IMG_0025_gamma_2-2.jpg   . . .a MM Image. . .
...A RGB Brightness Curve with Mask Approach...

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RGB Brightness Curve Applied with a mask plus 'sun-dappling - Version4' . . .   . . .a MM image...used with permission. . .
". . .It was made from the roof of the Galleries Lafayette in Paris looking at the rear facade of the Opera. . ."

MM's down-sized original image, IMG_0025_gamma_2-2.jpg, is a 799x1200 pixel, [warning] 400 KB image file derived from a Canon Rebel XT [EOS-350D] CR2 [RAW] file converted to a tiff working file using PWP4x converter features.   The converted working file was re-sized using the default bi-cubic method settings and then saved as a *.jpg file at 100% quality.   Specific PWP4x conversion settings:
  • Camera make and model: Canon EOS 350D Digital;
  • Gamma: 2.2;
  • Contrast: No expansion;
  • Color profile: Canon Digital Rebel XT (0509wg22);
  • White point: Camera WP;
  • Color space: sRGB; and
  • Preferred interpolation: AHD
Additional discussion regarding this image may be found here [HSL and HSV Color Curves applications] and here[RGB Brightness Curve application to various RAW conversion gamma settings] on the DL-C message board.

The HSL and HSV Color Curves approaches with illustrations are located here.   Both of these suggested color spaces produced images that lacked 'warmth' in the shadows and lower mid-tones colors [saturation/hue].

In the following workflow, the gamma = 2.2 RAW conversion file was selected only because the shadows and mid-tones were less compressed than either of the gamma = 1.0 or gamma = 1.4 conversion files.   Similar results can be obtained with any of the message board [here] varying gamma RAW file conversion illustrations.

IMG_0025_gamma_2.2.jpg [a 100% quality jpg, resized to 799x1200 pixel, [warning] 400KB file of a Canon CR2, 2304x3456 pixel, RAW conversion to tiff file] has two image areas of interest, the buildings and sky/clouds.   This shows in the histogram with two peaks, a lower tone range peak for the buildings and an upper tone range peak for the sky/clouds.   As the buildings are of main interest, the sky/clouds are masked from the aggressive changes to brightness, contrast, and saturation that are needed to bring the buildings to acceptable levels.   Without the mask, the sky/cloud image area detail will be severely lost.   Although this image was derived from a RAW conversion file, it could also so easily be an image that was a jpg camera download image where 'expose to the right' exposure considerations were made with the camera settings such that the sky/cloud brightest spots would just be clipped.   This type of consideration generally produces an image where the shadows and lower mid-tones need 'recovery'.

Workflow Summary:   A soft gradient transition mask separating the sky/clouds and buildings was formed using the Mask Tool – Brightness Curve in ‘Stair Step’ and ‘Log Histogram’ [or ‘High Resolution Histogram’ for PWP3.5/4.0] to locate the histogram dip between the sky/clouds and buildings; Add – Apply the determined ‘Stair Step’ curve; Apply Blur = 35->50; and then leave the mask active on the RAW converted working file.   Click on the working file image and open the Brightness Curve transform and in the RGB color space form a curve and adjust mask white/black amounts to preference while monitoring the results in the Preview window.   A 'sun-dappling' effect was then performed on the resulting RGB Brightness Curve transformed image version followed with AdvanceSharpening.

Step1:   With the RGB Brightness Curve transform and a mask separating the building and sky/cloud image areas, apply a brightening 'S'-contrast curve, click OK, creating Img1.
  • Add - APPLY with the Mask Tool - Brightness Curve, Step.crv to IMG_0025_gamma_2-2.jpg;
  • Blur = 50, APPLY leaving the Mask Tool active on IMG_0025_gamma_2-2.jpg; and
  • Click on IMG_0025_gamma_2-2.jpg and open the Brightness Curve transform selecting the RGB color space, form a RGB.crv, click OK, creating Img1.
Addendum 1: Step1 in more Detail
Download IMG_0025_gamma_2.2.jpg

Step1
  Open or click on IMG_0025_gamma_2-2.jpg and open the Mask Tool - Brightness Curve.
      Form a mask Step curve = [0,0], [53,0], [53,100], [100,100] (Step.crv) and Add and lower left             Apply.
      Set Blur = 50 and lower left Apply.
  Click on IMG_0025_gamma_2-2.jpg and open the Brightness Curve transform.
      Set the Color Space = RGB.
      Form a Smooth curve = [0,0], [7,0], [20,15], [51,75], [100,100] (RGB.crv).
      Set active Mask amounts: white = 25% and black = 100%.
      Click OK creating Img1.
  Close the Mask Tool.

