Shadow & Mid-Tone Recovery Using A Complex Tone Range Mask
Introduction:
Click on either image for medium resolution versions. . . . .Images are (c) IMAGEs by DEN 2005
The left image is a cropped [4x6 ratio] camera download image [1704x2272 pixels, 24-bit color, jpg] taken with a Canon S45 camera where the metering was set to spot and exposure set for 'exposure to the right' for the snow of the mountain. As is seen, the foreground and middle-distance image content is under exposed. Ideally, a second exposure should have been taken with better exposure of the dark image areas but a tripod was not available.
For your own trials and comparisons, 800x1200 pixel, medium resolution images for MtBaker_ori and Mask1 can be downloaded.
Step 1. Generate a 0-->60% Complex Tone Range Mask, Mask1.
Open the Mask Tool - Brightness Curve. Using the 'Probe' it was determined that the needed tone range for the mask should include the 0 to 60% tones so that the mask would exclude the mountain snow and sky. The specific complex tone range mask workflow and screenshots:
- ADD curve = [0,100], [50,100], [60,0], [100,0]; APPLY
- Blur = 50, APPLY
- SUBTRACT curve = [0,0,], [60,0], [80,100], [100,100]; APPLY
- APPLY Feather = -2
- APPLY Feather = 2
- Leave Mask Tool 'active' or click OK, creating Mask1
Mask1
Comment: While this image needed a tone range mask from 0-->60%, it may be that a range of 0-->30% or possibly 40% may be more typical for images needing their shadows and lower mid-tones masked. Use of the Mask Tool - Brightness Curve Probe will greatly help to determine the needed masking range.
Step 2. Brighten with the Subtract Filter and Mask1.
Lighten masked shadows and mid-tones with the Filter transform
Comment: Only one iteration using the Filter transform in Subtract mode was needed for this image. Other images may benefit from two or more iterations, not requiring the use of the Brightness Curve and/or Color Curves transforms of Step 3. The Composite - Subtractive Filter transform could also be used rather than the Filter transform.
Step 3. Add 15% mid-tone brightness to the resulting filtered image using Mask1.
15% added brightness to mid-tone
Comment: For this image, the Brightness Curve transform was used to further brighten the shadows and mid-tones. The Color Curves transform could have been used instead of the Brightness Curve. NOTE: The Color Curves transform is a must when changes to saturation are to be made in addition to brightness and contrast. Other images may benefit from Brightness Curve and/or Color Curves transform changes alone, without the use in combination with the Filter or Composite - Subtract Filter transforms [Filter transform use is illustrated in Step 1]. NOTE: Using the Brightness Curve and/or Color Curve [HSV,V] transforms where the mid-tone [50,50] control point is moved beyond the [50,65] coordinate point will generally result in an unacceptable 'Preview' image. If this should happen and the higher than 15% mid-tone brightening is needed, switch the curve type from SMOOTH CURVE to BROKEN LINE curve. Note: When using the Brightness Curve transform, the Probe selections must be made in the HSV or HSL color space(s) before selecting the RGB color space.
Step 4. Adjust brightness, contrast, and saturation of specific image areas.
Foreground heather is adjusted for brightness and contrast
There are a number of ways to brighten and adjust contrast and saturation of specific image areas. This is sometimes referred to as 'painting with light' [PWL]; a phrase more associated with PhotoShop image editors. One approach using PWP is creating an active mask of a specific image area and then opening either the Brightness Curve or Color Curves [used when changes in saturation are needed] transform and then using the 'color picker' to select a tone range for adjustment.
Illustrated is the Brightness Curve transform in RGB color space for increasing the brightness and contrast of the image's foreground heather. The mask is active to allow modifications if necessary without having to open/close the transform. The mask is created with the Mask Tool - Paint brush [R=50, transp=0, soft=50; brush radius is changed to accommodate needed edge inclusions] to outline the mask's edges staying inside the edge by approximately half of the brush radius; then the masked area is filled in with the Freehand Outline tool; and followed with an APPLYed Blur = the largest brush radius used. Because of the large radius Blur that is applied to the mask's edge [provides a soft gradient that prevents objectionable auras/halos], the masked area need not be exact. The Brightness Curve [or Color Curves, if used] Probe tool is used to select two points within the masked area for enhancement. Illustrated is the masked area's increase in brightness and contrast of the red hues of the foreground heather.
Additional image areas were consecutively selected, masked, and enhanced: the green hues of the right and left side trees; the brown hues of the mid-distance ridge below the snow line; and the white-gray hues of the snow and crevasses.
