherm

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