8 Bit or 16 bit , sRGB or Pro Photo

Started Sep 11, 2019 | Discussions thread
knickerhawk Veteran Member • Posts: 7,010
Re: The difference is ...

technoid wrote:

Ken60 wrote:

Ok lots of replies and comment , I too have been printing with the Pro Photo and 8 / 16 bit. Yes the differences are small , however I have one or two things I want to eliminate before drawing a final conclusion.

When many speak of a colour space they almost give it colour. It has none , it is only a container into which we place data and allow the space to define the interrelationship between that data and its use. So an empty container ....... As this space grows from sRGB to ProPhoto so with the same data content (8 bit) , the transitions must show differently to a higher, more intricately defined amount of data.

There are areas where the finer granularity of sRGB compared to ProPhoto can result in smaller dE's between a high bit RGB value and an 8 bit RGB value. The difference can be significant if the rounding of the high bit values happens at the most sensitive RGB values. Specifically:

High bit sRGB (31.51 29.49 27.51) and 8 bit (rounded) sRGB (32,29,28) Produces a dE2000 of 1.07.

ProPhoto RGB is more sensitive:

High bit ProPhoto RGB (19.49,16.51,9.49) and 8 bit (rounded) ProPhoto RGB (19,17,9) Produces a dE2000 of 2.44.

So patches of these RGB values in 8 and 16 bits, side by side, will show visible differences. For sRGB, just barely. For ProPhoto RGB, more distinctly visible. You should be able to see the differences with a good, 30 bit (3x10) monitor by creating side by side patches in Photoshop.

Virtually all pixels aren't anywhere near this bad and the noise intrinsic in a photo image, as opposed to a synthetic image, makes these anomalies invisible as they are subsumed in the dithering that naturally occurs by the printer as it spreads tiny differences over larger areas because of the limited number of inks.

But it should be clear that the workflow and especially, any editing, should be done in 16 bits. Printing photos will be fine if done in 8 bits if necessary but one should try to stay in high bit prior to that.

Nicely explained. The image below might help to illustrate what you're saying. This is constructed from screen grabs (8-bit on my iMac) of a synthetic gradient in Photoshop. The top half consists of two strips (8-bit and 16-bit) of the same gradient in ProPhoto. The bottom half consists of two strips (also 8-bit and 16-bit) of the same gradient in sRGB. Note that when viewed in Original Size, you should be able to see a visible difference in the top ProPhoto renderings due to the visible banding in the 8-bit version. Virtually no banding is visible in the 8-bit sRGB rendering compared to the 16 bit rendering. The finer "granularity" of the tonal steps in this region of the sRGB color space means less risk of tonal banding. Of course, the naturally occurring dithering effect of noise in real photos usually makes this a non-issue.

Top quarter= Prophoto 8 bit; second quarter= ProPhoto 16 bit; third quarter = sRGB 8 bit; bottom quarter = sRBB 16 bit

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