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If .quad files hold 256 values, how can they convey 16-bit data ?

If .quad files hold 256 values, how can they convey 16-bit data ?

2016-06-05 by kenlee333@...

The .quad files I have created describe 256 values for each channel: that's 8-bit data, 8-bit precision so to speak.


How then can QTR send 16-bit data to the printer ? Are the additional values interpolated ?


With QTR, what do we mean when we say that we are printing in 16-bit mode ?


Many thanks !

Re: [QuadtoneRIP] Re: If .quad files hold 256 values, how can they convey 16-bit data ?

2016-06-05 by Roy Harrington

There are 256 points but each is a 16-bit value. Interpolation is done for all the
intermediate values.
Consider that Photoshop curves have a maximum of 14 points!
And not only that they are only 8-bit values. Interpolation does wonders.

Roy

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On Sat, Jun 4, 2016 at 11:31 PM, richard@... [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com> wrote:
If I understand it correctly, when a 16 bit image tone is between two of the 256 steps it will interpolate the correct 16-bit quad value for the 16-bit image value.

Richard Boutwell

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Posted by: richard@...
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Re: [QuadtoneRIP] If .quad files hold 256 values, how can they convey 16-bit data ?

2016-06-05 by Walker Blackwell

Exactly. The very large numbers in the .quad represent 16bit ink limits.

So it's 16bit (interpolation) x 16 (numbers) making the interpolation and working space a true 16bit space.

Best,
Walker
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On Sunday, June 5, 2016, Roy Harrington roy@... [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com> wrote:

There are 256 points but each is a 16-bit value. Interpolation is done for all the
intermediate values.
Consider that Photoshop curves have a maximum of 14 points!
And not only that they are only 8-bit values. Interpolation does wonders.

Roy


On Sat, Jun 4, 2016 at 11:31 PM, richard@... [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com> wrote:
If I understand it correctly, when a 16 bit image tone is between two of the 256 steps it will interpolate the correct 16-bit quad value for the 16-bit image value.

Richard Boutwell

------------------------------------
Posted by: richard@richardboutwell.com
------------------------------------


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Re: [QuadtoneRIP] If .quad files hold 256 values, how can they convey 16-bit data ?

2016-06-06 by kenlee333@...

Please correct me if I am wrong.

Are we confusing precision with accuracy ? We all know that we can be precise to 10 decimal places, but if our readings are only accurate to 2 decimal places, our data is only good to 2 decimal places.

It seems that we are starring out with readings from a 21-step wedge, then smoothing them out to 256 steps. At that point, the graph may be smooth, but it's still accurate to only 21 steps (less than 5-bit precision). smoothed out to 8-bit precision. Apparently the 16-bit driver subsequently interpolates that out to 16-bits.

We could interpolate it to 64 or even 128 bits precision if we liked, but that's just precision: the data is only accurate to less-than-5-bits, no ?

I scan film and presume that my 16-bit files are actually accurate to 16-bits, not just interpolated. Am I mistaken there too ?

Re: [QuadtoneRIP] If .quad files hold 256 values, how can they convey 16-bit data ?

2016-06-06 by Roy Harrington



On Mon, Jun 6, 2016 at 9:45 AM, kenlee333@... [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com> wrote:

Please correct me if I am wrong.

You are mixing up various issues. And worrying about things that are not important.


Are we confusing precision with accuracy ? We all know that we can be precise to 10 decimal places, but if our readings are only accurate to 2 decimal places, our data is only good to 2 decimal places.

Yeah, but accuracy is not the important thing.

It seems that we are starring out with readings from a 21-step wedge, then smoothing them out to 256 steps. At that point, the graph may be smooth, but it's still accurate to only 21 steps (less than 5-bit precision). smoothed out to 8-bit precision. Apparently the 16-bit driver subsequently interpolates that out to 16-bits.

The 21steps are on the x-axis but the y-axis is what counts for how much ink gets output.

We could interpolate it to 64 or even 128 bits precision if we liked, but that's just precision: the data is only accurate to less-than-5-bits, no ?

Data accuracy is how good your device is -- decimal places of the measured values.
Not how many patches you measured.

I scan film and presume that my 16-bit files are actually accurate to 16-bits, not just interpolated. Am I mistaken there too ?

Lots of luck there. Film is just chunks of opaque silver or clear plastic. There's no where near
16-bits of ACCURACY. But averaging over larger patches produces perception of smoothness.

The important part of printing is smooth transitions all along -- 16-bit is actually overkill,
but it insures smoothness no matter how steep or flat your gradients are.

For each location (x,y) the printer either prints a dot of ink or not -- just 1 bit. For the most part
averaging noise dominates what you see.

Roy






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