The effects of compressing to 8 bits

[Jamie Roberts]

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{snipped}There are incidentally quite a few people who think that the greater accuracy of the DMR actually does translate to a perceptibly better final file.

 

Mani--you're correct in theory but not, IMO, in practice. The DMR files are marginally better at low ISOs than the M8 (given a reasonable lens equivalent). At higher ISOs (like M8 640 vs DMR 800) the M8 is better, especially in the shadows, where the DMR's noise kicks in.

 

But in practice, most people print with 8 bits. There are very few printers that actually use 16 bits of data to print (and on the few that do use that, and supply plugins for PS, etc..., I've never seen a difference in print if the rest of the printing chain is properly managed).

 

After years and years of doing this, I'd even say that editing in 16bits is often over-rated, IMO, though it *can* make a difference (though probably compression schemes like JPEG vs TIFF make more of a difference in most files).

 

But for many subjects, you'd be hard-pressed to tell a difference in the final print between an 8-bit TIFF workflow (not an 8 bit capture, btw) and a 16 bit TIFF workflow--aside from bloating your hard drives.

[stunsworth]

Jamie, the 16 bits give you headroom while you're processing the image - though I expect you already know that <grin>. It's a bit like music being recorded with 24 bits even though the final output is probably going to be a 16 bit CD.

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[plasticman]

Hi guys - I'm sensing quite a lot of hostility to my posts - here and in another thread, including the implication that I don't know how to shoot competently with the camera. So I'll take this up, as I said before, with Leica directly.

 

To be honest, it's not a big problem to my shooting at the moment: mostly (if not exclusively) unimaginative child pix. But on the other hand I see no reason why the option shouldn't be available to choose compression settings that suit each person for themselves and for different circumstances.

 

As far as I'm concerned, it would just make a very good camera better.

[Jamie Roberts]

Jamie, the 16 bits give you headroom while you're processing the image - though I expect you already know that <grin>. It's a bit like music being recorded with 24 bits even though the final output is probably going to be a 16 bit CD.

 

Hey Steve--you're right of course, and if you can spare the drive space, having some head room is good. But in practice, there aren't many times shooting mainly people that the head room is necessary. So in a RAW workflow, over many thousands of shots, you certainly save time (and space) not having to go to a 16bit intermediary file.

 

If you have to do extreme editing (or have natural gradients, like blue skies), then of course 16bits for editing might be just the ticket.

 

Since I tend to do most of my extreme shifts in RAW these days, though, where I'm working with all the data I can pre-output, it makes even less sense for a 16 bit editing (not capture) workflow.

[Jamie Roberts]

{snipped}...I see no reason why the option shouldn't be available to choose compression settings that suit each person for themselves and for different circumstances.

 

As far as I'm concerned, it would just make a very good camera better.

 

Yes, it would be an improvement in terms of choice, but remember, we're talking compression schemes not ultimate bit depth.

 

When you're working with an M8 RAW, you're working with a high-bit-depth file that has lost a very little information, but it's true it's lost some. However, it's not like working with a JPEG, and the results bear it out.

 

However, with the current buffer and current cards, I'd suggest that Leica work elsewhere. The information througput would be just too slow, and I don't use continuous mode either.

 

But the DMR is very slow to write... and so is the M8 if you include a JPEG. I suspect that fully uncompressed files on the M8 would be painful.

 

Why on earth they couldn't have found a lossless compression scheme (a la Canon) and processor pipes to match, I will never, ever, know.

 

Hopefully the M9 will inherit some S2 Fujitsu goodness in the image processing area.

[carstenw]

Why on earth they couldn't have found a lossless compression scheme (a la Canon) and processor pipes to match, I will never, ever, know.

 

Jamie, I suspect that the answer is battery power. They must have had a hell of a time finding enough space for everything in the body, evidenced by the slight bloat of the dimensions which they must have known would upset the purists like myself. The unusually small battery itself is evidence of a space problem. Keeping the processing running for twice as long may not have been an option. The battery life might have dropped from 300 raws to 150, or maybe even to 100 raws+jpgs. Unacceptable.

 

Anyway, I would *still* prefer to have the option, even with the above caveat.

