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Author Topic: Scanning color negatives - best resolution?  (Read 24633 times)

Mark D Segal

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Re: Scanning color negatives - best resolution?
« Reply #40 on: January 06, 2015, 06:16:42 pm »

Yes, Alan, good suggestion - that could be workable, but would need to research how it would be attached to a Phase One camera and what accessories would be needed to fill the frame with the media at least on one dimension - can't do it for both because the aspect ratios won't match, but that's OK. Means going completely manual, perhaps best tethering the camera to a laptop, experimenting with focus and exposure till one gets it exactly right for each media size and type. No doubt doable and probably wouldn't cost the sky, except for the front-end time. The issue is how much time and money one needs to spend before knowing how worthwhile. I can surmise it may be excellent, but one doesn't know till after a fair bit of experimentation. To keep in mind!
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Mark D Segal (formerly MarkDS)
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AFairley

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Re: Scanning color negatives - best resolution?
« Reply #41 on: January 06, 2015, 08:10:51 pm »

Mark, the biggest factor in this type of thing is that what one is chasing are pretty much marginal improvements I think....
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Mark D Segal

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Re: Scanning color negatives - best resolution?
« Reply #42 on: January 06, 2015, 08:34:38 pm »

After a point, for sure. When going manual fitting manual third-party stuff on a camera never conceptualized for it, I think there's a fair bit of essential work before one gets to the point where after the improvements are marginal. To some extent this kind of thing, from what I've seen, is binary - either you get it right or you don't for some identifiable reason - and it's pretty obvious; but after it's fixed further change does become less significant. This is where (good) scanners have some advantage, in the sense that the package is pretty much fixed and you kind of know what you're getting from the get-go.
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PeterAit

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Re: Scanning color negatives - best resolution?
« Reply #43 on: January 07, 2015, 11:04:30 am »

Well, thanks to all for the many responses. I feel like the guy who asked the time and was told how to make a watch!
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Bart_van_der_Wolf

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Re: Scanning color negatives - best resolution?
« Reply #44 on: January 08, 2015, 06:08:43 am »

Well, thanks to all for the many responses. I feel like the guy who asked the time and was told how to make a watch!

Hi Peter,

I also hope you got an answer to your question that you can use ...

In fact, I've also installed the Epson Scan utility, just to verify whether the somewhat strange results I got with Vuescan are not the product of a bug or something like that. Well, Epson Scan confirmed the linear increase with scan density for the lower PPIs. up to 800 PPI, and the same sub-proportional increase for the higher PPIs from 3200 to 6400. However, where VueScan also allows 1600 PPI at double the resolution of 800 PPI, Epson scan only offers a 1200 PPI or a 2400 PPI, with the later being similar to an interpolation between VueScan's 1600 and 3200 PPI, but 1200 PPI perhaps being a bit worse than possible (see attachment). VueScan clearly extracts more resolution from the film at 1600 PPI, where Epson Scan would require 2400 PPI to slightly improve over that because it doesn't offer the 1600 PPI option.

Concluding one could say that VueScan seems to have a pivot point at 1600 PPI, and Epson scan at 800 PPI, beyond which only more sub-proportional resolution gains can be expected. Of course VueScan's 1600 PPI will produce smaller output sizes than Epson Scan's 2400 PPI that would be needed to approximately match the relative resolutions, which is useful if you want to maximize resolution at a relatively small size.

In addition, Epson Scan offers 9600 and 12800 PPI modes, but that produces virtually identical resolution to 6400 PPI, although with hugely larger files. The only use I currently see for such settings is when one does need to deliver such huge files. In that case it may (marginally) help to actually scan (by smaller stepper motor movements in the slow scan direction) the pixels instead of just interpolating them.

Do note that these measurements I made were based on 35mm filmstrips (with all the non-flatness and positioning issues that come with it), and that presumably that triggers the use of the higher resolution (6400 PPI) lens of the dual lens system. I presume that the lower resolution (4800 PPI) lens is used for a wider field of view, since the linear sensor arrays have a fixed length.

All this was a bit of a surprise to me (I never tested 35mm film strip scanning before on the V700 because I have better equipment for that), because I expected that resolution gains would gradually reduce as we approached the resolution limits dictated by the optical scanner MTF. Instead, there seems to be a pivot point where proportional resolution increases abruptly turn to sub-proportinal increases, and that at a relatively low level. This seems to indicate something mechanical (such as switching between lenses), and therefore might work out differently between actual copies of the scanners. It would be helpful if others could attempt similar measurements of e.g. a star target caught on film which allows real resolution limit quantifications.

