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Spyder On... Filters (again)
The subject of filters, both physical and virtual is a big one. Like lighting itself it is a subject worthy of an entire book let alone a long winded article from yours truly.
I tagged a bit about filters in to the end of my intro on lighting, and I think that may have been a mistake. Ignorance is bliss and knowledge is power but if you deny ignorance but give too little information to empower, then you do a disservice.
So I will try to set that to rights with a full article on the subject.
Believe it or not, I do do some research when I write these articles. Part of the reason I write them in fact is to push myself into examining the aspects of photography that I write about. Upon returning to the subject of filters I have discovered one thing…
I’m getting old.
I know that because I have spent my time trying to show how real glass and tint filters are better than virtual ones applied in post production.
I cling on to old ways blindly… ergo, I’m getting old.
So let’s look at filters, both physical and virtual, hopefully without bias (ish).
A quick note before we get into the body of the matter, for this article I will be using Cokin glass filters and Photoshop, so I will refer to the filters used by Cokin codes and their simulation via Photoshop’s filters and image functions.
There’s a lot about filters I will not be repeating from last time to save space, check lighting part 5 for the details.
Now here’s a bit I missed out of lighting part 5.
Sympathetic colours
When I posted this people asked me, what’s going on? How come the picture colours look so stunning?
Simple, it’s sympathetic colours. The Magenta filter cuts out green, take a look on the colour wheel:
And you see magenta is opposite green, at 90 degrees to these colours are blue and yellow, the sympathetic colours. Sympathetic colours will be dulled by a filter, but with a bit of brightness/contrast tweaking they’ll be back in all their glory (sometimes autolevels works really well on this, other times not).
The bad news for all you digital filter users is that this process doesn’t work purely digitally, the ‘3 colour’ modes (RGB and CMYK, more on them later) don’t line up with this 4 pronged colour manipulation (the filter colour, the blocked out colour and the 2 sympathetic colours).
Types of Filters
Colour filters
A very quick recap, colour filters (effectively) add colour to colour photographs and remove it from black and white.
Solid colour
A blanket effect to the whole photo. With most colour photography subtle colour filters are the useful ones, generally anything more than the weakest tint will require editing, hue and saturation manipulation afterward.
There are exceptions
When it comes to colour photography ‘colour compensation’ filters are most useful.
Back in the bad old days of film, if you’d only got daylight film with you and wanted to snap away under florescent lighting or the horrors of the domestic light-bulb the only thing you could do to save the day was stick on a compensating filter.
These days digital allows us to compensate without panic, although it’s far from perfect. Compensation filters do win out over digital is this situation, under strong fluorescent light for instance, you can set your camera to fluorescent but this tends to ‘damp down’ the colour, which can blow the point of the whole photo, or you can drop the green saturation in Photoshop (channel mixer, select green channel) but this can be a difficult one to judge and can course loss of detail.
The best answer I’ve found is a filter (Cokin ref. 036 for strong, 046 for weak compensation).
As with all colour filters you’ll find a stop-drop using them, about 1/3 to ½ with the 046 filter and a full stop for 036 filter (spyder on lighting Prt 3 for details on F stops).
In this case you’ll keep the detail, sharpness and get a picture with a good strong colour saturation and no tinny greens or tinted reds.
Other colour filters of note well worth the effort over digital are:
Neutral Density.
These damp down highlights, reducing the stop range of a picture to bring it within your cameras capabilities.
Sepia.
Great for landscape/nature shots when colours would look washed out and flat.
Warm-up.
Actually a sort of orange. The effect (on white/pink/blue skin) is to give a tanned look as well as a perceived softening of the picture (this is a trick of the eye, there is no actual softening). This one can be done by Photoshop, but it can be a fiddly one to get right.
Replicating solid colour filters
2 methods to get this done, one is very straight forward and will probably be well know to all those who have a good knowledge of Photoshop, the other is a little more technical but faster to produce.
1. Filter layer.
Add a new layer to your picture, choose a colour, use fill on the layer then drop the opacity of that layer. An opacity between 1 and 10 percent will give you the effective filter range. Use Photoshop’s help if you need to know how to do this.
2. Colour channels.
I’ve briefly mentioned this before when dealing with colour temp.
Let’s go into it with a bit more detail.
Photoshop will allow you to choose a number of colour modes via the image->mode menu, we’re interested in 2 of them. RGB and CMYK.
Quickie note: If you use CMYK and I know a few who always do, don’t forget to convert your images back to RGB before you attempt to have them printed otherwise either the image will not be printed correctly or will not be printable at all (as almost all print systems use RGB).
With your image in RGB mode Photoshop’s channel mixer will give you 3 channels to manipulate (Red, Green, Blue), in CMYK you’ll get 4 (Cyan, Magenta, Yellow and Black) but for filters you’ll still be focusing on the first 3.
In a perfect world the channel mixer would give you Red, Green, Blue and Yellow channels to mess with, without all this mode changing.
