Digital image retouching and processing

Frequently, the images which we have have some not-so-good parts (or they are directly unacceptable) and is necessary to alter them. For a conventional photography, this means a painstaking dedication and great experience; with digital media you can retouch, process and edit in many ways, easily and quickly. Combining, changing, eliminating or adding parts of an image, or several images is a piece of cake, compared to what the previous photography system involved.

Painting and photographic retouching software such as Photoshop include always a collection of filters for the modification of images. All of these filters are based on one simple method: individually or group changes of the the mosaic of pixels that builds up the digital image, the bitmap. This is how it takes place any change of colour, tonality, brightness. All the conventional classic photographic laboratory and processing techniques are still available, along with many other new and unsuspected ones.

Shall we convert the image to a cubist painting...?

...Distort it as a grotesque picture...?

...Wavy effects...?

...Crystalisation...?

...Colour halftones... and stepping a little we see the normal image...?

...Painting effects...?

Filters ans masks.

Any change in the bitmap image can be achieved altering the basic parameters of the image: contrast, brightness, colour balance... these changes take place on a pixel by pixel basis. Naturally, they are applied to the whole image, or to whole groups of pixels, if we have made a selection of those pixels with one of the different selection tools from the program: the magic wand, the lasso, rectangle or elliptical frame, the pen...

If we want to apply the changes only to a selection within the image, we must use a mask or reserve —an area that is affected by the changes, whereas the rest of the image is protected of any change until deselecting that area, as we show in one example in the bitmaps article. The filters are adjustments of the way in which the image changes (the whole image or partly) until giving a certain final result. For example, you can turn the image into a series of big points, or you can distort it. These filters have many applications and they save lots of time, mainly because to obtain their results they can be tweaked with different parameters, something would be quite complicated if we tried to do it directly. Each program includes a special collection of these filters and effects; it is also possible to obtain complementary collections (plugins), some free and other commercial. For example, there is a huge supply of plug-ins for Photoshop, which lets you creates very peculiar and striking visual effects.

The actions (scripts or macros in some programs) in the photo-edition programs are something still more complex: they are a macro, this is, a series of concatenate operations that take place to change an image. For example, to get rid of the background and create a projected shadow. The actions perform a series of partial changes in the image, more or less laborious, which can be saved recording every step as an action, a special kind of file which can be replayed later to get the same results. A very useful example: preparing an action that automatically creates a miniature in a specific size for the images in a folder, and then saves them in the chosen format and the subfolder that we indicate.

It is necessary to make a point about filter use and abuse. The filters do not have to be used indiscriminately. Some are amusing and striking, true: they really call the attention, but to abuse them is rather boring and tiresome, as it happens with so many things in life. Just as lame 3D effects, right? The images must be used for some purpose, according to which they symbolize, they mean or they suggest. Pictures often need only minimal changes and absolutely no special effects: they often look like some sort of cheap trick. Even so, the available arsenal of effects is great and everybody feels like exploring it. Some programs like PhotoImpact, remarkably simple to use, show a simulation of the effect that you will obtain with each filter and they display it as a gallery of images, so that it is easier to get the idea if the filter will do for your intentions or not.

Cambiar el modo de color de la imagen.

All programs let you change from a given colour mode to another (for example, to change from a bitmap in black and white to 24 bit-colour.) Some conversions are, indeed, necessary: in order to save as a GIF or a PNG-8 the number of colours must be decreased to 256 at the most.

To change an image to a format more restricted in the number of colours has a series of associated problems. In the first place, it must be decided what will happen with the colours that will “dissappear”; how are they going to be simulated in screen? You can either use a pixel diffussion or an ordered pattern, or even a halftone, with points made with the colours still available in the reduced palette, or simply assign a substituting colour. The first system (diffussion) can give acceptable results, but the size of the files tends to increase, since the image loses simplicity, with the greater number of points to define.

When we want to carry out an opposed change, for example, to convert an image in colour to black and white, sometimes the results aren’t as good as one could expect. A highly contrasted image is usually easier to transform (and, of course, a black and white drawing scanned as grayscale or colour is also better converted to black and white bitmap, as we discuss elsewhere.) In order to carry out the conversion we have different options: to change to the colors according to its proximity to the black or white, establishing a threshold, or to simulate the intermediate tones with patterns of black and white points, regular or irregular (diffusion.) Experiencing a little with these options quite different results can be obtained. Finally, if we place one of these images which we have converted to black and white over a background in colour, we’ll get a new and interesting version of the image.

Tricks, compositions and collages.

The painting and photo-edition programs make this kind of work easy. We even have some specialized tools, like the clone brush (a brush that copies an area of the screen on other parts of the same image.) The transparency effects and feathering of selections are vital to obtain subtle and creative effects. Some graphical artists produce surprising realistic images in the magazines and other printed materials. With a little dedication you may create really eye-deceiving composite images.