Pixels, formats, focus, resolution, sizing... What's what? Do you work with communications and need to refresh your image processing memory? Then read on! In this article, we have enlisted the help of photographer and retoucher Maria Stranger to improve our imaging, including the technicalities for attaining the best quality. Give the article a read and save it or print it for future reference should your memory fail you!
About Maria Stranger
Growing up with a father who was a photographer and who held photo auctions, Maria was surrounded by cameras and photography. Maria continued on her father's path by training as a photographer and image processor. She started her career at the photography department of the Swedish National Heritage Board in Stockholm, where she stayed for 15 years. She then worked at Johnér bildbyrå for just over 10 years. In 2013, she took the leap into the world of freelance and continued to work with Johnér, but then as her customer. She lives in Södermalm, Stockholm with her husband and dog, and couldn't be happier with life.
Pixels, file sizes and bit depth
A digital image is made up of pixels (px), something like the grains in an analog film role. In the computer, each pixel's light value is represented as a code of zeros and ones. And these pixels are used for sizing an image.
The digital size of an image (file size) is measured in kilobytes (KB), megabytes (MB) and gigabytes (GB), in order of size.
The bit depth (also referred to as pixel depth or color depth) indicates how much color data there is in each of an image's pixels. The more data bits per pixel, the more available colors, the more exact the color replication and the larger the size.
Different format types
TIFF – used primarily by photographers and printers. Works on most platforms and has a non-destructive compression, LZW compression.
JPG – used on the internet and may be destructive if used in ongoing image processing and: saves – opens the image – processes the image – saves the image again. Over and over again.
PSD – is a Photoshop format in which images can be saved with layers, channels and selections for future
EPS – is basically the same as TIFF, but is ready for print.
PNG – used on the internet and is a non-destructive format suitable for non-photographic images with large areas of color, such as icons, drawings and graphics.
GIF – used for simple animations.
Focus is important in an image. The depth of field is the part of an image that is in focus. The entire image may be in focus, from the foreground to the background. A short depth of field entails that only a small part of the image is in focus, such as a portrait in which the subject's eye is in focus, but everything else is blurry. This tactic can be used to give extra weight to your message. The eye is automatically drawn to in-focus elements, so you can highlight what you want the viewer to pay attention to by making it the only element in focus. Then there is motion blur, when the subject of the image is moving and blurry to relay the message of motion and speed – a commonly used tactic in sports photography.
At times it may be necessary to crop an image to ensure that your message truly comes across, or to fit into a particular format. Perhaps you aim to remove distracting elements from the image or simply to create a new dynamic through cropping. You can also create certain effects by cropping out elements. Ensure that you have some margin when cropping and that elements you want in the image are not too close to the edges since these may be cropped in printing.
To crop an image, you an use the cropping tool directly on the image in Photoshop. This tool allows you to drag the black-marked corners or sides, which become visible so you can decide how to crop the image. By keeping the cursor a bit outside a corner, you can straighten the image if necessary. You can also specify the size and proportions in the menu. Another cropping method is to open a new Photoshop template in the desired format, drag your image into the template, and
adjust the image upward or downward, that is, cropping your image with the cursor from a corner. Play around to find the method that suits you best.
Size and resolution
Different end products, such as paper, internet, tablets and slideshows, make different requirements on conversions and adjustments of images. Your images must be adapted to resolutions, color work spaces, sharpening, etc to convey the best possible message and to be of the best quality.
It is wasteful to use a larger image than the end product requires. The image will not look better just because it has a higher resolution. Instead, it will only be larger and require more space. You are best off using just the right size for your purposes. However, avoid using a smaller size due to pixelation. The individual pixels will become visible and the image will look strange.
The size and resolution of your image is important. Technological development, such as improved imaging on computer screens, means that it is vital that your images are of good quality. When using an image online, only the height and width in pixels are important. Websites can have dynamic windows so that there can be more pixels in the image than the window size, resulting in better quality that suits the quality of the screen. This is good when zooming in so the image maintains its quality. Resolution is only important when an image is printed.
Generally, a resolution of about 300 ppi is used for printed images and about 72 ppi for online images. However, this can vary. For example, different prints may require different resolutions. Images must be adapted to varying rasters, raster densities, paper types, coated and uncoated paper, etc.
The motif also determines the size of the image
In addition to considering the size, you should also consider the motif's contents when selecting images for online use. Small, highly detailed images may give a muddled impression and may detract from the meaning of your motif. Simpler and clearer contents make it easier to understand the message you want to convey with your image. Every once in a while, pull back to get an overview by viewing the website or other product in its entirety while working with your image.
Highly detailed images require high resolution whereas less detailed images can often be printed in much lower resolution. Large images, such as facade advertisements, do not need to be printed in high resolution since the image will not be viewed close up.
Sizing means enlarging an image, an increase in the height and width of pixels. In Photoshop, this can be done via: Image – Image Size, size the image and select the following settings: Automatic, Bicubic (smooth gradients) or Nearest Neighbor (hard edges) and so on, to size your image and give it the best possible technical quality. Different motifs may require different sizing settings.
Nowadays, sizing is good in Photoshop, but always review your image carefully afterwards to ensure the quality. However, it is optimal to start with the largest size necessary for your end product without having to size the image.
White and black
If you have a white background or a light sky in your image you can get an idea of how white your white is by laying it against a white background. You can compare the whiteness and adjust as necessary. The same applies to your black tones. Lay your image against a black background to assess the blackness. There are many black and white tones. An image containing white areas may come across as grayish and give a dirty impression. You can adjust the whiteness via: Image – Adjustments – Curves. When adjusting your whites in curves, you maintain good knowledge of all other information in the image. There are many ways to adjust white tones in Photoshop. Play around to find the best method for you.
The right color working spaces is important
Color working spaces is an area with a color interpretation that is used in color systems to standardize colors, to be able to indicate a specific color. Color working spaces need to be communicated between photographers and printers to ensure that the photographer gets the exact color in their image when printed. For printers to be able to do your images justice, the colors must lie in the CMYK (four color) color model. In addition, you can create an ICC profile for the particular printer or screen on which your image is to appear.
Rectangular image at 100 MB (approx. 7250 x 4833 px) sufficient for approx:
178 x 127 cm 100 ppi
89 x 64 cm 200 ppi
59 x 42 cm 300 ppi
44 x 32 cm 400 ppi
Square image at 125 MB (approx. 6610 x 6610 px) sufficient for approx:
168 x 168 cm 100 ppi
84 x 84 cm 200 ppi
56 x 56 cm 300 ppi
42 x 42 cm 400 ppi
HD format, screen (such as large slideshows):
1920 x 1080 px (may even be 1280) approx. 6-7 MB
Resolution for different end products approx:
100 ppi facade advertisement, large tapestries
200 ppi newspaper
300 ppi magazine prints, brochures, etc
400 ppi art prints