Tiff, PSD, JPEG and more: Not all pixels are created equal

By James, Design Development.

Now, I’d like to try and make sense of the difference between a few different Raster Art image formats. All the art/images discussed here will fall into the Raster category. I’ll only talk about the most common even though there is quite a few that you may run across.

Common formats…

.TIFF or .TIF (originally standing for Tagged Image File Format) is a file format for storing images, is widely supported by  Raster manipulation applications, by publishing and page layout applications, by scanning, faxing, word processing, optical character recognition and other applications. This format has goodlossless compression options and allows for saving with layers.

.PSD (Photoshop Document), Photoshop’s native format, stores an image with support for most imaging options available in Photoshop. PSD format is limited to a maximum height and width of 30,000 pixels.

.PSB (Photoshop Big) format, also known as “large document format” within Photoshop, is the extension of PSD format to images up to 300,000 pixels in width or height. That limit was apparently chosen somewhat arbitrarily by Adobe, not based on computer arithmetic constraints, but for ease of software testing.

Photoshop’s popularity means that the .PSD format is widely used, and it is supported to some extent by most competing software. It would be safer to save the files using .TIF format to ensure ease of use in the competing software.

.JPG or .JPEG(acronym for the Joint Photographic Experts Group which created the standard.) is a commonly used method of lossy compression for digital photography (image). The key word here is “lossy”. This means that it is a data encoding method that compresses data by discarding (losing) some of it. We see JPGs all the time when we look for images on the internet. A JPG image is always compressed in some way and if the original was another format (TIF or Vector) information has been removed.

*example of original image (left) and a highly compressed image (right). Note the “blockiness”.

When saving as a JPG, the program breaks the image up into 64 x 64 pixel areas. An image with lowest compression would save all the colors in the 64 x 64 pixel area, where as the highest compression will reduce all the colors in that 64 x 64 pixel area to the color that is in the very top, left pixel… which is why a JPG looks blocky sometimes; this is an image with a high level of compression. The highest compressed images take up the least amount of space but look the worst.

There are a handful of other file formats that use rasters; GIF, PNG, BMP, TGA, to mention a few. All of which have their merits for specific use. I’ve chosen to focus on these 4 formats here because they’re the most commonly used at a fairly basic level.

Which format is right for you?

Here are a few simple rules to abide by when working with digital files;

  1. If the file was created in Illustrator, start with that file. You can always export to other formats if necessary.
  2. A Raster file embedded into and saved as an Illustrator (.ai), EPS or PDF document is NOT a true Vector document. In fact this is the WORST option because there is not a way to determine the original size of the embedded Raster image.
  3. Use JPGs for emailing and viewing only. Because JPG files are lossy, you are always removing information that might be needed later.
  4. Be sure to choose the LZW compression option if saving your file as a TIF. This is a LOSSLESS form of compression and will save you lots of room on your disk without removing information from the file.
  5. If exporting from a Vector format to a Raster format choose the option with layers AND DO NOT use Anti-Aliasing. These options will ensure your Vector file will look close to it’s original state even though it is now a Raster file.
  6. Also, if exporting from a Vector format to a Raster format choose a resolution of at least 254 DPI/PPI. This will ensure you do not need to scale the image up later (see post “Illustrator or Photoshop?” for discussion of this).
  7. To ensure you can manipulate your file the way you want to, always open the program and chose the File –> Open option and browse to your file. If double-clicking on the file in the folder, you may open the file into a program that is incorrectly associated with the file.
  8. Finally, be mindful of the file extensions (.tif, .psd, .ai, etc.). If these are changed, your file may not open up at all.

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