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  • How'd They Do That? :: River Bend

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    River Bend
    by GeneralE

    I've gotten some requests to explain in more detail how I turned this severely under-exposed shot into a "luminous" landscape.

    Resized Original: Copyrighted_Image_Reuse_Prohibited_937334.jpg Final Edited Image: Copyrighted_Image_Reuse_Prohibited_934644.jpg

    To start with, it was shot through a window from a moving train, so right off there's some motion-blur, which will have to be re-interpreted as "impressionistic" technique ... I take a lot of pictures whenever I take the train, as you get views (like this) not available any other way. However, besides the moving platform, it imposes other limitations; there's little time to adjust for lighting conditions, and creating the composition requires anticipation, timing, and reflexes -- and luck in getting the scene in focus.

    Trying to minimize the blur and keeping the noise down often results in under-exposure. Tone Curves are one of the most powerful and precise tools available for remapping tonal values to bring out detail and "correct" color. (Note: I have a common form of red-green color-blindness, so I may not see/describe colors the way everyone else does. However, I make extensive use of Photoshop's Info Window ("densitometer") to determine what the colors actually are.)

    To start with, I ran the original through an old noise-reduction program (PictureCooler), as my camera has significant noise issues. I then applied a Curve to the composite (RGB) channel. I've circled the approximate area being sampled, and the Info Window shows the Before and After tone values. Note that all adjustments are made "non-destructively" using Adjustment Layers, and can be changed or saved (exported) at any time.

    Unadjusted: Copyrighted_Image_Reuse_Prohibited_957554.jpg Overall RGB Curve: Copyrighted_Image_Reuse_Prohibited_957546.jpg Note that in the sampled area (conifer tree) the Magenta and Black values are reduced significantly, while the Cyan and Yellow values are essentially unchanged; this has the effect of making a purer green (less gray) color.

    Most of my experience is in the graphic arts/printing industry, so I prefer to view tone values as percentages of the "subtractive" colors Cyan, Magenta, Yellow, and Black -- these are the same pigments as are used whenever you print using an inkjet or color laser printer. The value on the left shows the percentage of Black if the image was converted to grayscale.

    Also note that I reverse the "direction" of the Tone Curve graph from the Photoshop default: I put the 0,0 point in the lower-left corner, with the values rising along the axes, so that dragging the Curve down lightens and pushing it up darkens the image. You do this by clicking on the little gray scale below the graph.

    In general, the "steeper" (more vertical) a section of the graph, the more detail you can bring out within that range of tones. The most common adjustment involves increasing the detail in the midtones, while allowing detail to fade or "flatten out" in the highlights and shadows, resulting in a graph which resembles an elongated capital "S" shape. In the Layers Palette you can see a thumbnail of any mask used to limit the effect of the adjustment; none in this case.

    The next step was to bring out detail in the center of the image. There are three broad zones of tones/colors: the river in the foreground, the trees, and the sky. I created a new Adjustment Layer for an RGB Curve, but first saved it without changing anything. When you create an Adjustment Layer, it automatically creates a new alpha channel: an editable grayscale channel which functions as a mask for the adjustment: it will have an effect where the mask is clear and will be blocked by the black area, and partially-applied to gray areas. I used the "Reflecting Gradient Blend" tool to create a graduated mask for the trees, but blocking the sky and river. While you have the Adjustment Layer selected, you can go to the Channels Palette and select the mask channel; you can then edit it just like any other Grayscale channel, using adjustments (Curves!) or painting/drawing tools to more precisely mask the desired areas.

    Through this graduated mask, I appled an RGB Curve. I then re-loaded the same selection and created a second Adjustment Layer using the same mask, and through this mask applied Curves to both the composite (RGB) and Blue/Yellow Channels.

    Mask: Copyrighted_Image_Reuse_Prohibited_957553.jpg RGB Curve: Copyrighted_Image_Reuse_Prohibited_957551.jpg

    Secondary RGB Curve: Copyrighted_Image_Reuse_Prohibited_957550.jpg Blue/Yellow Curve: Copyrighted_Image_Reuse_Prohibited_957547.jpg

    In the Blue channel, reducing tone values (pulling the graph down) will shift the colors towards Blue, and raising the values will shift towards Yellow (opposite from Blue on the color wheel). In this case, the lighter colors (near the bottom of the graph) are shifted towards Blue, while the darker tones are shifted towards Yellow.

    The next step was to adjust the sky and river. I took the lazy route here and just selected the inverse of the selection I'd used for the trees, made a slight adjustment, and applied another RGB Curve through that -- the same adjustment seemed to work well enough for both sky and river, so I left it at that.

    Mask: Copyrighted_Image_Reuse_Prohibited_957549.jpg RGB Curve to sky and river: Copyrighted_Image_Reuse_Prohibited_957548.jpg

    The last tweak was to try and bring out and give some definition to the hazy mountains behind the trees. For this, I made another Adjustment Layer and filled the mask with Black, then used a soft-edged brush to open up the desired areas. I then applied another RGB Curve through that mask.

    Mask: Copyrighted_Image_Reuse_Prohibited_957552.jpg RGB Curve: Copyrighted_Image_Reuse_Prohibited_957545.jpg

    As I remember now, final processing included using the UnSharp Mask filter with "high-radius" settings (e.g 15%/50 pixels diameter/zero threshold) which helps improve the apparent contrast (makes colors "pop" more), and, for the print image, adding a border and caption.


    Here are some other Before/After Comparisons using similar techniques, and most also taken from the train.

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