Post Processing and Effects

From RetroWiki'd
Jump to navigation Jump to search

Key vocabulary to remember

  • Under and over exposure
  • Transparency and the alpha channel
  • Aspect ratio
  • Chroma keying
  • Layers and composition

Apple IBook G3 12.1"


Image editing involves a vast array of techniques aimed at making pictures better fit your expectations, use for artistic or illustration purposes, and much less frequently as a result of publishing medium requirements.

Post processing refers to extensive editing that severely alters the original image. It can involve adding a transparency layer to a standard picture and even be as extensive as removing certain objects and features shown in the original picture.

All image editing and processing activities start as experiments, meaning that multiple attempts may be needed and results depend on the original photos, creativity of the editor, platform where your image will end up. Only after hundreds or thousands of such experiments you may find what is suitable to you or your activity.

Adding transparency

No photography ever has transparency by itself, no matter how well it looks. The camera can only make a better or a worse initial picture that showcases a product in a particular background. Even lighting and various techniques may make it seem that the product is neatly placed in front of an invisible background, but it still has no transparency. True transparency is achieved as part of an extensive editing of the initial picture, taking quite an extensive amount of time to reach good results, particularly when the initial image is complex or has an unevenly lit subject.

In order to add transparency you need advanced editing software such as the freely available Gimp and Krita, or commercial one such as Adobe Photoshop. In the process of adding transparency you will split your initial image in two layers, one will be the background, empty, the other one will hold the actual picture you will edit. This is the easiest and most versatile approach to editing. As you remove parts of the upper layered picture, the background will be more noticeable, until it will fully take all the space outside your subject.

The process of removing image pixels outside the boundaries of your subject may seem logical, but no application can make the same guesses as you in terms of how to interpret the parts of the image that should be discarded. Using the typical "magic wand" tool to select the outer area to delete may work on highly continuous areas and in excellent light conditions, as the algorithm has little issues in deciding what seems as background. However, in more than 90% of original pictures, this is hardly the case, you have to use another method to carry on your task.

The most likely way of achieving a good transparency is simply to draw an outline that selects the area that should be discarded. This involves using tools such as the "lasso" to carefully select points that should be marked as the edge of your subject, and drawing this outline slowly, step by step, around the picture, with a zoomed-in picture and having an extremely steady hand. It is better to select smaller areas to later remove as this reduces the chance of an unsteady click ruining your 5 or ten minutes careful tracing of the edges. Instead of using a lasso you may draw a filled polygon, which has the additional advantage of being less likely to suffer from the risk of not undoing your last missed step. This polygon will be ended either very close to the last step of your tracing, or exactly at that final point.

I generally suggest you not closing the polygon on the first point you draw of that outline, as it would offer the chance of creating additional sides to id that extend from the outline until each edge of the picture. In this way, a very large area can be covered and deleted in one go, when the polygon is selected and removed. This would create a clear outline that is very easy to evaluate. If the outline is not to your liking, you can undo a single step and attempt to change some of the polygon side intersection points, altering easily your process. When the polygon and subsequent removal of the area painted over is carried out, you are left only with a small sticking part of the original picture that can be easily selected using a basic rectangular selection tool and subsequently removed.

The final result of the process is an original image layer that has a cutout, where all the image information that stands beyond this edge is marked specifically as having no content. This resulting image cannot be used as is, since the format used by the program is different than the one of your publishing medium. To achieve usable image files you need to export this picture into a format that holds transparency information, or the so-called alpha-channel. A common, modern format is PNG, that also offers slightly smaller files, without affecting image quality. Subsequent editing while maintaining the PNG format also has the additional advantage of portability beyond accuracy, as all the original information is well retained and possible to edit in just about any software. Exporting is quite well managed by most software information, being assumed that your image should contain all your original layers. In case this option is not well considered by default, you can specify it when asked by the program.