Cheers,
Bart
« Last Edit: January 08, 2015, 06:10:16 am by BartvanderWolf »
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Alan Klein

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Re: Scanning color negatives - best resolution?
« Reply #45 on: January 08, 2015, 11:36:45 am »

Bart: So what's the best ppi to scan at on 35mm and on 120 using Epson Scan?

Bart_van_der_Wolf

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Re: Scanning color negatives - best resolution?
« Reply #46 on: January 08, 2015, 12:12:17 pm »

Bart: So what's the best ppi to scan at on 35mm and on 120 using Epson Scan?

Alan,

Best (resolution wise) is 6400 PPI (also) on Epson Scan, if you need it for the intended output size.

A compromise on Epson Scan would be 2400 PPI (extracts some 80% of available resolution), beyond which resolution can only increase a little bit while file size quadruples per full step. The difference between 2400 PPI and 6400 PPI is still significant, but only if you need it for a given output size. Higher than 6400 PPI has no significant effect on resolution.

For storage it's best to scan high and down-sample to the lowest resolution you are likely to need.

Cheers,
Bart
« Last Edit: January 08, 2015, 12:29:02 pm by BartvanderWolf »
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Mark D Segal

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Re: Scanning color negatives - best resolution?
« Reply #47 on: January 08, 2015, 01:23:06 pm »

Alan,

Best (resolution wise) is 6400 PPI (also) on Epson Scan, if you need it for the intended output size.

A compromise on Epson Scan would be 2400 PPI (extracts some 80% of available resolution), beyond which resolution can only increase a little bit while file size quadruples per full step. The difference between 2400 PPI and 6400 PPI is still significant, but only if you need it for a given output size. Higher than 6400 PPI has no significant effect on resolution.

For storage it's best to scan high and down-sample to the lowest resolution you are likely to need.

Cheers,
Bart

Higher than 6400, more than not having any effect, would probably degrade output quality because it exceeds the resolution of the sensor and triggers software making-up pixels to upres, which would show as degraded IQ if taken too far. I've been reading attentively your observations about the declining incremental improvement of resolution as the setting increases beyond 2400. If you were to actually print some of these intermediate outcomes up to 6400 your observations would be reinforced, confirming an approach to "right-size" rather than necessarily maximize - unless of course one thinks the much larger files may one day come in handy.
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Mark D Segal (formerly MarkDS)
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Bart_van_der_Wolf

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Re: Scanning color negatives - best resolution?
« Reply #48 on: January 08, 2015, 06:43:21 pm »

Higher than 6400, more than not having any effect, would probably degrade output quality because it exceeds the resolution of the sensor and triggers software making-up pixels to upres, which would show as degraded IQ if taken too far.

Hi Mark,

I'm not sure about degradation, but there will at least be no resolution increase if only interpolation is applied. There is hypothetical gain to be had if one uses the 9600 PPI stepping precision that the mechanical drive is capable of in the slow scan direction, but 6400 PPI in the fast scan direction is limited to that by hardware, the length of the sensor scan-lines. So at best there would be some asymmetrical resolution gain possible. However, it looks like it that the 9600 PPI stepping precision is used for accurate placement rather than oversampling, because I have not really seen an increase of resolution in that slow scan direction, it's just unchanged like in the fast scan resolution. More pixels yes, more resolution no.

Quote
I've been reading attentively your observations about the declining incremental improvement of resolution as the setting increases beyond 2400. If you were to actually print some of these intermediate outcomes up to 6400 your observations would be reinforced, confirming an approach to "right-size" rather than necessarily maximize - unless of course one thinks the much larger files may one day come in handy.

Well, there is an actual (although slower growing) incremental resolution available above 1600/2400 PPI. I believe that it is available as long as one doesn't exceed a total scan-area width of approx. 5.9 inches, and length of 10 inches. Wider and longer would switch to the '4800 PPI lens', to increase the Field of View that's projected on the sensor. That 6400 PPI incremental resolution means that the effects of things like grain-aliasing will also be reduced. Also the electronic and shot noise of the scanner sensor, will reduce with down-sampling, so there is a benefit to sampling at 6400 and down-sampling to the requirement (output resolution or storage size).

