Basic Tips on digital images

by Inkraz Store on March 02, 2021
Textile personalization professionals need to continually handle digital images. Therefore, it would be advisable to be clear about the concepts explained below, they are already the basic foundations to understand how the images are saved and also to know if their quality is sufficient to print them at the desired size.

The first thing to know is that there are two well differentiated image formats: vector and bitmap. Later we will see how to evaluate the quality of a bitmap.

Vector Format
vector1 Images are saved as geometric shapes: lines and curves of any kind, but also texts. They are generated in graphic design programs such as Corel or Illustrator, they can never be photos. Its extensions are those of these programs: .cdr (Corel), .ai (Illustrator), .cmx, ... although there are also free, non-native formats (that is, not associated with any program) such as .svg.

Their most interesting feature is that they do not lose quality whatever the size to which we scale (enlarge), they always look good. Another feature is that they usually take up little space (if we compare them with bitmap).

Bitmap or Raster format
Bitmap VS Vector 04 Bitmap images are made up of points, which are called pixels. The images we obtain with a digital camera are of this type. Image size is measured in the number of vertical pixels by horizontal pixels. But the quality with which we see an image depends on the pixels per centimeter at which it is shown to us on the screen or on paper. That is why an image with a few pixels cannot be enlarged very much without being “pixelated”. That is to say, contrary to what happens with vector images, we cannot enlarge them indefinitely without losing quality.

The most popular bitmap extensions are .jpg .gif .bmp .tif .psd .cpt .tga. Most are not native to a specific program. If we want high qualities, the files will necessarily be large. Some formats partly solve this by compressing their data (.jpg, .gif).

Acceptable quality
Once this is explained, we will explain what can be considered a reasonable quality for a bitmap image, especially for a more or less professional printing. Of the vector images it is not necessary to do this explanation, because they can be extended indefinitely without losing anything of yours.

Bitmap VS Vector 00 The commonly accepted ideal measurement for quality prints on paper is 300 dpi, which is 300 pixels in each inch (on a computer screen a quality between 72 and 96 dpi is sufficient, depending on the screen size). If we translate those 300ppp into our decimal system, it would equal about 120p / cm. To facilitate a quick mental calculation, we could round this figure to 100p / cm, but taking into account that in important works we would have to adjust the figures to the real value.

With this simple reference of 100p / cm it is very easy to know what maximum size we can print an image of, for example, 1200 × 800 pixels: 12 × 8 cm (10 × 7 cm if we adjust the calculation).

Therefore, it is easy to adjust the image quality of the quality to the size in which we will later want to print the photos. Or to know if the image that they have asked us to print on a t-shirt has sufficient quality for the size in which they want us to print it ...

Transform from one format to another
The next question that anyone can ask is whether it is possible to switch from one format to another to take advantage of the advantages that best suit them.

Going from Vectorial to Bitmap is easy. As the vector is scalable to the size we want, just choose the size and process the image with a program. After all, all graphics programs do this when they send an image to the printer, since printers can only print bitmaps.
The reverse process, from Bitmap to Vector is much more complicated. In some cases, if it is complex images, almost impossible. It is necessary to use a program that processes the Bitmap image identifying the points that form a line or a curve to draw it. That is why they are called Tracers. It takes a good program and some experience to get good results.
In principle, it is clear that the second process would be the most interesting, but unfortunately it is not suitable for beginners. It's a matter of practicing with vector formats first and gaining the necessary experience ...