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Author Topic: IQ 180, or microstep-16x from an old 22mpx back?  (Read 6862 times)

TH_Alpa

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Re: IQ 180, or microstep-16x from an old 22mpx back?
« Reply #20 on: January 10, 2012, 03:42:56 am »

No harm, Theodoros.

As for your last remark, my answer would be yes, most probably, but not only (see Bart's explanation).

Best regards
Thierry

I am sorry I misunderstood you Thierry, in the begging of this conversation I thought you was saying that because of the 88mpx final image, the lens should be able to cope with 88mpx of resolution, which you didn't. I suppose you would also agree that part of the sharpness difference that Eric has noticed when comparing the 80mpx sensor with the 16x image of the 22mpx sensor, is because the lens he used found the big sensor much more demanding to cope with. Regards, Theodoros.
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fotometria gr

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Re: IQ 180, or microstep-16x from an old 22mpx back?
« Reply #21 on: January 10, 2012, 03:53:01 am »

Hi Theodoros,

Actually it is not a simple split. The physical center of the sampling position is shifted half a sensel/pixel, thus getting better response from signal that is originally best aligned in between 2 sensels. The effect is 2x higher resolution, although it is somewhat 'softened' by the half sensel overlap with its neigbors. This type of staggered sampling has a positive effect on the MTF curve and leads to reduced aliasing. The other shifts are used to sample R+G+B info at each sampling position, which also improves resolution, mostly for chromaticity and usually a little less for luminance.

All this can easily be demonstrated by taking an image of a resolution target that allows to quantify resolution, e.g. a target like the one I made available for free. See also this thread.
 
Cheers,
Bart
Hi Bart, its clear to me how it works, thanks for adding your quote, the conversation with Thierry was about how easier the method is for lenses compared with a single shot of similar resolution or one at 4x if it could be done with an 88mpx sensor. Actually if a multishot (4x) was to be done with such a sensor it would still improve sharpness in comparison to the single shot image, as you correctly imply above. Regards, Theodoros. www.fotometria.gr
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TH_Alpa

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Re: IQ 180, or microstep-16x from an old 22mpx back?
« Reply #22 on: January 10, 2012, 03:53:56 am »

Thanks Bart for the in-depth and clear explanation.

Concerning the -somewhat 'softened'- resulting image, this is very much visible when one compares the same image taken in 4-shot and in 16-shot modes.

As for the luminance resolution improving a bit less than the chromaticity one, I guess this is due to the way the information is sampled: the 2-times more GREEN pixels provide the "Luminance" information to/for the neighbor RED and BLUE pixels while each R, G and B pixel provides its own "Chrominance" information.

Is that correct Bart?

Best regards
Thierry

Hi Theodoros,

Actually it is not a simple split. The physical center of the sampling position is shifted half a sensel/pixel, thus getting better response from signal that is originally best aligned in between 2 sensels. The effect is 2x higher resolution, although it is somewhat 'softened' by the half sensel overlap with its neigbors. This type of staggered sampling has a positive effect on the MTF curve and leads to reduced aliasing. The other shifts are used to sample R+G+B info at each sampling position, which also improves resolution, mostly for chromaticity and usually a little less for luminance.

All this can easily be demonstrated by taking an image of a resolution target that allows to quantify resolution, e.g. a target like the one I made available for free. See also this thread.
 
Cheers,
Bart
« Last Edit: January 10, 2012, 04:09:01 am by TH_Alpa »
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fotometria gr

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Re: IQ 180, or microstep-16x from an old 22mpx back?
« Reply #23 on: January 10, 2012, 04:03:57 am »

Thanks Bart for the in-depth and clear explanation.

Concerning the -somewhat 'softened'- resulting image, this is very much visible when one compares the same image taken in 4-shot and in 16-shot modes.

As for the luminance resolution improving a bit less than the chromaticity one, I guess this is due to way the information is sampled: the 2-times more GREEN pixels provide the "Luminance" information to/for the neighbor RED and BLUE pixels while each R, G and B pixel provides its own "Chrominance" information.

Is that correct Bart?

Best regards
Thierry

Thierry since you was with Sinar at those days, I was wondering why they didn't apply the method to the 22mpx Dalsa sensor after Kodak seized the production of theirs, is there a technical reason for not doing so? Theodoros, www.fotometria.gr
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TH_Alpa

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Re: IQ 180, or microstep-16x from an old 22mpx back?
« Reply #24 on: January 10, 2012, 04:11:58 am »

Theodoros,

There was never the question being discussed, emphasis and development was put on newer sensors and technology.

Thierry

Thierry since you was with Sinar at those days, I was wondering why they didn't apply the method to the 22mpx Dalsa sensor after Kodak seized the production of theirs, is there a technical reason for not doing so? Theodoros, www.fotometria.gr
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Bart_van_der_Wolf

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Re: IQ 180, or microstep-16x from an old 22mpx back?
« Reply #25 on: January 10, 2012, 05:07:08 am »

Thanks Bart for the in-depth and clear explanation.

Concerning the -somewhat 'softened'- resulting image, this is very much visible when one compares the same image taken in 4-shot and in 16-shot modes.

Hi Thierry,

You're welcome. Many moons ago when I was immersed in film scanning issues, I made the following animated explanation to explain the benefits of staggered sensors (6 scan lines, 3 of which offset by half a sensel) as they were introduced by Epson. Maybe it'll help to further illustrate the principle, but then applied in multiple directions.

