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The Image Lab

As you gain experience, you will demand more control over imaging processes in your quest for the "perfect picture". The Imaging Lab lets you manipulate hidden image buffers for flexible control over combined bitmap operations. When used in conjunction with "low-level" functions, the permutations for enhancing an image are virtually unlimited.

A common problem exhibited by digital cameras and scanning devices is poor color gamut or miscalibration. If the problem is poor color gamut, the number of diverse colors in the image is limited by the camera or scanning device. In the case of miscalibration, red green and blue values are erroneously shifted towards shadows or highlights. In other cases, the problem resides with the source material -- e.g., old photographs typically degraded over time.

Note: If your display is not gamma-corrected, subtle changes may not be visible.

• Open/view before1_demo.jpg
• Select Image|Histogram (or Ctrl-H)

before1_demo	Histogram

This image has a very poor color gamut which explains its poor contrast. Moreover, the blue shades of the image are not only impoverished but skewed; this may be due to current lighting conditions, flash effects, film or camera charcteristics and/or deterioration of the film over time.

• Select Enhance|Fix_UnderExposure.
• Select Levels,_Back_Fill method.

Here we find the default value detected for adjusting highlights is adequate. Highlights slider was set to "151". Experimenting with the Gamma slider "washed" the image since contrast is very poor; adjusting midtones flooded the shadows with light. As such, we leave Gamma slider at its default position for no change. Finally, adjust the Mask slider to "25" to avoid overexposure by blending some of the original highlights and midtones. As is, the overall exposure correction can be considered done. Let us proceed to advanced smoothing and sharpening.

• Select Lab|Duplicate. (Image is copied to a hidden image buffer.)
• Select Enhance|Clean/Soften.
• Click Airbrush method.

Isolate the flesh tones. On the "Original image" pane, click a pixel on her cheek to select a flesh tone. Adjust HLS bands to select range of colors that encompass the flesh tones in the photo - selected range of colors as displayed by the purple mask. To see a preview of the smoothing effect, uncheck the "Modified image (show mask only)" box.

• Select Lab|Swap image. (Image in hidden image buffer is swapped with modified image.)
• Select Lab|Mask Edges.

The Filter and Effect sliders are adjusted such that edges and airbrushed flesh tones are combined optimally.

• Select Enhance|Details/Sharpen.
• Click Unsharp_Mask method.

Last but not the least, overall sharpness is enhanced via Unsharp Mask method.

Summary: As in previous lessons, we first apply color correction and/or exposure enhancement procedures. By manipulating image buffers you can control which picture elements are combined. In this lesson, the image's signal-to-noise ratio was enhanced by selective combinations. The number of permutations are unlimited.