I have been frustrated by the fact that there is not really any good way of working with s-log2/s-gamut with Adobe software. So far I have not been able to find any way of working with default PP7 other than look luts, like Impulz. The problem is that I don't always want to use a look lut and I have found that the luts from Impulz don't seem to work that well with footage from the A7s anyway. The colors always seem off no matter what I had tried and grading without luts was even more problematic.
So I have worked out a way to convert s-log2/s-gamut to Rec709 without any look luts. So far the results have been good but I have not had any time to shoot with our A7s myself so I have been using stills generously uploaded by Roman Legion on vimeo. So here it goes, it is two effects that must be done in this order.
First I have attached a lut to correct the s-log2 gamma curve to rec709. This is based off a formula I found from sony for its s-log2 curve. Took some tweaking but mainly just had to deal with using video levels instead of full range. It is a 1D lut so it only affects luma. Apply this lut using a lumetri/apply color lut effect.
This is a matrix transformation from s-gamut to sRGB we will use it to fix the colors next.
S-Gamut to sRGB
1.87785101 -0.79411894 -0.08373153
-0.1768095 1.35097992 -0.17417008
-0.02620544 -0.14844233 1.17464781
Now apply a channel mixer effect and enter the follows values. The channel mixer effect appears to only allow integer values from -200 to 200 but it seems to still work fine. So you can enter them like this in the following format, what out for the const fields and leave them at 0.
Red-Red Red-Green Red-Blue
Green-Red Green-Green Green-Blue
Blue-Red Blue-Green Blue-Blue
188 -79 -8
-18 135 -17
-3 -15 117
That is it, so far this looks really promising but would like to hear how it works out for the rest of you. I am adding some corrected still from Roman Legion as well. These images are ungraded I only converted to Rec709 and adjusted exposure as they were under exposed a little.
So I have worked out a way to convert s-log2/s-gamut to Rec709 without any look luts. So far the results have been good but I have not had any time to shoot with our A7s myself so I have been using stills generously uploaded by Roman Legion on vimeo. So here it goes, it is two effects that must be done in this order.
First I have attached a lut to correct the s-log2 gamma curve to rec709. This is based off a formula I found from sony for its s-log2 curve. Took some tweaking but mainly just had to deal with using video levels instead of full range. It is a 1D lut so it only affects luma. Apply this lut using a lumetri/apply color lut effect.
This is a matrix transformation from s-gamut to sRGB we will use it to fix the colors next.
S-Gamut to sRGB
1.87785101 -0.79411894 -0.08373153
-0.1768095 1.35097992 -0.17417008
-0.02620544 -0.14844233 1.17464781
Now apply a channel mixer effect and enter the follows values. The channel mixer effect appears to only allow integer values from -200 to 200 but it seems to still work fine. So you can enter them like this in the following format, what out for the const fields and leave them at 0.
Red-Red Red-Green Red-Blue
Green-Red Green-Green Green-Blue
Blue-Red Blue-Green Blue-Blue
188 -79 -8
-18 135 -17
-3 -15 117
That is it, so far this looks really promising but would like to hear how it works out for the rest of you. I am adding some corrected still from Roman Legion as well. These images are ungraded I only converted to Rec709 and adjusted exposure as they were under exposed a little.
