Monochrome Camera / Techniques?

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dolmadis
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Re: Monochrome Camera / Techniques?

Post by dolmadis »

Thanks Ray.

An intricate lighting design in every way which has rewarded you with fine imaging.

I have learnt a very great deal visualising the set up and must thank you very much for sharing given that it is the product of many hours work.

BR

John

Steve S
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Re: Monochrome Camera / Techniques?

Post by Steve S »

I've had a full-spectrum monochrome conversion of a Sony A7RM3 for a couple of years, conversion done by Monochrome Imaging and with Astronomik band-pass filters behind the lens. I've used it pictorially with IR-pass filters, with visible-light filters and with the latter supplemented with old-fashioned b&w filters in front of the lens. There is a certain agreeable archaism about banging away at, say, a grain elevator with a Wratten #29 on the lens, but in my experience images taken at the same time with a straight-stock A7RM4 are very similar to those from the converted camera, after conversion to monochrome in LR or C1 and some fiddling with the color sliders.

For static objects illuminated by white light, surely the venerable color-separation approach, as with tri-color cameras and the original Technicolor process, is entirely obviated by pixel-shift, now available on a number of digital cameras.

I did once do a careful shoot-out between the converted A7RM3 and the M4. The subject was a very large bookcase with a small part of my wife's formidable collection of books on food and cooking, the lens the 65mm Apo Lanthar at f/5. Lots of dust jackets with half-tones to evaluate moire, and lots of cloth bindings for the same. After matching the tonality of the two images, I pixel peeked for perhaps an hour trying to decide which image had more real detail or was for some other reason preferable. For any practical or aesthetic purpose, the images were entirely interchangeable. The linear resolution advantage of the R4 is about 20%, so this is quite consistent with what jmc reports above. One qualification: I sprinkled a few USAF 1951's around the shelves, and the finer line patterns on them erupt into kaleidoscopic patterns of false color with the R4, and the extinction-resolution advantage of the de-Bayered R3 is considerably greater than that 20%. This could be established by tedious micro-densitometry of a type I did over sixty years ago (OMG!), but no need. The false color on the resolution charts is not obtrusive on the book spines, with just traces of moire in a few places on each image.

Again, if you need some particular wavelength band-pass, you know who you are. If you're interested in white light and you have a static subject, go with pixel shift.

ray_parkhurst
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Re: Monochrome Camera / Techniques?

Post by ray_parkhurst »

Thanks for the detailed reply Steve. I tried a A7Rm4 when they first came out, but was not happy with the look of the rendered pixel-shift image. It showed evidence of excessive sharpening and false details at 100%. This was with a fairly early version of Imaging Edge. A later version gave some user control, but even at the minimum sharpening settings there was still too much processing for my use. Even later there was a 3rd party program that rendered into dng file IIRC, and then another program was needed to create the final tiff or jpg for stacking or tiling. This workflow seems a bit onerous so I have not made the plunge to try the A7rm4 again.

There are of course other pixel-shifting cameras such as the Panasonic S1R plus offerings from Olympus, and Lou Jost has been a strong proponent for these. So far I have not seen evidence that their 100% images are sufficiently realistic vs the A7Rm4 so I have not made the decision to go with one of these. At some point I may chance it anyway since you may be right that the best way forward is with pixel shifting. Based on what I've seen pricing-wise, it is certainly a more economical approach.

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Re: Monochrome Camera / Techniques?

Post by ray_parkhurst »

rjlittlefield wrote:
Fri Sep 04, 2020 5:57 pm
Is this from your HR T2i, so, 18 megapixel APS-C sensor with AA filter removed?

--Rik
Rik...what was the reason for your question? The lens is not quite as sharp as the Macro Varon I usually use for this magnification, but it does have other qualities that make it perhaps more useful. For full-coin single or stacked images, I'm not as concerned about extreme detail, just the overall image quality. My concern with 100% IQ is with the stack and stitch images at higher magnification. The image above is a single image, not stacked, so it lacks some sharpness that it could have if I had done a shallow stack. Were you concerned about the IQ? Or was there some other reason for the question?

rjlittlefield
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Re: Monochrome Camera / Techniques?

Post by rjlittlefield »

ray_parkhurst wrote:
Sat Sep 05, 2020 4:26 pm
Or was there some other reason for the question?
Often questions pop to mind that I'm not sure exactly what the reason is. This is one of those.

I think I was trying to get an idea what a "reference-quality full-coin image" might need, and it was easier to ask about pixel counts than to try figuring it out from the images.

It does help to know that this is single shot, and not as sharp as your usual stacks.

--Rik

iconoclastica
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Re: Monochrome Camera / Techniques?

Post by iconoclastica »

rjlittlefield wrote:
Fri Sep 04, 2020 9:31 am
I don't see any way to hide the presence of a Bayer filter unless color is perfectly constant.
Wouldn't a band-pass filter in front of the lens do this trick?

My motivation for going monochrome was to simply eliminate the Bayer filter so I could take advantage of full resolution of the sensor.
I said something similar in a discussion last week and then someone asked me whether it wouldn't be easier to move to one of these modern 50MP cameras. Wouldn't it? I haven't got a reply yet..
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Lou Jost
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Re: Monochrome Camera / Techniques?

Post by Lou Jost »

Wouldn't a band-pass filter in front of the lens do this trick?
No, not if you want to photograph luminance. With a narrow-band filter or monochromatic light, the only things that will be bright in the image are things of that color.

"someone asked me whether it wouldn't be easier to move to one of these modern 50MP cameras. Wouldn't it?"