The trick to simulating filters is remembering that colour filters BLOCK OUT certain parts of the spectrum rather than actually adding anything (unlike colour temp. compensation, which does sometimes require an increase in the relevant channel).
So to replicate a red filter, stick with RGB, open the channel mixer, leave red at 100% and drop the Green and blue channels evenly below 100% (remember to swap to the right channel before dropping the level).
For a Yellow filter, change mode to CMYK and do the same procedure (dropping Magenta and Cyan, leaving Yellow and Black alone).
This is why it’s easier to use a warm up filter rather than do it digitally. To replicate an orange filter you need to drop Green and Blue by around half the required amount then swap to CMYK and drop Magenta and Cyan. Your problem here will come in swapping modes. RGB and CMYK don’t quite mesh together so when you swap between modes it can change the colours of your picture, ruining the effect you were going for in the first place.
Once you’ve dropped the levels you’ll probably be left with a photo that looks a bit washed out, you’ve replicated the colour effect but not the effect on exposure.
Replicating the exposure change is mostly down to taste on your part but is done by stepping up the saturation, contrast and brightness of the picture (between 3 and 5 percent usually does the job when simulating a standard filter).
Quickie note: Use of brightness in this situation is a bit heavy handed, it is often better to use Curves (it’s in the image menu, under adjust). Bending the curves line up a little in the middle will bring up the lighting levels of your photo while preventing the loss of depth in the shadows or the risk of burning out the highlights.
Turning a colour photo into digitally filtered black and white.
Turning a colour digital photo into black and white couldn’t be simpler, just go into the image->adjust menu and choose desaturate.
Quickie note: You’ll probably end up with quite a naff looking B&W, try going into the Curves tool again and this time move in the high and low points just a touch, this drops the low point of the shadows to absolute black and the highs to absolute white, the ‘classic’ look for B&W photos, you may need to bend that curves line up a touch too just to expand the range of the remaining greys.
To replicate a filtered B&W follow the steps for a colour filter, but exaggerate the strength of filter used, for a red filter reduce the blue and green by 30, 50, 70 or even 100 percent, then desaturate the image. What you’re left with will probably look dull if not nearly black, you have 2 options for bringing it back to life, either autolevels (but be warned this can lead to the image burning out in unwanted areas, use fade in the filter menu if this happens) or its ‘brightness and contrast’ plus a bit of curves tweaking. Here’s a quick example:
Full sized version here
From left to right.
Original taken in daylight conditions.
Un-altered Black and white.
Red filter.
Green filter.
Blue filter.
Gradients
There is a TV program called ‘Top Gear’ here in the UK (it’s about cars). If you’ve never seen it, download an episode from somewhere. Any episode.
Wait for them to test a car and you’ll see gradient filters used in all there glory, I counted 15 different gradient filters in one of the programs (which shows how anal I can get).
Gradiated filters can be used in many ways and to startling effect, but the most common use is to decrease or increase the ‘presence’ of the skyline. A grey or even black gradient will subdue a very bright sky, a blue will make a washed out sky pop, and if you’re looking to B&W effects a red filter will make the clouds shine while virtually blackening the sky itself.
I’ve got to admit I prefer real gradiated filters to virtual ones, simply because you can see the effect before you take the photo, I don’t like snapping away and then trying to stick in a filter afterward. But I’ll freely state it can save an otherwise lost picture.
Virtual Gradiated filters
With Photoshop gradient filters are a simple thing to create but hard to do well.
To create one simply make a new blank layer, choose your colour and use the gradient tool to draw your new filter, drop that layers opacity to somewhere between 1 and 15 percent and you’re done.
The gradient tool has lots of fiddly bits to you can play around with, and I suggest you do. A good knowledge of this tool will improve the quality of your digital gradiant filters no end.
Startling colours
Just a quick suggestion, I’ve seen a lot of stunning photos using some startlingly coloured gradient filters, like bright orange over a skyline or purple across a forest view. Give it a try.
Optical effect filters
Generally speaking, optical effect filters are redundant these days.
There are star filters what will make lights flare in various ways, centre spots which blur everything outside the centre area, speed blurs that give images a ‘whooshed’ look, multi-image filters that make photos look like they were taken for an early 80s music video, mirror filters that reflect half the photo over the other half.
There are many variations on these themes and all but one can be replicated through Photoshop in seconds if the mood takes you.
The one you can’t? The close-up filter. Basically a socking big single element lens to slap on the front of your main lens. Cokin does 3 of these, called +1, +2 and +3 (bet it took ages thinking up those names).
A few notes of worth about the close up filter.
They turn any lens (that will fit the filter) into a macro lens. The focal range and depth will be massively reduced as with all true macro photography, the higher the value of the filter you are using, the greater the magnification but also the greater the effect on focal range and depth.
You can of course replicate this digitally, it’s called cropping, but with a close-up filter you don’t lose any detail or pixels in the process.
And that is quite enough.
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