Saturday, July 28, 2012

Basic Terminology, Part 2

Reference JPEG, Straight Out of Camera

Yesterday, I introduced the most common Picture Parameters, all of which can be preset within your camera to achieve desired effects, or manipulated by simple JPEG (or RAW) software after the picture is downloaded to a computer. Today, I'm going to get into more advanced Parameters, which usually need to be done with RAW files, unless noted otherwise.

Texture Contrast

Some RAW Developer Software has a Parameter called "Texture Contrast". It is a kind of "selective contrast". As it's name suggests, it adds specific attention to the texture details within a picture, which leads into a specific branch called "Texture Photography". In this picture, the most notable texture is that of the clouds, so here is the picture with a high amount of Texture Contrast applied:

Texture Contrast Added with Photivo

Local Contrast

Local Contrast is another kind of "selective contrast" that gives you control over specific tones within the picture you want to add contrast to, Because it is done at a Pixel level, it is sometimes referred to as "Micro Contrast". You can select whether you want to add contrast to the shadows, the mid-tones or the highlights, and also add variables in terms of soft or hard, and the "radius" (which always means the number of pixels you want to spread the effect out from - in other words, do you want to apply local contrast with a single-haired brush or a putty knife, or anything in between). Here, I've applied an extreme amount of Local Contrast to the mid-tones with a 100 Pixel Radius:

Local Contrast Added with Photivo

As most of this picture is composed of mid-tones, the effect can be seen throughout the entire scene, and is of course way too heavy handed, but this is all for demo purposes, right?

Colour Curve

This one is particularly useful, easy to use, found readily in all Photo Imaging software (even the one that came with your camera, most likely) and even works well on JPEG files. Is you picture too dark or too bright? Simply change the colour curve. It adjusts all three colours (RGB) equally. It allows you to brighten or darken a picture somewhat (not to great extremes) without losing any shadow or highlight detail. This should actually be the very first thing you should try on any photo downloaded to your computer - even if you think it looks OK, try it anyway. You can see here how the overall brightness was elevated, brightening the foreground, without loosing any of the nice detail in the clouds. 

Colour Curve Raised

Dynamic Range Adjustment

This is sometimes referred to as Compression, because the idea is to "increase" the dynamic range by compressing the RAW file into a decreased 8-Bit tonality. I find this quite hard to understand, and even harder to explain, because I don't quite get how you can increase something by compressing it, unless you perhaps look at it like "compressed air", where the air is provided with a lot of stored-up power when you compress it into a tank, or a car tire. Anyway, the effect can be quite dramatic, and it can only be accomplished with a RAW file, because only RAW files contain enough data to compress. So here, I applied a moderate amount of Dynamic Range Compression to the already elevated Colour Curve example:

Dynamic Range Compressed with Photivo

Notice especially how a lot of detail was picked up in the sky that was otherwise invisible. Don't ask me how! Obviously, the data for this detail was present within the RAW file, and made visible by dynamic range compression. This is approaching a High Dynamic Range (HDR) type of picture.

I've run out of time for today - there are still many other parameters to be discussed, but that'll be for another day.

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