Quote
As for the luminance resolution improving a bit less than the chromaticity one, I guess this is due to way the information is sampled: the 2-times more GREEN pixels provide the "Luminance" information to/for the neighbor RED and BLUE pixels while each R, G and B pixel provides its own "Chrominance" information.

Is that correct Bart?

It's part of the explanation. Not only is the Green (close to Luminance) information sampled at twice as many locations as Red or Blue, but also the demosaicing makes very good use of the (lower levels) of luminance being contributed by the Red and Blue sensels. So in a way, at least some luminance is always recorded at all sampling positions. Only when there are color differences but little or no luminance differences, then the Lumnance (most important for human vision) resolution will drop (but those are rare cases). That's why Bayer CFA demosaicing works so well.

Therefore color resolution will benefit more than Luminance resolution from microstepping due to the higher sampling density of all colors. Overall resolution will benefit from the additional in-between samples.

Cheers,
Bart
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fotometria gr

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Re: IQ 180, or microstep-16x from an old 22mpx back?
« Reply #26 on: January 10, 2012, 02:49:17 pm »

Hi Thierry,

You're welcome. Many moons ago when I was immersed in film scanning issues, I made the following animated explanation to explain the benefits of staggered sensors (6 scan lines, 3 of which offset by half a sensel) as they were introduced by Epson. Maybe it'll help to further illustrate the principle, but then applied in multiple directions.

It's part of the explanation. Not only is the Green (close to Luminance) information sampled at twice as many locations as Red or Blue, but also the demosaicing makes very good use of the (lower levels) of luminance being contributed by the Red and Blue sensels. So in a way, at least some luminance is always recorded at all sampling positions. Only when there are color differences but little or no luminance differences, then the Lumnance (most important for human vision) resolution will drop (but those are rare cases). That's why Bayer CFA demosaicing works so well.

Therefore color resolution will benefit more than Luminance resolution from microstepping due to the higher sampling density of all colors. Overall resolution will benefit from the additional in-between samples.

Cheers,
Bart
Have you examined the new version of the principal, that Hasselblad applies on their 50mpx sensor Bart? I believe they increased the "step" up to 1+1/2 pixel (obviously to improve accuracy) and they make less moves now, to achieve the same result with even higher resolution. Regards, Theodoros.
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Bart_van_der_Wolf

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Re: IQ 180, or microstep-16x from an old 22mpx back?
« Reply #27 on: January 10, 2012, 06:42:38 pm »

Have you examined the new version of the principal, that Hasselblad applies on their 50mpx sensor Bart? I believe they increased the "step" up to 1+1/2 pixel (obviously to improve accuracy) and they make less moves now, to achieve the same result with even higher resolution. Regards, Theodoros.

Hi Theodoros,

According to the H4D-50MS brochure it is a 4-shot camera, so only making sure that each pixel has full color spectrum sampling. The H4D-200MS has 4-shot (50Mpix) and 6-shot (200Mpix) capability, by using a combination of 1 sensel and half sensel offsets. Maybe it's 2 additional diagonal offsets, but I'm not really sure how the sampling pattern looks.

Cheers,
Bart
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fotometria gr

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Re: IQ 180, or microstep-16x from an old 22mpx back?
« Reply #28 on: January 12, 2012, 03:18:36 pm »

Hi Theodoros,

According to the H4D-50MS brochure it is a 4-shot camera, so only making sure that each pixel has full color spectrum sampling. The H4D-200MS has 4-shot (50Mpix) and 6-shot (200Mpix) capability, by using a combination of 1 sensel and half sensel offsets. Maybe it's 2 additional diagonal offsets, but I'm not really sure how the sampling pattern looks.

Cheers,
Bart
I'am not either.., I'm looking to purchase the Kapture group 2X stitching adapter for my Fuji GX680, ...now this will be something, don't you agree? I mean an 1GB of "true color" file for a huge size painting that can be printed on 1 to 1? Regards, Theodoros. www.fotometria.gr
« Last Edit: January 12, 2012, 05:57:51 pm by fotometria gr »
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Bart_van_der_Wolf

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Re: IQ 180, or microstep-16x from an old 22mpx back?
« Reply #29 on: January 13, 2012, 06:56:15 am »

I'am not either.., I'm looking to purchase the Kapture group 2X stitching adapter for my Fuji GX680, ...now this will be something, don't you agree? I mean an 1GB of "true color" file for a huge size painting that can be printed on 1 to 1?

Hi Theodoros,

I agree it looks promising. Of course the proof is in the eating of the pudding. I don't know how precise the manufacturing of that adapter is, and if handling in practice causes a risk of unintentional changing the rear/sensor stand position. A sturdy tripod and head is warranted.

Cheers,
Bart
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fotometria gr

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Re: IQ 180, or microstep-16x from an old 22mpx back?
« Reply #30 on: January 13, 2012, 06:59:26 pm »

Hi Theodoros,

I agree it looks promising. Of course the proof is in the eating of the pudding. I don't know how precise the manufacturing of that adapter is, and if handling in practice causes a risk of unintentional changing the rear/sensor stand position. A sturdy tripod and head is warranted.

Cheers,
Bart
Oh! I am in love with my tripod, I was given a 40 years old FATIF from a retired photographer and I can have 100% success (honest I haven't missed a shot) with the "noisy" gx680 with the music at a good level from the stereo... What a tripod! In fact microstep has become as easy as a single shot now, the only difference being the exposure time. I bet you stitching will work with it. Regards, Theodoros. www.fotometria.gr
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