8 bit vs. 16 bit joe sukenick digiquest

8 BIT 8 BIT VS. 16 BITVS. 16 BIT

Joe Sukenick

DigiQuest

www.DigiQuestPC.com

My photo lab requires 8 bit JPEG images sized for printing at 300 PPI for all prints.

Why should I take the extra time to work with 16 bit images and fill up my hard drive twice as fast?

The simple answer is…..

If you are happy with the quality of your prints you are delivering to your clients, and your clients are happy with the quality of your work, it’s probably not worth the effort.

But, if you sometimes look at your work and wish the quality of the print was better with less noise, better continuous tones, and a little more of the “film like” look….

Editing in 16 bit may help.

8 bit RGB (Red, Green, and Blue) images use the numbers from 0 to 255 to represent each of the three colors in the Red, Green and Blue channels for the image.

Zero is the absence of that color and 255 represents the maximum amount of that color.

A value of (255,0,0) is pure Red with no contribution from Green or Blue, (0,255,0) would be pure Green, (0,0,0) is pure black and (255,255,255) is pure White.

From 0 through 255 we get 256 different values that each of these three color channels can have.

If we multiply 256 X 256 X 256, we get 16.7 million combinations of colors.

This does not sound like a problem!

When we edit an image, nearly everything we do causes some data loss. If an image is underexposed and has low contrast, the histogram may only run from 25 to 225.

We open the image in Photoshop, adjust the Levels to stretch the dynamic range of the image to something close to 0 to 255 to give us dark shadows and bright highlights.

We immediately see a difference in the “pop” or “snap” of the image. The dynamic range has expanded and the image has “come alive”.

Any adjustment that affects the tonal range or contrast will cause data loss.

The magnitude of the adjustment will determine how much data is lost.

The continuous tone gradients in our original image are no longer smooth.

Result = “banding” or posterization”.

The dynamic range was expanded, but there was no data to represent the values in the vertical white areas.

The histogram on the right shows data loss in the histogram known as “combing”.

Notice the abrupt color transitions that result in the sky for an 8 bit edit.

The same sky and the same adjustments edited in 16 bit mode.

Why the difference?

16-bit images have 65,536 values for each color channel instead of 256

65,536 X 65,536 X 65,536 = 381 Trillion colors, shades and hues instead of 16.7 Million in 8 bit.

RED GREEN BLUE

With 16 bit images it would appear that we will get more dynamic range out of our images since we go from 256 shades of a color to over 65,000.

This should give us brighter whites, darker blacks, more shadow and highlight detail with colors that contain even more saturation.

Unfortunately, this is not how it works.

The extra values represent additional accuracy.

It does NOT give us more dynamic range.

We now have 255 additional values that fall betweenbetween each of our earlier 256 values in the 8 bit file.

Our 16 bit edits will still lose some data. But because we have more data than we need, when we convert back to 8 bit we do not see significant quality loss.

This extra data we now have “fills in the blanks” as we make adjustments and allows our continuous tones to remain smooth.

QUESTIONS

If I have an 8 bit image and want to adjust it, will converting it to 16 bit, and then do the editing help me?

QUESTIONS

If I have an 8 bit image and want to adjust it, will converting it to 16 bit, and then do the editing help?

Yes, if significant editing is needed, it will help.

QUESTIONS

Is it really worth the extra time to process, along with the increased hard drive space it takes to store 16 bit images?

QUESTIONS

Is it really worth the extra time to process, along with the increased hard drive space it takes to store 16 bit images?

If you want the absolute best quality, this is one step toward that end result.

Only YOU can decide!

Considerations for editing in 16 bit…

* When exposure, curves, or levels must be adjusted beyond a minor tweak

The greater the adjustment, the more risk of image degradation and the more benefit you will see with 16 bit.


* When printing enlargements

The larger the print size, the greater the quality improvement becomes


* At higher ISO's to minimize digital noise.

16 bit will effectively minimize digital noise in the shadow areas when correcting gross exposure problems.


* When you are seeing banding or posterization in your prints


* If you look at prints worked-up in 16 bit and they look better than the 8 bit ones


* When you are running out of hard drive space

16 bit images are twice as large and take up twice as much space as 8 bit images.


* If your time is limited

16 bit images take longer to process than 8 bit images because of their increased size


* When you shoot a series of shots like First Communion or all the Little League players at home plate holding a bat

If you get the exposure close and you will not be printing larger than a 5 X 7, 16 bit may not be worth the trouble.


* When you produce fine art prints and want the absolute best quality available for those prints


* If you work with Grayscale images

Grayscale images are limited to 256 levels of gray values! You do not have the additional color channel information that can sometimes mask the problems in 8 bit edits.

Additional Information

Any digital image with a bit depth over 8, when opened in Photoshop will be converted and opened as a 16 bit image.

CONCLUSION

Working in 16 bit has definite advantages when producing the highest quality work is important.

With today’s faster computers, larger hard drives, and Photoshop’s ability to allow almost all editing to be done in 16 bit, there is no reason not to work in 16 bit.

One Final Thought…

Photoshop CS3 converts images to 32 bit when processing with their “HDR” (High Dynamic Range) feature.

This allows far greater levels of smooth tonality and more detail retention from the highlights and shadows than is possible with 8 bit or 16 bit images.

You may draw your own conclusions about the merits of working in higher bit rates.

8 BIT 8 BIT VS. 16 BITVS. 16 BIT

Joe Sukenick

DigiQuest

www.DigiQuestPC.com

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8 bit vs. 16 bit joe sukenick digiquest

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