The final result of your work must be exported from the image editor in a format that can store transparency information, such as PNG, Targa and others. These file formats can store the properties of every individual pixel, including the transparency, hold in a special data format, commonly known as the Alpha channel. This is in contrast to typical image storage formats that have only the Red, Green, Blue, or RGB data stored. Keep in mind that editing file formats that have transparency requires compatible applications or web platforms to preserve this information. Most simple editors such as Microsoft Paint, will discard such infomation, leaving you with a file that no longer is able to make use of transparency. Most web platforms such as web sites content management systems, on-line shops, social media sites, can and do use transparency, if your file holds such information. Seeing what kind of information is stored and if your image has transparency can most reliably be determined in advanced image editing programs.

Adding transparency, in most situations, means editing a standard image and specifying how each pixel's transparency is specified. Note that only certain image formats may hold a so-called Alpha channel information, JPEG cannot do this while PNG can.

Chroma Keying

No post processing and effects section is ever complete without chroma-keying. Although the end results are similar to adding transparency, chroma keying offers not only automated or simplified manual content creation but, most importantly, caters to video and movie or film production. In its most basic form, chroma keying helps by using a background colour that is rarely present in your subject, such as an extremely bright green, and simplifying the process of creating an artificial transparency around the subject, by extracting only that colour tone and leaving everything else intact.

A successful chroma key depends on a lot of aspects, such as uniform lighting, the absence of the background colour on the subject, a good software processing that understands subtle intensity or saturation changes in the background and still treats the area as background, as well as good blending in the fringe area between the subject and the background. Despite looking deceivingly simple, success chroma keying requires a lot of processing. As a result of that, for photography purpose, chroma keying is only a post-processing effect.

A good chroma key depends on uniform lighting and a good choice of background colour. A successful chroma keying setting can massively improve the chances of creating very good transparency effects on subjects with minimal effort in the post-processing stage.

Layered compositions

It is difficult to have all your subjects in an ideal composition. For situations that require less realistic effects, compositing, or creating an image which includes different subjects that were never parts of the same scene is popular for many activities, particularly in advertising. To achieve such effects, you obviously need photographs that have similar intensities and colour appearance. The whole composition, is however, a result of imagination of the editor.

A layer may be comprised of a single subject, a multitude of them, the background, a set of graphical elements such as lines or other geometrical objects. There is no limit to what a layer may contain. As you will notice, objects with good transparency can be placed closer or farther from the viewer to achieve the desired effect. Layers are flexible also in the way in which their apparent dimensions are handled, improving abilities to distort the composition as required.

To achieve good results you have to result to using advanced image editors, free or commercial products, that allow layering. If you use GIMP, Krita or Adobe Photoshop, or any other popular image editing program, you are already having the prerequisites met. To develop successful compositions, you have to get accustomed to using layers. Think of layers as nothing more than images that can be placed in a back to front order, as required. Their size, transparency, placement, colour, dictates what options are available. Even if the final image exported as a JPEG or PNG or any other format may or may not have transparency itself, the end result is a single layer image. All editing and creative options are left in your image editor. It is advisable to experiment with work on layers to have adequate flexibility in handling any task and unleashing your creativity.

Most images that are eye-catching in advertising or visual communications use a result of compositing, or using multiple layers, placed in a carefully considered order and edited carefully, to create a a desired effect. It is highly useful to experiment with layering in image editors that support this feature.

Advanced effects

Complex effects may be applied to images and there is no limit to what an application can offer by itself or through the use of plugins. When applying such effects the best approach is to keep the original image and any intermediate one with various degrees or emphasis applied. For instance, when you colorize a picture or when you blur certain parts of it, I advise to save the same image with effects applied at various intensities. After you have these images, review which one looks best to you and also ask for opinions. Do not rush, as some results may seem more appropriate on the rush of the moment but they may not seem as such after you let a day pass.

Most of the time, effects are organized based on the perceived impact, whether they apply the initial photography on a 3D object or they use mostly 2D effects. Classic 3D effects are spherical and cube mapping, extrusions, although the list is much longer than that. Popular 2D effects include various types of blur, geometrical distortions, embossing, smaller or larger area pixel effects, colorization.

There is no right or wrong way to apply effects and results as well as critical acclaims are highly subjective. As a rule of thumb, it is better to be more subtle than overt, so effects applied in moderation are more likely to be appreciated.