April 2015 - Digital Group - Edges

Meeting Notes March 2009 to 2018.
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spb
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Joined: Tue Mar 25, 2008 7:04 pm

April 2015 - Digital Group - Edges

Post by spb » Fri Apr 03, 2015 9:15 pm

EPSON PRINTERS
I have used Epson printers for 20 years and always recommended them for image quality, whilst readily admitting that they are often expensive and frustrating to own, with nozzle blockages, wasteful black ink swapping, software bugs and faults.

In recent months I have encountered more and more members who are so frustrated with their Epson printers that they are ditching them for the competition, usually Canon, or online printing services. The lack of any cost-effective and local repair facility and the continual battle with blocked nozzles are usually cited as the reasons. This is despite the owners knowing how to look after their printers and using them regularly as is necessary with inkjets. My Epson R3000 has been very prone to serious blockage problems after swapping the blacks (what is that two-blacks business all about?)

An unscientific show of hands at our meeting of 45 members revealed that a large majority owned Epsons and most were still happy with them. However a handful were contemplating a move. About five currently own Canons and all were happy with them. Watch this space.

IMAGE EDGES
Once we start manipulating images we have to control the edges that we create within the image – both their location and quality.

Sharp Edges – tests with a 24mpx Nikon, a 20mpx Sony and an 8mpx iPhone gave an interesting result. The hard edges from all cameras were approximately 4px wide. Clive Bartram suggested that this might be because of the way that data is collected from camera sensors using the Bayer array. Whatever the reason, the practical effect of this is that the edge of an image element should be no less than 4px wide to look realistic. Such image elements are usually created from selections and it might be reasoned that these should therefore be feathered to 4px. In fact this produces an edge that is about 16px wide! A feather setting of 1px is the most appropriate as it produces an actual edge of about 4px width.

In a given image, camera shake, inaccurate focussing, less than optimal aperture and lens aberrations may produce wider edges, in which case we should try to match those with our selection edges.

Note that anti-aliasing is an option with several tools. This only produces a one or two pixel softening and can be safely left on, and ignored.

I would recommend always working on the full-size image. If a lower resolution image is required eg for projection, this can be generated from a copy of the final image. Sharpening and any border should also be done at the final resolution.

Brushes – are the basis of many tools; Brush for painting layer masks, Healing Brush, Clone Stamp, Eraser, Blur, Sharpen, Smudge, Sponge, Dodge and Burn Tools. A hardness slider (sometimes difficult to find) determines the amount of feathering of the brush edge. The feathering is a proportion of the brush size so if we want a 4px hard edge, as above, some trial and error is necessary. It is apparent that 100% soft brush is soft over it’s entire width and is inappropriate for creating hard image edges. If there is no hardness slider for a particular tool, Shift [ and Shift ] are the keyboard shortcuts. Four of these take you from 0 to 100% hard in 25% increments. Square brackets alone control the brush size.

Quick Selection Tool – is an excellent brush-based tool in recent versions of Photoshop for generating a semi-automatic selection of an image area. This cannot be controlled for edge hardness and generally produces a hard image edge of a few pixels width – even when selecting a naturally soft-edged area. The Auto-Enhance option results in the tool producing a totally hard edge when selecting a totally hard-edged area but cannot produce softer edges.

Totally Hard Edges – ie no intermediate pixels. These are not photographic but are appropriate for image boundaries, borders and graphic elements only.

Blended Edges – when used to blend image edges eg from a too-soft Clone Stamp Tool, can produce a confused border area where both images are visible. However they are very useful when applying soft-edged adjustments eg with an adjustment layer and layer mask. Taking the example of darkening a cloud; the Lasso Tool can be used to draw roughly around the cloud and then the levels adjustment layer applied. The problem is that the amount of feathering of the selection must be chosen before the effect can be seen. A better method may be to apply Gaussian Blur to a hard-edged layer mask, in which case the effect can be seen and adjusted to suit.

Gradients – can be very useful when applying an extremely soft transition between two images or to an effect. By creating a linear black-to-white gradient in a layer mask a very gradual and controllable transition is achieved. Each mouse-drag creates a new gradient in any chosen direction. By reversing the direction of the mouse-drag the opposite blend is achieved. Note that a gradient can be added to an existing mask by choosing a black(or white)-to-transparent linear gradient.

Difficult Edges – whilst tools such as the Quick Selection Tool will help you to find the edge of an image area, none of the selection tools alone will achieve an acceptable selection of a difficult edge such as wispy hair, or feathers. For this, help is needed from the Refine Edge brush (CS5-on or Elements 11-on) or third party tools such as Topaz Re-Mask. These were described in APS Digital Group Notes of December 2012.

Edge Rescue – may be necessary when edges go wrong;
- an edge that is too sharp or jagged can be softened with the Blur Tool.
- an edge with a fringe of background colour can be fixed by selecting the layer, contracting the selection by a few pixels, feathering it, inverting it and deleting the fringe.
- chromatic aberrations are usually of a very distinct and abnormal colour(s). They can be removed with the Hue/Saturation palette (select anything other than Master, pick the aberration colour with the Eyedropper and desaturate).

Cheers, Steve Brabner

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