But I agree that one should still keep an eye on the ultimately required resolution, which is why I earlier mentioned the measured magnification potential (assuming a targeted output requirement of 5 cycles/mm), but that does require to measure the actual resolution that one's combined film+scanner MTF is capable off. My measurements of 3 different films show 3 different levels of resolution. although they do seem to be within a certain bandwidth. Maybe they were caused by different lens quality and levels of focus accuracy at shooting time, maybe it is the resolution or MTF of the film.

The measured resolution limits of 40 - 60 cycles/mm would loosely translate to 2032 - 3048 PPI real resolution, or an 8 - 12x magnification potential of the film size to output size that allows relatively close inspection.

Cheers,
Bart
« Last Edit: January 09, 2015, 06:35:24 am by BartvanderWolf »
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Phil Indeblanc

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Re: Scanning color negatives - best resolution?
« Reply #49 on: January 08, 2015, 06:48:04 pm »

And all this time I thought to scan at the highest native resolution(optical max) in the max bits your scanner can do (no software interpolation/oversampling).
3 pages later, I 'm not so sure :-)

So about that camera rig....
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Bart_van_der_Wolf

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Re: Scanning color negatives - best resolution?
« Reply #50 on: January 08, 2015, 07:00:22 pm »

And all this time I thought to scan at the highest native resolution(optical max) in the max bits your scanner can do (no software interpolation/oversampling).

Phil, nothing wrong with that. A 6400 PPI scanning density setting will actually pull out some 2032 - 3048 PPI real resolution, setting a lower scanning density will pull out less resolution. You'll pull the most resolution of what's there out of the film at 6400 PPI, and probably lose little if you then down-sample that to 75% or even 50% of the scanned dimensions for a more compact file size to archive.

Cheers,
Bart
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Alan Klein

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Re: Scanning color negatives - best resolution?
« Reply #51 on: January 08, 2015, 10:01:56 pm »

Well, I've been scanning at 2400 PPI, 48 bit, with the V600,  so I guess I'm OK for he most part.  Thanks for the input.

terrywyse

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Re: Scanning color negatives - best resolution?
« Reply #52 on: January 09, 2015, 07:12:38 pm »

Sorry if I'm a bit Johnny-come-lately.....but this is a discussion that's very near-and-dear. My friend and colleague Mark Segal directed me here as he thought I might find the discussion "interesting" based on some questions I was asking about a certain 1951 USAF target and it's real resolution.

Anyway, I've been rather immersed the past several days in finding good solid information on the resolution of various films, how this translates into scanning resolution, real detail ("system" resolution) and so on. I'm coming at this from a slightly different direction as I'm interested in how it relates to drum scanning....you see, I have a Screen 1045ai drum scanner in my office that I occasionally entertain myself with along with a gaggle of medium format gear.

What REALLY brought this to a head recently was a local photography colleague and one of the organizer's of our local Charlotte Photography Meetup Group that wanted me to try scanning a 4x5 sheet of something called ADOX CMS 20.....some sort of microfilm that's sold in sheets and 120 rolls. This film is claimed to have something like 800 lp/mm or 40,000 [cough] [gag] ppi resolution. Well, my scanner can only crank up to 8,000ppi, well under what the film is supposedly capable of.....but I assumed that the system rez (lens basically) would poop out long before we hit my scanner's top speed of 8K ppi. What I found was interesting.

One of my tests was scanning an area of small detail (fabric texture....attached) at 1K, 2K, 3K, 4K, 6K and 8K ppi. Similar to Mr. Van der Wolf's findings, I found detail improved quickly up to about 4K ppi with smaller improvements after that....but improvements nonetheless. What really surprised me was that there was real image detail improvement right up to the 8K limit of my scanner. Now, I've seen "improvements" before on my own films (Ilford Delta 100/400) but once past about 4K, it was really only improvements in grain structure, not actual image detail (side note....when I did tests of my own film, it was shot with my Pentax 645NII...I plan to do another test with my Pentax 67II to see if I can get some improved image detail at resolutions about 4K). In this case, it wasn't simply improvements in grain rendering (there WAS NONE with this film!). So either my colleague was using an excellent lens (likely) or, given the right film, lenses can perform better than I'd been led to believe (I hear numbers like 80-100 lp/mm bandied about for lenses).