This completes Step1 and you should be able to closely reproduce the Screen View illustrations 1a, 1b, and 1c and Img1.   If help is needed with any of the Mask Tool buttons or Brightness Curve buttons, press keyboard 'F1' after clicking on or opening the pertinent dialog box.

Note: the above curves and settings are specific to IMG_0025_gamma_2-2.jpg and may not be universally applicable.

Nuance:   Setting the curve black and white points with the RGB Brightness Curve set to 'High Expansion Histogram' from the OPT drop-downs will ensure maximum image data retention, i.e., no R, G, or B channel clipping.   In this case, the black point was set in this manner, [0,0]->[7,0], and the white point was already [100,100] so there is some slight highlight clipping present.



Screen View 1a



Screen View 1b



Screen View 1c


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RGB Brightness Curve Applied with a mask, Img1 . . .   . . .a MM image...used with permission. . .
Comments:
  • The 'transition mask' acts as a virtual Neutral Density Filter where the Blur and the White/Black amounts simulate the differing filter densities;
  • Adjust the Blur and the White/Black amounts to provide acceptable gradients from the median tone that separates the buildings and sky/cloud tone ranges, i.e. from the low point tone [53%] between the histogram peaks, so that obvious halos/auras are not generated;
  • Initial changes made in the RGB color space may be more expedient and simpler as color [saturation/hue] will change with tone, keeping the relationships as recorded by a camera's sensor than perhaps in PWP's default HSV or HSL color spaces where color [saturation/hue] often requires a separate and additional curve;
  • Subsequent changes to preferences may be best performed in PWP's default HSV and/or HSL color spaces; and
  • Step1 Summary: the RGB curve applied to IMG_0025_gamma_2-2.jpg expanded the original buildings image area tone range of 7.5 -> 53% to 0 ->74.5% with a brightening 'S'-Contrast curve.   The sky/cloud image area detail/contrast loss was limited to preference through a transition mask that identified the image's 53% tone value image areas [the lowest point between the two histogram peaks] with added Blur = 50 gradients.

Step2:   Perform the 'Sun-Dappling' effect on Img1 to create a preferred image Version4.
Comments:
  • 'Sun-Dappling' [a PWP3.1.h workflow carry over] is a technique used with either a hand painted mask or an image area mask generally combined in Overlap mode with a high contrast mask curve of the image area highlights and PWP's Filter transform;
  • A first application to brighten highlights is made with a 'warming' solid Additive filter color [usually RGB = 100, 98, 90] with ExposureCompensation = 10 and mask white = usually 38->100, mask black = 0; while checking with the Readout Tool and a zoomed Preview to make sure there is not too much loss of highlight detail [clipping];
  • This is followed by a second application on the resulting image to slightly increase contrast and saturation of the shadows and mid-tones.   The first application resulting image is filtered with itself in Additive mode with ExposureCompensation = 0 and mask white = 0, mask black = usually 7.5->12.5;
  • 'Sun-Dappling' with a hand painted mask is illustrated here;
  • With an image area mask combined in Subtract mode with a high contrast mask curve is illustrated here; and
  • The 'dappling mask' used with PWP3.5/4.x's Soft Light or Hard Light filters could also be used but would not add warm toning which may be desired to emphasize or create an early/late daylight ambience.
For Img1, an image area mask of the image's buildings area was created and then 'Overlap - Apply-ed' with a high contrast Brightness Curve.   This mask with preferential white/black amounts was used with the Filter transform as described above to create a preferred image version that was AdvancedSharpened to become Version4.


Screen View 2a



Screen View 2b



Screen View 3


Preferred Version4:

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RGB Brightness Curve Applied with a mask plus 'sun-dappling - Version4' . . .   . . .a MM image...used with permission. . .


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Last Update: 070228 Rev3 revised Addendum1           (c) IMAGEs by DEN 2006   All Rights Reserved