Addendum 1: The Step 5.2 Color Curves Transform Suggestions
Introduction:
For Step 5.2, the Color Curves transform was used to increase contrast and saturation of the masked 30->70% tone range of the image. Optimized changes to the 0->30% and 70->100% tone ranges having previously been made in Steps 3 and 4.
Form a HSV,V Smooth Curve [0,0], [15,0], [35,25], [65,80], [85,100], [100,100]:
The black point was shifted from [0,0] to [0,15] and white point was shifted from [100,100] to [85,100]. This effectively expanded the masked 30->70% tone range to 20->80%, increasing the contrast. Additionally, a slight brightening 'S' contrast curve was formed on the new diagonal line by adding two control points at [35,25] and [65,80]. This further increases the new tone range to 18->86%. Where the final HSV,V curve is below the original [0,0]->[100,100] diagonal line, the tones will be darkened. Where the curve is above the original diagonal line, the tones will be lightened.
HSV,V Curve Formation Detail. Left - black/white points changed. Right - added slightly brightening 'S'contrast curve.
Let's take a look at a temporary Img7 and check it for saturation changes effected only with the HSV,V curve change. Left is Img6's extracted saturation channel; center is Img7-HSV,V's extracted saturation channel; and right is the 'absolute difference' expanded to full tone range. The Levels & Color transform showed a 3.5% difference in the before and after saturation channels when only the suggested HSV,V curve was implemented. Ideally, there should be 0% difference as the gray tone changes, V, are at right angles to the H,S plane in the HSV inverted hexacone color space model. [Reference: Electronic Manual page 156, 'HSV Color Space']. For the extracted HSV,S channel images, black indicates 0% saturation with increasing saturations to 100% or white. For the 'absolute difference' image, black indicates 0% difference with increasing differences to 100% or white.
HSV, S Channel Comparison resulting from only the HSV,V curve change.
The Preview image resulting from the suggested HSV,V curve is improved with the added contrast but still appears somewhat 'dull'. Supplementing saturation with an HSV,S curve should further improve the image, making it more 'vivid'.
Form a HSV,S Smooth Curve [0,0], [40,45], [80,100], [100,100]:
The point at which 100% saturation occurs was relocated from [100,100] to [80,100], effectively increasing the rate of saturation change from low to medium to high and also increasing the high saturations approximately by 20%. Observing that the low saturated tones appeared unrealistic in the Preview image, a control point was added and located at [40,45] effectively establishing a curve that preserves low saturation values close to their original values [new curve and original diagonal coincide] and mildly increases mid-saturations, and highly increases high-saturations. Where the new curve is above the original diagonal, the saturations are increased.
HSV,S Curve Formation Detail.
Let's again take a look at Img7 and check it for saturation changes effected with the HSV,V and HSV,S curve changes. Left is Img6's extracted saturation channel; center is Img7-HSV,V+S's extracted saturation channel; and right is the 'absolute difference' expanded to full tone range. The Levels & Color transform showed an expected 20% difference in the before and after saturation channels when the suggested HSV,V+S curves were implemented. For the extracted HSV,S channel images, black indicates 0% saturation with increasing saturations to 100% or white. For the 'absolute difference' image, black indicates 0% difference with increasing differences to 100% or white.
HSV, S Channel Comparison resulting from the HSV,V+S curve changes.
Let's take a look at Img7's Hue, Saturation, and Value channels:
Img7 with its extracted H, S, and V channels.
A closer look at a small Img7 area:
A zoomed Img7 area with its extracted H, S, and V channels.
Note that there can be significant 100% saturation [S channel - white] but if the image brightness [V channel] has good gray tone distribution and no significant highlight clipping, the image will not appear to be over saturated.
To return to Step 5.2, click here.
You are welcome to see other IMAGEs by DEN.