Some fun facts about this drum scanner....
It has multiple discrete drum speeds that corrolate with resolution.....the higher the resolution, the slower than drum has to spin in order for the system to handle the data output. The "system" in this case is an aging Graphite PowerMac running the 90s version of OS 9.2.2! The drum speed is not stepless so there's always a transition point from one rez to another. For example, at 4000ppi drum speed is 900rpm....@ 4001ppi, it drops to 600rpm. What was interesting is that the quality slightly improves at the transition to the slower speed......at the limit of the faster speed (4000ppi) there's some grain "smearing"...but when you set the rex to 4001 and trigger the drum speed reduction, grain sharpens up. As a result, I typically only scan at 3001, 4001 and 6001 ppi resolutions.

This scanner has a 16,384 lineal pixel limit.  So, for a 4x5" sheet film, your maximum scanning rez is 16,384/5" or 3,276ppi. So, if you really need a 4x5 scanned at, say, 6,000ppi, you have to cheat by scanning the sheet in sections and stitching it later in Photoshop...works like a charm.

Scanning time.....for a 4x5" sheet @ 3000ppi, it takes nearly 90 min. to complete the scan........and for a 6000ppi scan in sections, it took me nearly 9 hours of scan time! The one saving grace is the excellent batch scanning capability of the software. You can basically batch up a drum full of scans (or sections of a 4x5) and walk away for hours....or overnight in my case.

In an interest to staying on topic and perhaps adding to the discussion, I'm more of the mind of scanning once at the highest practical resolution (typically 4001ppi) and then downsample for printing. Since it takes something like 35-45' to scan a 6x7 format, I'd rather do it just once. :)
My own personal workflow is, after development, I sleeve all my negs and scan them on my Epson V750 (yes, I have one of those too)....that becomes my contact sheet. After looking through the images, I then pick out the best (typically only 20-30% of each roll) and go through the process of wet-mounting and drum scanning.

Regards,
Terry
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Terry Wyse
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Re: Scanning color negatives - best resolution?
« Reply #53 on: January 09, 2015, 10:30:12 pm »

Terry:  Interesting process.  Can we see some of the results of both scanners?

terrywyse

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Re: Scanning color negatives - best resolution?
« Reply #54 on: January 10, 2015, 12:05:27 am »

I don't really have anything from my Epson V750 but I do have something from the drum scanner. Attached is a screen shot of several 100% views in PS ranging from 1,000 ppi (right) to 8,000 ppi (left). You can look at the filenames on the tabs for the resolution.....and see that the 8,000 ppi scan shows just a bit more detail than the 4,000 and 6,000 ppi scans. These were scans from the Adox CMS 20 film (4x5). I should note that these are with NO sharpening applied, either at the scanner or in Photoshop.

I'll see if I can come up with something from the V750 tomorrow.

Terry
« Last Edit: January 10, 2015, 12:07:04 am by terrywyse »
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Terry Wyse
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Alan Klein

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Re: Scanning color negatives - best resolution?
« Reply #55 on: January 10, 2015, 12:25:11 am »

It seems that the focus seems to degrade moving to the right where there is less resolution.  But why should that be? I can understand less resolution.  But the results on the right are also out of focus.

Do you have any examples of people and places, full photos that we can compare rather than USAF type charts.  That would be more helpful in understanding what we're looking at.

terrywyse

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Re: Scanning color negatives - best resolution?
« Reply #56 on: January 10, 2015, 01:07:23 am »

The part of the scan you're seeing is the texture of a blouse.....so it's real, not a USAF chart. I can't show the entire image since it's of a person and I haven't asked permission.

They're not out of focus. What I did was take each scan and sample them all up to 10000 ppi so they were all the same relative size. So the lower resolution scans only appear out of focus. It's difficult to show them all at the same size at their native scan resolutions.

If you'd like me to show a screen shot at their original un-sampled resolutions, I can do that.

Terry
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Terry Wyse
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Bart_van_der_Wolf

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Re: Scanning color negatives - best resolution?
« Reply #57 on: January 10, 2015, 04:29:35 am »

The part of the scan you're seeing is the texture of a blouse.....so it's real, not a USAF chart. I can't show the entire image since it's of a person and I haven't asked permission.

They're not out of focus. What I did was take each scan and sample them all up to 10000 ppi so they were all the same relative size. So the lower resolution scans only appear out of focus. It's difficult to show them all at the same size at their native scan resolutions.