As I mentioned above, pixel-shifting on modern cameras provides a cheap easy method to get monochrome.

Steve S
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Re: Monochrome Camera / Techniques?

Post by Steve S »

Ray, you had expressed concern about pixel-shift processing software oversharpening. I was sure that Iliah Borg's PixelShift2DNG (still a free beta) would not, but, pennies being a readily available subject, I tried it. An A7RM4 was mounted on a Wild M400 with a ringlight, so that's what I used. With the ringlight undiffused there was a lot of that funky speckle false color that we now kinda sorta understand; and, with a lot of diffusion, very little, as we would expect. In both cases, the single-frame Bayer images are very, very similar to the shifted-and-merged image. Except in an A-B situation you couldn't distinguish them. In both cases, the subjective impression was that the single frame was slightly crisper, or, put another way, that the merged image could take (and needed) more sharpening.

Conclusion: here, 4-pixel shifting does no good and does no harm. The workflow doesn't amount to much: the multi-pixel shots require a single press of the release, so you could run an automated stack in just the normal way. With all the images in a folder, just point PixelShift2DNG to it, and click "Analyze + Convert All", and Iliah's little utility magically generates merged DNG's. So easy it's too bad there's no benefit in this situation. The qualification is necessary because the image is diffraction limited by the lens, not pixel-pitch limited by the sensor. (The Wild ApoZoom is a lot of fun, but the NA doesn't compete with some of today's optics -- it was intended for film.)

Lou Jost
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Re: Monochrome Camera / Techniques?

Post by Lou Jost »

Steve, I am not sure what you are doing. Are you just shifting a single whole image by one pixel in each direction?

In a real 4-image pixel-shift, the sensor is shifted so that each pixel gets a genuine measurement of each color (twice for green) of a pixel-sized point on the subject. The combining is done in the camera and can't be done with outside software. This should increase resolution. It could also include over-sharpening. In Pentax I find the jpg is over-sharpened and the RAW files are not.

iconoclastica
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Re: Monochrome Camera / Techniques?

Post by iconoclastica »

Lou Jost wrote:
Sun Sep 06, 2020 10:09 am
Wouldn't a band-pass filter in front of the lens do this trick?
No, not if you want to photograph luminance. With a narrow-band filter or monochromatic light, the only things that will be bright in the image are things of that color
The Bayer-filter itself is wide-band and responds to light beyond its favoured part of the spectrum. I don't have true monochromatic light here, nor filters that are narrow enough, so I can't test it. But unless the R and B channels are black as a result of green light, I hold it for possible.
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Lou Jost
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Re: Monochrome Camera / Techniques?

Post by Lou Jost »

I've done this with lasers, and there is crossover betrween colors, but this doesn't save you from the problem that a bright red object will appear dark under monochromatic blue light. In real monochrome photography, that area would be light (in the absence of the filters that B&W photographers are so fond of).

iconoclastica
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Re: Monochrome Camera / Techniques?

Post by iconoclastica »

Lou Jost wrote:
Sun Sep 06, 2020 11:42 am
I've done this with lasers, and there is crossover betrween colors, but this doesn't save you from the problem that a bright red object will appear dark under monochromatic blue light. In real monochrome photography, that area would be light (in the absence of the filters that B&W photographers are so fond of).
I agree, monolight gives a bit of strange appearance. However, that bright red object appears dark by absorption, so it's dark in every band and channel. Have you compared the colour channels and seen that (after scaling or curving) they would cause incomparable lightness differences?
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Re: Monochrome Camera / Techniques?

Post by rjlittlefield »

iconoclastica wrote:
Sun Sep 06, 2020 11:29 am
The Bayer-filter itself is wide-band and responds to light beyond its favoured part of the spectrum.
There is some published data that appears to be high quality, at https://nae-lab.org/~rei/research/cs/zhao/database.html .

Quickly looking through the JPG plots of RGB sensitivity for various cameras, about half of the cameras tested have no discernible overlap between R and B. The remainder do have varying degrees of overlap, so there are wavelengths where all channels are at least somewhat active. A few cameras, notably the Canon 5D, 5D Mark 2, and Kodak DCS-460, have a narrow band of wavelengths where relative RGB sensitivity reaches a uniformity around 1:5:1.

--Rik

Lou Jost
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Re: Monochrome Camera / Techniques?

Post by Lou Jost »

Have you compared the colour channels and seen that (after scaling or curving) they would cause incomparable lightness differences?
I don't think I understand the question. Since the red will appear very dark, and blue areas will be bright, the result will look nothing like a true monochrome image, where the brightness records the object's luminance (regardless of color).

Steve S
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Re: Monochrome Camera / Techniques?

Post by Steve S »

Lou Jost wrote:
Sun Sep 06, 2020 10:31 am
Steve, I am not sure what you are doing. Are you just shifting a single whole image by one pixel in each direction?

In a real 4-image pixel-shift, the sensor is shifted so that each pixel gets a genuine measurement of each color (twice for green) of a pixel-sized point on the subject. The combining is done in the camera and can't be done with outside software. This should increase resolution. It could also include over-sharpening. In Pentax I find the jpg is over-sharpened and the RAW files are not.
Sorry, I thought it was obvious from the context. The camera has a four-image shift function, so each pixel location gets the full RGGB sampling; the image is recorded as four raws, which look identical and can be used as free-standing images. Sony and Iliah Borg have utilities that convert the four images into a raw that needs no demosaicking. With Sony the combining is done outside the camera, with software. Pentax (remember Pentax? My first SLR.) is the same.

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