A good monitor will display 8 bits. But prints are limited to about 5-6
bits. And, regardless of what you might have thought, 16 bits can't
actually be seen on any device. In fact, if you feed a 16 bit image to
your monitor it's probably being converted to 8 bits on the fly.
The reason to have 16 bits is only for editing binary integers.
Whenever you reduce the brightness of a pixel its value is divided by
something. If the brightness range is only 8 bits and runs from 0-255
dividing 128 by, say, 3 yields 42.667 which (since it's integer
arithmetic) gets rounded to 43. But in 16 bit parlance the same
brightness value is 128 x 16 = 2048. Dividing 2048 by 3 yields 682.667
which (since it's still integer arithmetic) gets rounded to 683.
Although both numbers got rounded to an integer the amount of precision
lost by rounding to the nearest integer value is much smaller in the 16
bit value.
If I were to now convert 683 down to 8 bits I'd get 683/16 = 43. We end
up with exactly that same value as if we had used 8 bits to start with.
So, for a single adjustment there is no difference. However multiple
brightness, contrast, saturation, etc, etc, adjustments gradually
introduce more and more rounding errors into the 8 bit calculations.
Using 16 bit values reduces the cumulative effects of those rounding
errors which has a tendency to introduce spikes and the jaggies into
histograms.
So, forget 16 bits on the final, processed output. No one can see it...
even if you think you can. :-)
Chuck Norcutt
On 3/26/2011 12:59 PM, Jim Nichols wrote:
> Thanks for the clarification, C.H. When I save jpegs, I normally use level
> 12 in PS Elements unless the destination places a limit on file size.
>
> So, it appears that I can convert to 8-bit and do a final cleanup of my
> images without losing any quality in the displayed image. That helps me in
> my decision making.
>
> Jim Nichols
> Tullahoma, TN USA
> ----- Original Message -----
> From: "C.H.Ling"<ch_photo@xxxxxxxxxxxxx>
> To: "Olympus Camera Discussion"<olympus@xxxxxxxxxxxxxxxxx>
> Sent: Saturday, March 26, 2011 11:51 AM
> Subject: Re: [OM] IMG: Friday Tulip - Jim N.
>
>
>> Our monitor can only display 8 bit information (24 bit RGB). TIFFs are
>> mostly non compressed (and not compress very well), JPEG is compressed
>> image, some informations are lost during the compression. In many cases
>> the
>> quality loss is very little unless you use very high compression rate. I
>> use
>> level 11 in PS, I cannot distinguish its quality from TIFF.
>>
>> C.H.Ling
>>
>> ----- Original Message -----
>> From: "Jim Nichols"<jhnichols@xxxxxxxxxxxxx>
>>
>>
>>> Hi Chuck and C.H.,
>>>
>>> The images that I post are placed in the Leica Users Group (LUG) gallery,
>>> which will accept either tiff or jpeg images. The tiff image files are
>>> much
>>> larger than the jpegs, hence I concluded that they contained more
>>> details,
>>> etc. In looking at the images that I have posted recently, the tiff
>>> images
>>> "appear to me" to be of better quality. Perhaps this is just a
>>> perception
>>> that I have. For that reason, I have sometimes resisted changing them to
>>> 8-bit for final touch up.
>>>
>>> Am I mistaken? Do our monitors and prints show only what would exist in
>>> an
>>> 8-bit image? I'm not enough of a techie to know how to evaluate this.
>>>
>>> I also save all of my RAW files, so I can, and sometimes do start over
>>> when
>>> I don't like my work in post-processing.
>>>
>>> Jim Nichols
>>> Tullahoma, TN USA
>> touch pixel brightness levels
>>>>>> except for final sharpening at print resolution.
>>>>>>
>>>>>> If neither your display nor prints can show the 16-bit
>>>>>> color/luminosity
>>>>>> detail why keep it?
>>>>>>
>>>>>> Chuck Norcutt
>>>>>>
>>>>>>
>>>>>> On 3/25/2011 6:04 PM, Jim Nichols wrote:
>>>>>>> Thanks, Chuck. I have had a busy day, but saw that after I put it
>>>>>>> up.
>>>>>>> I'm
>>>>>>> torn, at times, between the need to edit, which, in my case means
>>>>>>> going
>>>>>>> to
>>>>>>> an 8-bit image, or the desire to retain more detail in a 16-bit tiff
>>>>>>> image.
>>>>>>> Lately, when I can, I have been going with the tiff.
>>>>>>>
>>>>>>> Jim Nichols
>>>>>>> Tullahoma, TN USA
>>
>> --
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>>
>
>
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