With Image Processing its best to start with the major changes and work your way down to more detailed adjustments. Its all the more important to do the major changes first as these changes will quickly reveal flaws in the image, so that you can later concentrate on the other minor changes that need to be made.

The biggest changes in Image post-processing are related to changes in luminosity, which can be referred to as changes in ‘Brightness and Contrast’ of all the pixels that constitute an image. Brightness is the lightness or darkness of a group of colors and contrast is the degree of difference between light and dark colors.

In this post we will take a look at the Auto commands of image processing (Auto Contrast, Auto Levels and Auto Color) that are part of almost every Image Processing software available.

Original Image

scotland forest

Auto Contrast

scotland forest - auto contrast

‘Auto Contrast’ locates the darkest color in an image and makes it as dark as it can be without changing its color. It then makes the lightest color as light as possible. The color balance remains unchanged. We can see that in the above image light green changes to a darker green and yellow becomes a little more lighter and brighter.

Auto Levels

scotland forest - auto levels

‘Auto Levels’ makes no attempt to preserve colors. Instead, it analyzes each color channel independently and makes the darkest color in each channel black and the lightest color white. The result is more often than not a shift in color balance. In the example above the color cast shifts from a reddish to a bluish one.

Auto Color

scotland forest - auto color

‘Auto color’ like Auto Levels deepens shadows and lightens highlights on a channel-by-channel basis. But where Auto Levels may shift shadows and highlights from one color to another, Auto Color tries to change them to neutral grays. Auto color also evaluates the midtones in an image.

 

Each image deserves a different treatment as there is no set standard for post processing – what looks good to your eye is what works best! I would recommend to start with these Auto commands for Image enhancement as a first step and once familiar with the work process get your hands dirty with the manual process of Digital Image Processing!


Anoop Hullenahalli

An Electronics Engineer working on wireless embedded systems for a living. Traveling, photographing and sharing my experiences here at ANUBIMB helps me unwind and break the monotony of life.

2 Comments

Sarah · 17 Apr ’11 at 1:15 pm

Thank you for this informative post! love it! Sometimes I need to do post-processing for my food-pictures especially when the colour of the food is very light throughout. Now i have a better idea what to do 🙂

    Anoop · 17 Apr ’11 at 2:34 pm

    good to know that it was helpful!

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