Hi Terry,

Thanks for joining the discussion,and for adding your examples. The low and high contrast features of the fabric provide a useful spread of feature contrast, which would not show in the 1951 USAF chart comparisons (although there exist also low contrast versions).  It's obvious that for a fair visual comparison, one needs to scale (up) the lower sampling densities. Human vision is not that good at comparing both resolution and scale differences at the same time.

It's that difficulty of scale differences, and scanner methods, that led to the modified ISO procedures to objectively determine the Spatial Frequency Response or Modulation Transfer Function (SFR/MTF) of scanners. They more recently also included the star chart measurements in their resolution measurement methods for digital cameras, but it is hard to directly produce such a sinusoidal version with enough detail for scanners.

For us it is a bit more practical, because we need to establish a system performance of camera optics / film / scanner, which is different from looking at a scanner in isolation. For such a system performance it is very simple to take a photograph (a reduced size, and hence very high resolution copy) of such a star target which challenges even the best resolving component of the imaging chain, the camera lens. Then the combined/cascaded MTFs of all components in the system will allow to determine a rather objective metric for the limiting resolution (at a contrast level one can choose). That metric should then ideally match the required resolution goal one has for a specific use of the image.

Drum scanners typically have a spot size that can be varied, but CCD scanners usually have a fixed sensel pitch (with low fill factor) and sometimes variable lighting (ranging from collimated to diffuse) that influence the resolution (and graininess) characteristics when scanning film. But they also have that diminishing returns of resolution increase with higher sampling densities (and smaller spot sizes for more contrast), but up to some 8000 PPI it can be demonstrated that more resolution will be extracted from film, assuming the detail was captured to begin with (so low ISO, fine grained and thin emulsion, using high quality camera optics and good technique).

Cheers,
Bart
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Ray

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Re: Scanning color negatives - best resolution?
« Reply #58 on: January 11, 2015, 10:28:35 am »

Perhaps I'm missing something here. I used the Epson V700 a while back to scan some old slides and negatives, and I was rather concerned about test reports on some sites that claimed the real optical resolution of the V700 is not 6400 ppi but 2300 ppi, and that there was no point in scanning at resolutions higher than 2400 ppi. One would merely produce larger files with no increase in detail.

That didn't seem right to me. If it was true, then one could severely criticise Epson for conning the public and wasting everyone's time.

So I carried out my own tests on the sharpest of my slides and negatives, scanning the same negative twice, once at 2400 ppi and again at 6400 ppi, then compared detail, grain and resolution after appropriate processing and sharpening in Photoshop.

Now, an important principle when comparing image detail is to ensure one is comparing same size images. It's a nonsense to compare different size images. So one either interpolates the 2400 ppi scan to 6400 ppi for comparison purposes, or one downsamples the 6400 ppi image to 2400 ppi.

The results of my tests were quite clear. The 6400 ppi scans were always either noticeably sharper and more detailed, but with equal noise, or equally sharp but with lower noise.

There was no way I could get the 2400 ppi scan to match the downsampled 6400 ppi scan in its balance between noise and detail.
So my conclusion was, even if you calculate that a 2400 ppi scan is sufficient for your print size at, say 300 dpi, a 6400 ppi scan which has had more sharpening applied before downsampling, will always produce better results in terms of noise and/or detail, using the Epson V700 with 35mm film.
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Bart_van_der_Wolf

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Re: Scanning color negatives - best resolution?
« Reply #59 on: January 11, 2015, 11:01:13 am »

Perhaps I'm missing something here.

Hi Ray,

No you're not missing anything. Scaanning at a higher sampling density will allow to get more detail out of the same film, and it has a positive effect on the way that grain (or dye clouds) is rendered. However, it does take longer to scan, and the resulting file size will be larger.

Quote
There was no way I could get the 2400 ppi scan to match the downsampled 6400 ppi scan in its balance between noise and detail.
So my conclusion was, even if you calculate that a 2400 ppi scan is sufficient for your print size at, say 300 dpi, a 6400 ppi scan which has had more sharpening applied before downsampling, will always produce better results in terms of noise and/or detail, using the Epson V700 with 35mm film.

Correct, that's also what the conclusion of most other people is. One may quibble over the amount of difference that can be achieved and if it's worth the extra time and storage space, but the extra quality is there for the taking.

Cheers,
Bart
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