A look versus an effect

Ask one question of any filter and it falls cleanly on one side or the other. Does it change what colour things are, or does it change what the picture is made of?

The question

Point at one pixel in a photograph. Apply the filter. Now look at the same place. If what you find there is the same piece of the world in a different colour, you have a look. If what you find there is a dot, a square, a character, a smear of the neighbouring pixels, or a fragment that used to be somewhere else, you have an effect.

That is the whole test, and it holds up better than any list of names because it describes what the operation does rather than what it is called. Sepia is a look. Cross-processing is a look. Teal shadows and orange skin is a look. Turning a photograph into a grid of coloured circles is an effect, and so is reducing it to sixteen colours with a noise pattern hiding the steps, and so is scattering the rows sideways to make it appear broken.

The reason this matters practically rather than philosophically is that the two kinds want completely different machinery underneath them, and a tool that tries to do both ends up doing neither well.

Why a look is a table

A colour transform has a convenient property: the answer depends only on the colour going in, never on where that colour was or what was next to it. Two pixels of identical colour, one in the sky and one in a puddle, come out identical. That means the whole transform can be worked out in advance for a modest number of sample colours and stored — thirty-three steps of red by thirty-three of green by thirty-three of blue, so around thirty-six thousand entries — and then every pixel in a forty-megapixel photograph is a lookup into that table with a blend between the eight nearest entries.

That is what makes a rail of eighteen versions of your photograph affordable here at all, and it is what a strength slider leans on when it asks for the picture again on every move. It is one very cheap operation repeated, and a graphics chip does exactly that kind of work in hardware. It is also why a look is completely reversible in principle and why it never costs you any sharpness: the pixel grid is never touched.

Why an effect is not

An effect breaks that property immediately. Ask for a pattern of dots whose size follows the brightness underneath and the answer at a given pixel now depends on where that pixel sits relative to the pattern’s grid — two identical colours a few pixels apart come out differently, one at the centre of a dot and one in the gap between two. Ask for an ordered noise pattern and the answer depends on the pixel’s coordinates. Ask for anything smeared, scattered or rebuilt and the answer depends on the neighbours.

None of that can be precomputed into a colour table, because a colour table has no way to express “it depends where you are”. Effects need a different engine: one that knows the geometry, holds the whole frame, and often runs at a fixed cell size rather than at the photograph’s resolution. They also behave completely differently when you resize the result afterwards, which is a practical headache a grade never gives you.

So the two live in separate places on purpose. This site does colour: twenty-four named looks, film emulations, one strength control, and a promise that your photograph comes out with exactly the structure it went in with. The structural kind — patterns, dots, steps, characters, deliberate breakage — is the subject of a different tool entirely, and if that is what you came for then filterpicture.com is where it is done properly rather than as an afterthought here.

Edge cases the test still handles

Grain

Grain is the awkward one, and it is honestly an effect wearing a look’s clothes: it adds per-pixel variation that was not in the picture, so it fails the test. It is included in some grading tools anyway because a film emulation without it is only doing half the impression. Where it appears it should be capped low enough that it stays invisible at the sizes photographs are actually looked at, and it should never be sold as detail — it is texture laid on top, and it can only ever hide fine detail rather than reveal any.

Vignette

A vignette darkens the corners, which means the answer depends on position, which means it fails the test too. It is conventionally grouped with looks because it does its work purely by changing brightness and because it is what a lens does anyway. Call it a borderline case and be aware that it is one.

Black and white

Passes cleanly. Every pixel is replaced by a grey worked out from the three channels at that pixel and nothing else, which is a colour transform by any definition — and a much more interesting one than it looks, since the weights you choose decide what the photograph turns out to be about.

Using the test when you are being sold something

Filter menus tend to mix the two kinds without saying so, and the names are no help — plenty of presets called “vintage” are grades and plenty are overlays. Two quick checks tell you which you are looking at without any documentation.

First, zoom in. A grade looks the same at 100 per cent as it did in the thumbnail; an effect reveals its machinery, because whatever cell size or pattern it works at becomes visible. Second, watch the file size after saving. A grade usually produces a file within a few per cent of the original at the same quality setting, because the picture still has the same kind of content in it. Anything that has been rebuilt out of hard-edged repeating shapes compresses very differently, sometimes dramatically smaller and sometimes much larger.

What this distinction costs you here

Because everything on this site is a colour table, nothing here can give you a filter whose whole point is visible structure. That is not a feature waiting to be added; a lookup table cannot express it, and bolting on a second engine to do so would make the strength slider mean two different things depending on which look you had selected.
And because a colour table is all any of these looks is, none of them can act differently on the sky than on the face beneath it. A grade applies one decision to every pixel of a given colour wherever it sits. Anything that needs to treat one part of a photograph differently from another is selective work, which is a different craft with different tools.