[t024484]

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Jamie, I suspect that the answer is battery power. They must have had a hell of a time finding enough space for everything in the body, evidenced by the slight bloat of the dimensions which they must have known would upset the purists like myself. The unusually small battery itself is evidence of a space problem. Keeping the processing running for twice as long may not have been an option. The battery life might have dropped from 300 raws to 150, or maybe even to 100 raws+jpgs. Unacceptable.

 

Anyway, I would *still* prefer to have the option, even with the above caveat.

 

The battery power is an interesting point, but may be questionable.

What can be seen in Mark Norton´s power consumption analysis, is that DNG processing and writing to SD takes roughly 2 seconds, but processing and writing JPEG's takes twice that time and twice the energy consumption.

 

Writing 16 bit DNG's would probably also take 4 seconds, just as JPEG,s.

So going to 16 bit DNG's consumes as much power as currently the shooting of JPEG's.

 

Is there any Information on how many pictures can be taken with a full battery in DNG only versus JPEG only ?

If there is no big difference between the two, the battery cannot be a reason not to write DNG's in 16 bits.

 

When looking at the picture on the M8's LCD, the picture must be read back from the SD card, (decompressed if 8 bits, nothing done if 16 bits), demosaiced, gamma corrected etc.

Nothing should be further changed here, because the LCD is no precision instument.

Reading 16 bit files takes a bit longer, so this could arguable be seen as a point on the minus side.

 

Hans

[marknorton]

The simple answer to the question Jamie claims he will "never ever know" is that Leica probably did not have the budget, skills and time required to build their own dedicated processing chip set which we're now familiar with on Canon and Nikon and will see in the S2. The M8 is built from generic parts - I can go and buy Blackfin and Renesas processors, prototyping boards, software development kits to kick start the process. Starting from a new silicon design is an entirely different endeavour.

 

If you can afford your own chip set, you can build in all sorts of hardware assists to speed the process - array multipliers, parallel processors, dedicated data compression hardware which of course make it very specific to the job at hand but very good at what it's doing.

 

As for power and body dimensions, the focal plane had to be moved forwards to avoid the DMR's LCD lump and that moved the lens mount forwards as well, by about 6mm. However, moving it that far forward would have made replicating the exact geometry of the standard M rangefinder even more difficult than it already was, so they split that 6mm - part protruding lens mount, part thicker body. That gave them more space for the battery but even so, they had to steal some of the space from the lens throat to make space for it and we know the battery would get in the way in an FF camera.

 

Going back to this image, here's the power consumption of the M8 on DMR + JPEG. From the A cursor, we have the initial release and readout from the sensor, then the JPEG write to the card, then the DNG write to the card. You can see the JPEG is the longest component - less data being written to the card but longer as the DSP struggles with those image corrections which even a decent PC takes quite a few seconds to do in C1. It shouldn't be any surprise that in-camera JPEGs are really only suitable for proofing and sending to your aunt.

 

If we did have the option to write uncompressed, it's likely the DNG part would double in width, so you certainly would not want to do JPEG at the same time; given that, I don't think the battery life would be any worse than it is now with DNG + JPEG. Finally, that residual current drain front and back, when the camera is done waiting to go to sleep. It's, say, 20% of what the camera needs when there's work to do, so you can think of the camera using up at least 1 exposure of power every minute it's idle but not sleeping. That's why I have suggested to Leica to have shorter sleep times, 10, 30, 60 seconds instead of the current minimum of 2 minutes which would allow for longer battery lives. The default equivalent on my Nikon D3x is 6 seconds.

 

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[marknorton]

When looking at the picture on the M8's LCD, the picture must be read back from the SD card, (decompressed if 8 bits, nothing done if 16 bits), demosaiced, gamma corrected etc. Nothing should be further changed here, because the LCD is no precision instument. Reading 16 bit files takes a bit longer, so this could arguable be seen as a point on the minus side.

 

Yes, it would be a lot slower when displaying an image before you get the refinded version and can zoom in. However, none of us are saying that this option would be without compromise and anyone who thought it was a problem could go back to compressed.

 

What's the display time like on a DMR?

[Jamie Roberts]

{snipped}

What's the display time like on a DMR?

 

Relatively glacial; measured in seconds. Same for zoom time. The image quality is very nice though