5

Let's say I have a monitor (8bit colour depth) that covers 100% AdobeRGB. Now I want to work on photos in sRGB for whatever reason. Will the monitor show in sRGB application more granular colour steps since it still can quantize the smaller colour of sRGB with 8bit resolution? Or will the absolute colour depth stay the same meaning the effective colour depth in sRGB will decrease to somewhat below 8bit?

Edit: This question is about the actual image on the screen as I would see it. Banding in the exported image shouldn't be affected by the displays gamut.

I hope I could make my point. If you need any further explaination please let me know.

Thanks in advance! Rummelbooz

  • More banding on your monitor as you are editing? Or in the image that is ultimately exported? Related: switched to RAW and seeing ugly light bands in Lightroom and Why am I am seeing rings (banding) instead of smooth graduation in my sunrise pictures? – Michael C Aug 11 at 17:47
  • I'm refering to what I see on display. As Steven Kersting pointed out, for the final image file the math of the software and so on will be decisive. – Rummelbooz Aug 12 at 10:23
  • and thus my question. Your question does not make at all clear whether you were asking about the former or the latter. Both answers (correctly) guessed that you meant the former. Neither would be applicable to your question if you had meant the latter. – Michael C Aug 13 at 1:57
  • I thought "Will the monitor show ..." would make clear that I'm asking about t he actual image on the screen. The next time I will try to be more clear. – Rummelbooz Aug 13 at 5:46
  • That's just it, though. What you see while editing is usually not "the actual image". – Michael C Aug 13 at 17:22
4

This is a valid concern.

My understanding of your question is that it's a monitoring problem rather than editing problem. That is, when you are editing an sRGB photo, you specify that your current worskpace is sRGB, instead of converting it to AdobeRGB first. In this case, all your editing is happening with full 8 bits (or 16/32 if you select so in the editor) per channel dedicated to sRGB, and you have no losses there.

However, there is still a problem of how to display the result. The chain Editor Output → OS (incl. video driver) → Display. The perfect (formal) accuracy of your editing may be compromised if this chain is 8 bit - and it usually is.

Say, for simplicity, your image has a perfect sRGB green G=255. If your display was a perfect narrow gamut sRGB, the system would eventually send this G=255 to the screen. But an AdobeRGB display can show a greener green, so your G=255 must be converted to something like G=240 for AdobeRGB. I just made the numbers up, but it is evident that you will see fewer gradient steps from 0.

In other words, conversion sRGB → AdobeRGB (or more accurately, sRGB → wide gamut display) is still happening, but past the editor in real time. The OS/driver may be handling the conversion with higher accuracy in floating point, but if there is any one place which requires 8 bit (say, as it often happens, the display itself), you will still have losses and more banding.

To eliminate the problem, the whole output chain must support higher-bit output (in practice, 10 bit). Most modern video cards support 10 bit, but it's never turned on by default. It needs to be turned on manually in the driver settings, but it's not enough. Obviously, the display must support this mode: otherwise you won't see anything. Yet it's still not enough. It's often forgotten that the application also must support it. Photoshop has a special setting to enable 10-bit output. So, this requires quite a bit of compatibility.

The question is: is 8 bit really not enough? will you see it?

My experience is this: no, the degradation is not much noticeable (even on gradients), but only for displays that do colour correction themselves with higher-bit LUTs (often 12-14-16 bit), i.e. professional displays, or if you don't do colour correction at all.

The point is: it is the colour correction that often looks bad with significant banding (esp. on grey gradients), if done in 8 bit. The reason, as I understand, is that the correction curves for each of the three channels are not identical (almost by definition). Differences in quantisation at each point cause colur shifts, and this is much more noticeable than a missing band.

Consumer monitors are calibrated and corrected by the OS or a dedicated software, and the correction is happening in the OS/Driver link of the output chain. Consequently, this usually happens in 8 bits. Professional monitors want the OS to output the plain uncorrected (but still converted to the gamut!) colours, and then correct them to the proper greys with higher quality themselves. This is a big difference. Compared to it, the additional banding due to the grey-neutral sRGB → AdobeRGB 8-bit conversion is negligible.

| improve this answer | |
  • Thank you really much for that super detailed answer. And all your arguments seem totaly comprehensible to me. The "non-linearity" of the different channels is a point I did not yet take into account. One more question related to that aspect. If I provide a monitor profile measured with a calorimeter to the OS, will this aspect be solved? The profile should handle that issue, shouldn't it? – Rummelbooz Aug 12 at 10:29
  • @Rummelbooz, it's a bit complicated issue in itself (which I'm sure is covered in some other questions). Fundamentally, when you do monitor profiling with a colorimeter, you do two very distinct things: 1) describe the actual display gamut and provide this info to the OS as a 'monitor profile'; 2) correct non-linearities of colour response of the monitor. This latter can be done by the video card or by the (professional) monitor. Doing it in 8 bits (i.e. by video cards in practice) almost invariably produces noticeable banding; the amount depends on the display characteristics. – Zeus Aug 13 at 0:41
  • It is possible to disable this correction (in the OS or in the software that manages the colorimeter) yet keep the monitor profile active. This will still allow the OS/editor to convert the colors to the monitor gamut, giving correct overall saturation and color clipping (which is quite important when working with wide-gamut displays), but may shift colors. However, if the display is 'naturally' good and has white balance close to the target (e.g. 6500K), either natively or by its internal settings, this may make sense for some tasks: it will eliminate banding at a cost of some color accuracy. – Zeus Aug 13 at 1:03
  • The closer the monitor is brought to proper calibration using the monitor's controls before the profile is created, so that the correction differences derived from the profile will be much less from each channel to the others, the less banding there usually is. – Michael C Aug 13 at 2:03
  • Zeus and MichaelC thank you two for your explanations. That really helps me a lot! – Rummelbooz Aug 13 at 6:00
2

The actual problem occurs due to the accuracy of the math (editing bit depth) and not the color space itself. I.e. you can edit in sRGB with 16 or 32 bit accuracy in photoshop and (largely) avoid the 8bit banding issue.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.