calzone
03-09-2009, 09:27 AM
I'm about to embark on calibration of my KRP500A using i1 display2 and HCFR. Have experience of calibrating before with my Samsung 40A786 LCD (excellent CMS, not so great greyscale/gamma tools) - at the time I was following the "greyscale for dummies" guide from the curtpalme website, which is a good beginners guide, but I think lacks some of the more fundamental advice that is present here and in the AVSForum. I probably floundered a bit using trial and error rather than using a logical approach as a result.
I will be using the workflow recommended on this forum for the pioneers. In an effort to try and avoid making too many errors I have a few questions those of you with expertise might be able to help out on..... Apologies if its too many, hopefully they’re not too dumb.
1. When setting the contrast the guides suggest choosing a setting just under the point where whites clip using a test pattern. Generally in Pure mode the suggestion seems to be that this is around 40 or so, but most people seem to pick a setting below this. Presumably this is done to suit people’s preference for max brightness according to their room/ambient light etc. But does it mean the top end whites are displayed “wrong” if this is below the clipping point? And does this affect the screen’s gamma? If “average” gamma is a function of the ratio between brightness from min black to max white, isn’t the total gamma across the whole range determined by these two settings (contr+brightness) only?
2. If your greyscale is quite bad before you start, does it affect the setting you would probably end up with for max contrast and brightness? I ask because greyscale is (as I understand it) the relative mix of the primary colours for each level of total luminance for the colour white. But I also remember reading that green is mostly responsible for luminance perception – if your greyscale has a low level of green relative to blue/red at 90-100IRE, will your overall max luminance be lower or will it affect the point you see white clipping?
3. Seems the pioneer CMS affects greyscale accuracy – does it work the other way round too? Also, if in normal viewing it appears the set has a slight green tint, is this more likely to be due to too much green in the greyscale rather than inaccurate or over saturated green primary?
4. When calibrating greyscale, the Dummies guide recommends tweaking the gains and offsets to get it right at 30IRE and 80IRE. Is this the best compromise in people’s experience? Anyone have better results at 20IRE or 90IRE? Is it better to get 80-100IRE spot on and worry less about 50-70IRE? I guess at 20IRE you run into the sensor’s limitations.
5. What do people do to tweak greyscale? Do you look at the plot of R, G and B (with dE below) vs IRE and tweak red or blue up and down to get it flat? Is this plot showing the slope of the luminance curves for each colour? Can you use the RGB luminance plot to work out whether to reduce or increase red or blue or is it giving you the same information as the first plot (i.e. if red is above the target gamma at high IRE, reduce the red gain). To what extent should you pay attention to Y values (as in xyY)?
6. What do the pioneer’s ISF 9pt gamma controls actually do? Do they shift gamma up/down for the point in question (and to a lesser extent gamma points close by), or do they change the luminance (presumably they must change the luminance of the curve at some point?). If you change the gamma at any point, there must be a knock on effect right throughout the greyscale – the maximum luminance at 100IRE must also change? Is this why the general consensus is to change all of them or none, and not take a piecemeal approach?
Cheers, Calzone
I will be using the workflow recommended on this forum for the pioneers. In an effort to try and avoid making too many errors I have a few questions those of you with expertise might be able to help out on..... Apologies if its too many, hopefully they’re not too dumb.
1. When setting the contrast the guides suggest choosing a setting just under the point where whites clip using a test pattern. Generally in Pure mode the suggestion seems to be that this is around 40 or so, but most people seem to pick a setting below this. Presumably this is done to suit people’s preference for max brightness according to their room/ambient light etc. But does it mean the top end whites are displayed “wrong” if this is below the clipping point? And does this affect the screen’s gamma? If “average” gamma is a function of the ratio between brightness from min black to max white, isn’t the total gamma across the whole range determined by these two settings (contr+brightness) only?
2. If your greyscale is quite bad before you start, does it affect the setting you would probably end up with for max contrast and brightness? I ask because greyscale is (as I understand it) the relative mix of the primary colours for each level of total luminance for the colour white. But I also remember reading that green is mostly responsible for luminance perception – if your greyscale has a low level of green relative to blue/red at 90-100IRE, will your overall max luminance be lower or will it affect the point you see white clipping?
3. Seems the pioneer CMS affects greyscale accuracy – does it work the other way round too? Also, if in normal viewing it appears the set has a slight green tint, is this more likely to be due to too much green in the greyscale rather than inaccurate or over saturated green primary?
4. When calibrating greyscale, the Dummies guide recommends tweaking the gains and offsets to get it right at 30IRE and 80IRE. Is this the best compromise in people’s experience? Anyone have better results at 20IRE or 90IRE? Is it better to get 80-100IRE spot on and worry less about 50-70IRE? I guess at 20IRE you run into the sensor’s limitations.
5. What do people do to tweak greyscale? Do you look at the plot of R, G and B (with dE below) vs IRE and tweak red or blue up and down to get it flat? Is this plot showing the slope of the luminance curves for each colour? Can you use the RGB luminance plot to work out whether to reduce or increase red or blue or is it giving you the same information as the first plot (i.e. if red is above the target gamma at high IRE, reduce the red gain). To what extent should you pay attention to Y values (as in xyY)?
6. What do the pioneer’s ISF 9pt gamma controls actually do? Do they shift gamma up/down for the point in question (and to a lesser extent gamma points close by), or do they change the luminance (presumably they must change the luminance of the curve at some point?). If you change the gamma at any point, there must be a knock on effect right throughout the greyscale – the maximum luminance at 100IRE must also change? Is this why the general consensus is to change all of them or none, and not take a piecemeal approach?
Cheers, Calzone