Step 5. Reduce noise in the shadows and lower mid-tones.
For this image, appreciable color and luminance noise resulted from the 'subtract filtering' and the Brightness Curve 'brightening'. A non-PWP noise reduced image was created where there was strong color and moderate luminance noise reductions. A 0-->20% complex tone range mask was created and the example image's 0-->20% tones where Composite - Blended with those of the noise reduced image.
Step 6. Apply various Miscellaneous Tools, touching up overall image to preferences.
Step 7. Perform needed overall image checks/changes.
These possibly include and are not necessarily limited to: full dynamic range, color balance, and sharpening.
A Special Note regarding Sharpening: because of the increased contrast and color enhancement resulting from the foregoing steps, little or no "Captive' or 'Creative' sharpening is needed. Most likely sharpening should be limited to 'Output' considerations. See: 'Captive/Creative/Output Sharpening'.
Step 1. Generate a 0-->60% Complex Tone Range Mask, Mask1, [repeat of Step 1 from Workflow1].
Open the Mask Tool - Brightness Curve. Using the 'Probe' it was determined that the needed tone range for the mask should include the 0 to 60% tones so that the mask would exclude the mountain snow and sky. The specific complex tone range mask workflow and screenshots:
- ADD curve = [0,100], [50,100], [60,0], [100,100]; APPLY
- Blur = 50, APPLY
- SUBTRACT curve = [0,0,], [60,0], [80,100], [100,100]; APPLY
- APPLY Feather = -2
- APPLY Feather = 2
- Leave Mask Tool 'active' or click OK, creating Mask1
Step 2 [new]: Using the Color Curves transform.
Click on the MtBaker_ori image and open the Color Curves transform where the Input Image = MtBaker_ori and the Input Mask = the 0-->60% tone range mask, Mask1, white = 100, black = 0 and in the HSV color space:
- Form an HSV,V SMOOTH curve = [0,0], [35,65], [70,100], [100,100]: increases brightness, saturation, and decreases contrast by relocating the 0-->60% tone range's white point to [70,100] and a +15% mid-tone increase from the resulting diagonal curve [line].
- Form an HSV,S SMOOTH curve = [0,0], [35,40], [70,100], [100,100]: decreases over saturation produced by the HSV,V curve of the lightly saturated tones while retaining the increased medium and high saturations by relocating the 0-->60% tone range's max saturation point and a -10% mid-saturation decrease from the resulting diagonal curve [line].
- Click OK, creating WF2_Step2. ['As is' this image is very similar to the final image of Workflow1].
The Color Curves transform HSV,V and HSV,S curves.
Screen shot Workflow2 Steps 1 to 2.2, just before clicking OK.
Comment: Even though the resulting image of Workflow2 Step 2 may be adequate, it is recommended that similar steps continue for this image as in Workflow1 starting with its Step 4: Specific image area enhancement; Step 5: Noise reduction of the 0-->20% shadow tones; Step 6: Preference touchup with Miscellaneous Tools; and Step 7: Overall checks and changes. A Special Note regarding Sharpening: because of the increased contrast and color enhancement resulting from the foregoing steps, little or no "Captive' or 'Creative' sharpening is needed. Most likely sharpening should be limited to 'Output' considerations. See: 'Captive/Creative/Output Sharpening'.
Question1: In your example of 'Shadow & Lower Mid-tone Recovery' you used the image to filter itself with the method set to subtract to brighten the image. I'm curious, what is the advantage of doing this versus using curves or some other method to brighten an image.
den: The currently posted workflow [will be re-named workflow1] was meant to show a more 'generic' approach that could be used where less severe recovery is needed and a more step by step process for a final image that is bright and vivid. The MtBaker image happen to be one I was working on and I used it as an example.
The advantage of using the Filter transform in either additive or subtract mode [or the Composite - Filter or Subtract Filter transform] with an image as its own filter is that you can capitalize on the image's own color/gray tones. As the transform operates, the image's pixel to pixel relationships are maintained, howbeit in a non-linear fashion. The outcome of this is that most of the time, a more realistic image results than one produced from a 'trial & error' curve manually modified with added control points in the Brightness Curve or Color Curves transform.
Many times I like to use the Filter transform because it has the added feature of Exposure Compensation... which when used in small increment adjustments adds more control over the transform's output image.
Filter transform characteristics when an image is used as it own filter: Additive: increases contrast & saturation, darkens and Subtractive: decreases contrast & saturation, brightens.
