Does Photoshop really process 16-bit images as 15-bit internally?
Asked 9/4/2019
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2 answers
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I’ve seen claims that Adobe Photoshop converts 16-bit images to 15-bit internally, so a 16-bit TIFF is effectively edited with values mapped into a smaller range. Is that true, and if so, why does Photoshop do it? Does it affect saved files or image quality in practice?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
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Yes, internally Photoshop converts 16 bit tiffs to 15 bits where 0:32768 is the same range as 0:255 in 8 bits.
Adobe's Chris Cox confirms it here: https://forums.adobe.com/thread/792212
And I have verified it by creating 16 bit tiffs in Matlab and examining how Photoshop reads the.
Note that Photoshop expands it back to 16 bits when saving tiff files by expanding it to 0:65535
Doing this has no significant effect on image quality and produces a shift of less than .01 Delta E. The math is simpler, faster and Photoshop dates back to the early 90's when CPUs needed every last help in speed.
Originally by user58107. Source · Licensed CC BY-SA 4.0
user58107
6y ago
0
Generated from our catalog & community — verify before relying on it.
Yes. According to the community answer and Adobe’s Chris Cox, Photoshop has historically used a 15-bit internal representation for so-called 16-bit images, mapping roughly 0–32768 internally where 8-bit uses 0–255. When saving back to formats like TIFF, Photoshop expands the data back to the 16-bit range.
The main reason is historical performance: Photoshop’s architecture dates back to a time when simpler math and faster processing mattered a lot more on older CPUs.
In practice, this has no meaningful impact on image quality for normal photographic editing. The reported error is extremely small (less than about 0.01 Delta E), so it’s generally not visible.
From the provided answers, the claim is specifically about Photoshop, but no reliable version-by-version list or comparison with other editors is given. So the safe conclusion is: yes, Photoshop has historically done this internally, but it does not materially harm real-world image editing results.
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