Index (this will be updated as the series unfolds)
Part 1a: Importing Files and File Types
Part 1b: Camera Raw
Part 2: Colour:
Part 3a: The Workspace
Part 3b: Example Layers Workflow
Part 3c: Adjustment Layers
Adjustment Layers
Destructive Processes
Levels
Curves
Colour Balance
Brightness/Contrast
Auto Levels / Colour / Contrasts
Selective Colour (adjustment)
Part 4: Grouping, Masks & History
Part 5: Selection and Paths (Pen Tool)
Part 5b: Healing Brush, Patch or Clone Stamp Tool?
Adjustment Layers (intro)
Adjustment layers 'float' over image layers, where they apply particular effects to the layers below them in the hierarchy. Very much like layers, adjustment layers have adjustable opacity.
Destructive processes
The main difference with adjustment layers is that they perform 'destructive processes' (for the purposes of output) - that the adjustment will, to a certain degree, diminish the quality of the output image. This could be so minor that the human eye would not be able to tell, but if more extreme adjustments are applied then there will be irreversible diminishing of quality for output. This is manifested in the form of banding, excessive dithering and limiting of colour (and is the reason why the original image should always be duplicated in advance of editing).
Technical note: A 'destructive process' is described as a process that diminishes the source image. Given that adjustment layers can be toggled on or off separately to the source image itself, they are technically non-destructive to the file and only destructive to the output image.
When you take a photograph, it is an exposure; a balance between light and dark. It is quite possible for the highlights to 'blow out' or the shadows to go 'blocked out' - over/underexposed to the point that they technically don't contain information, so are rendered as black or white. Excessive image processing can cause a similar issue where levels are pushed well beyond their original means - what is not captured within an original image cannot be created from nothing.
The same is apparent when referring to image colour. It is possible to over-process and push colours too hard or utilise areas of the working colour space that are outside of available outputs formats (i.e. it may be for screen, but wont be possible for print).
Levels
Create new fill or adjustment layer > Levels
Levels are there to correct the tonal range of an image - the black of the blacks, the white of the whites, and your midpoint tone. The histogram is a visual representation of your image that helps in presenting where information within the image is against in tonal scale. The three anchor points (also represented by the three eyedropper tools within the levels menu) can be adjusted individually to change the low (black), mid (gray) and high (white) tonal values.
Best thing to do with levels is to play - slide the pointers in excess to see what they do to your image, then you'll quickly figure it's best to only use subtle tweaks for fear of turning your family snaps into alien portraits.
The eyedropper tools are a quick way to reference a specific area in your image as being the black, grey or white point. Click the appropriate of the three and click it on your image - the reading will then be interpreted as your new level. Be warned, however, if you click around your image with the accuracy of Gareth Southgate, chances are you'll end up with your whites turning blue, your midpoint pink/black and all manner of visual mishaps. If you take a spare picture at the same time with a grey card in the shot, the eyedropper tool suddenly becomes stunningly accurate; simply save these settings and then apply them to the proper image.
Curves
Create new fill or adjustment layer > Curves
Curves are like a more accurate version of Levels - main difference is that you can adjust by channel (Red, Green, Blue or all / Cyan, Magenta, Yellow, Black or all) for colour level correction.
The interface shows the tonal range as a diagonal line - highlights top right, midtones centre and shadows bottom left. This line can be clicked to generate a new anchor point, then pushed and pulled into a new curve that will adjust the levels as visually plotted on the graph. It's possible to plot multiple anchor points, where the curve will follow this arrangement - this can be useful for trying to, for example, hold top end highlights, whilst dipping the midtones into a lower tonal region.
Colour Balance
Create new fill or adjustment layer > Colour Balance
Anyone familiar with traditional darkroom colour printing will instantly see the equivalent that this feature offers.
Think about the classic colour wheel and you may remember that colours work in polar opposites - i.e. Cyan/Red, Magenta/Green, Yellow/Blue are opposites within a colour space. Adding more of one will take away more of the other and vice versa - so an overly red balanced image needs to become more cyan to counter and become an accurate balance.
The major difference to being in the darkroom of course is that you're making adjustments on a screen in seconds, compared to the hours it can take to traditionally print.
Oh, not to forget that (much like Levels and Curves) you have the manual colour control of shadows, midtones and highlights - but it's just colour changing hands here, not the tonal range.
Brightness/Contrast
Create new fill or adjustment layer > Brightness/Contrast
One to be used with caution, pushing the contrast of an image can only be achieved by axing other available data. On screen contrast also differs significantly from print contrast ratios - given that one is directed light, the other reflective. So “punchy” on screen might mean “crap” on paper.
Auto Levels / Colour / Contrast
There are automated processes of all the above - but be warned, they are based on mathematical processes, so you may find your pink image turns cyan with blown highlights, for example. In the right circumstances they are extremely useful:
Image > Adjustments > Auto Levels (Shift+Ctrl+L)
Image > Adjustments > Auto Contrast (Alt+Shift+Ctrl+L)
Image > Adjustments > Auto Colour (Shift+Ctrl+B)
There's no “Auto Curves”, but Curves are essentially a subtle way of adjusting Levels via a graph-based interface.
It can be worth testing the processes out and 'undoing' (Ctrl+Z) if dissatisfied with results. Working by hand is far more rewarding if well practiced, but much more time consuming.
Selective Colour
Amid the tools for black and white conversion, exposure, hue/saturation and all manner of others, Selective Colour is the one distinctive addition to the colour correction palette. This allows for image colour editing that is only possible by digital means.
Colours can be selected and then the balance for that specific colour can be corrected. It's a subtle tool, but can be really effective for certain results. The before and after images below show a boost of yellow and dip of magenta has been applied to any red in the image. Not the red channel in RGB, as this would affect the other colours in relation to the adjustment - but the colour red within the image has been individually selected for adjustment. Notice how this has taken the pink out of the cheeks, but there has been no traditional colour change to the greens in the eyes and the blues in the background.
Continue to Part 4 & Grouping Layers, Masks & History...