Note that the 'subtractive' characteristics are just what is needed without a lot of fuss for under-exposed image areas that are characteristically heavily contrasted, saturated, and dark.
Question2: Den, could you explain why you go into the trouble of bluring the mask edge and than feathering in and than feathering out? One idea that worked for me in the past was feathering OUT then IN as it fills pinholes in the mask... Cheers.
den: A 'tone range' mask is different than an 'image area' mask.
An 'image area' mask includes 0-->100% tones if those tones are inside the masked area boundaries, and yes, in this case 'pinholes' need to be closed using a blur and/or feather because changes are to be made to all tones contained within the masked boundary.
A properly selected and executed 'tone range' mask will effectively isolate all image areas that contain the selected tone range from all other tones that may be scattered throughout the image so holes will appear in the mask, like in the case of Mask1, the sky showing through the left and right side tree limbs and this done without needing to tediously subtract these sky areas using a mouse providing there is sufficient tone differences between the sky and the limb.
A 'tone range' mask effectively allows you to treat the masked image areas as an 'image within an image' changing the masked 'tone range' image areas', white/black points, brightness, contrast, and saturation without affecting the unmasked image areas. In the case of the MtBaker image, the sky and snowy mountain top, image area and tones, where effectively isolated from those areas and tones that needed recovery.
A 'Shadow Tone Range' mask is one that has as its starting tone, black [0%, 0 tone value] and may be generically formulated by [Mask1 range = 0-->60% tones]:
- ADD curve = [0,100], [(a-10),100], [a,0], [100,0] where the desired tone range is 0-->a%.
- Blur = at least 25-->35% of the largest approximate circle diameter that is masked [white] by the ADD curve.
- SUBTRACT curve = [0,0], [a,0], [(a+20),100], [100,100]
- APPLY Feather = -2
- APPLY Feather = 2
- Generally I prefer to leave the mask 'active' but it should also be check for 'full dynamic range'. This can be done by eye or by clicking OK and then opening the Levels & Color transform and using the 'range' feature.
For an additional discussion with edge diagrams as to why these formulation steps are necessary for proper tone range mask edges, see the DL-C message board thread HERE.
The combination of the ADD curve slope, Blur, and SUBTRACT curve slope of the Tone Mask steps are really nothing more than a large value '-Feather' action where you don't have to wait for PWP's transform to do all the calculations.... and provides a high degree of control, especially when you use an 'active' mask workflow.
The '-/+2 Feather' steps soften the pixels right at the mask edge to prevent bright, small halos similar to over applied USM halos...
The Blur radius selection... this is to a large degree 'trial and error' but you can look at this way.... assume you created a tone mask that has an approximate circular area of 100 pixels in diameter and has sharp edges that require softening... if the blur radius used is too small [r = 5] you will have a mask with strong tendencies to create halos when applied... and if the blur radius is too large [r = 100 or more], then white area of the mask becomes not white but gray, loosing its effectiveness... hence the suggestion that the blur be at least 25-->35% of the largest pixel area masked... the maximum blur is 'trial and error' that will provide the desired image changes without turning the mask's white area mostly gray.
When the Mask Tool blur is used and you have a sharp edge to blur, the result is a +/- gradient with the width of 'r' from the edge... that is why a SUBTRACT curve is need for the ADD curve and the different SUBTRACT/ADD curve slopes contribute to the different rates of change for the gradients away from a 50% gray tone on the mask's edge.
Question3: In the 3-tone range adjustment procedure instructions are to create a highlight tone mask 80-100%, and similarly, the shadow tone mask is 0-20% and the mid-tone mask is 20-80%. Do these percentages refer to the Brightness Curve grid, or do they refer to a percentage of the histogram's actual tonal range, which may not be from 0 - 100?
den: I know this begs the question but the answer is yes to both conditions. It really depends upon the image content and what enhancements are desired.
Generally though, the 3tone range procedures work best if the image already has full dynamic range, which can easily be done with the 'Levels & Color' transform before starting the masking procedures.
In the case of landscapes, sometimes the sky can gain exceptional enhancement when starting the highlight masking without full 100% white tones and expanding to 100% white in the HSL color space.
Please regard the suggested tonal mask ranges for highlights, shadows, and mid-tones as only starting points... part of the artistry here is the selection of the actual ranges suitable for your image....
Case in point... look in the TIPs section re 'Creating Beautiful Skies'... the highlight tone range to accomplish this was actually 65->100% rather than a generic 80->100%.
Click on either image for medium resolution versions. . . . .Images are (c) IMAGEs by DEN 2005
