Matching Elements Workflow
Compositing is the act of visually uniting one image (foreground) with another (background) in such a way as the 'join' between the two is invisible. This requires a separate consideration of the following values:
Color is a small word for a large thing. Color is composed of lightness, saturation and hue values.
When matching the foreground with the background it is sometimes wise to switch off their color values so that they do not distract. This can be done by placing a Hue Saturation Adjustment Layer above them with the saturation value set to zero.
- The highest and lowest values should first be matched. If the two are both normalized then this is likely to be unnecessary as both the black and the white have been set.
- The middle values of the foreground can be changed using a gamma or contrast operation.
- A clipped Multiply clipped layer blend can be used to paint in any local darkness that is required. Be warned: you will need to have good painting skills in order to make this work.
- Likewise a Color Dodge or Screen clipped layer blend can be used to work upon the lights.
- General tonal 'noise' can be added with an Overlay clipped layer blend and a texture that matches that of the background. This should be de-saturated first to ensure that no hue values are passed on.
For an introduction to what saturation is have a look at the Hue Saturation page.
- For a general saturation adjustment the Hue Saturation Adjustment is the tool of choice.
- Local saturation values can be made with a Saturation clipped layer blend. This will pass on the saturation values of its content onto anything beneath.
- An interesting and sometimes useful saturation contrast technique outlined in the Selective Color Adjustment page.
What is hue? If saturation is the 'amount' of hue then hue is the 'name' of the color: the red, blue, green, yellow etc of it. Hue matching is a complex proposition. This is because hue 'lives' in three values (RGB) not one (amount) like lightness and saturation.
- Saturation and lightness can both be dealt with by using good judgment and a sound pair of eyes. When tackling any hue issue it is often helpful to do it through the numbers via the Info pallet. The job is to identify in the foreground and the background two areas that should match and the write down the RGB values of both. The task in hand is now to get these two values to match. The best source / target pair is of a low-mid light value (hue is most apparent in this range).
- No matter how attractive it might look, avoid the Color Balance Adjustment when editing hue values. It is a crude tool that has a better reputation than it deserves.
- The best hue editing tool is (of course) Curves. Normally, the best way to use it is with a gamma adjustment to its middle values. Why? Think about it... is there any hue in a black or a white? Of course not. Any curve adjustment that encompasses these values is in danger of damaging these color-neutral points.
- On the other hand... sometimes the lightest points do have a color cast in them. I leave it to you to discover the exceptions to any rule.
- A Hue clipped layer blend will change the hue value of the foreground. It will not affect the grays or the whites. This can be really useful if you are dealing with something essentially monolithic in hue value like a face. Simply select a large portion of the source and cut and paste it into a new layer. Then pass a Gaussian Blur or an Average filter onto it. Clip it above the foreground and set it to Hue clipped layer blend. This will magically conform the hue values of the foreground with those of the background.
- A Color clipped layer blend will also change the hue values of the foreground, but will impart a hue value on the neutrals.
It is an irony that we often need to dumb down the information that we feed into our composites. It might be that our forground image is of a way better quality than our background.
- A Grain filter is, unsurprisingly, the tool of choice for adding photographic grain. I find that the Clumpy preset to be the best for this purpose.
- If you want to do it non-destructively then pass it onto a layer filled with solid mid grey and set it to an Overlay layer blend. This can then be edited with curves to soften the grain.
- Though Grain is the best tool for this job that PS offers, it still sux. A real grain varies greatly in intensity from channel to channel. If you are super picky about it you can run the filter on the different channels to different degrees (using the background as reference).
- If a large enough sample of the background photo is available, then you may cut and paste a plain, even section of it onto a new layer, and set that to Overlay. You may have to color match before you do.
- Again, if you are super picky then you might take a photo of a grey neutral with the same camera as was used to take the background photo. This can then be used in Overlay mode.
- De-grain? Good luck. Maybe you can try a Reduce Noise or a Median filter.
Blur with a Gaussian, Box or Lens Blur. Remember, you may need to do this along the depth plane.
De blur? ha!
If there is one thing in compositing that is commonly done wrong it is edges: they are frequently too sharp in the foreground mask or, if the, mask has been carelessly done, too vague.
- Edges can be masked by blurring then slightly with the Blur Tool.
- If the original background to the foreground was much lighter than the new background then there is likely to be fringe artefacts to deal with (see the paired images below). The way this is dealt with is the mask can be Command Clicked to get its selection value and the resulting selection stroked with a black line. This is blurred and set to multiply. This is likely to require some touching up if it is to look ok.
If I have given you the impression that all you need to do in element matching is to follow all the procedures laid out above then I apologize. In real life no two cases are the same and exceptions are often the rule. Take the situation below: the original sky was a lot lighter than the background onto which it is to be placed. A good deal of hard-core creativity will need to be employed if the two are to meet.
The solution employed the following solutions:
- To the background
- A Color Dodge layer blend to increase the luminance of the lower sky.
- A multiply to darken the top sky.
- A masked Curves Adjustment Layer to darken the upper sky.
- To the foreground
- A paint layer to soften the cast shadow of the tree (evening light produces softer shadows).
- A Hue Saturation Adjustment Layer to de-saturate slightly the foreground.
- A blurred background set to Hue blend mode and made slightly transparent. This will cool slightly the hues of the foreground.
- A stroked outline (derived from the foreground layer mask) blurred and set to Multiply blend mode. This darkens the edge. Some erasing and painting was needed to draw in the shadows and light areas (note that the tree gets lighter towards the top).
- A Curves Adjustment Layer to darken the foreground.
- To darken and make less sharp the shadows a copy of the tree was desaturated, posterised and blurred a little and the result was set to Multiply blend mode. This was then masked with complete black and selectively painted back in.
Though, as a general rule, we treat either the foreground or the background as the target of a match, it is often the case that we end up adjustment both. You will notice that the result looks a little 'painted'. This is almost inevitable as the foreground and background were so different.
The demo file for this page is available in the Assets page.