When we talk about image resolution we are basically talking about the quality of an image.
If all the details were sharp and clear even in the smallest detail then we would say that the image had a high resolution.
If fine detail is blurry or appears as blocks of color then the resolution is low.
Digital Images are made up of tiny little blocks of color known as pixels (picture elements). There can be hundreds, thousands, even millions of these pixels in every image and the more pixels in an image the better the detail.
Pixels are arranged in a small grid format, the smaller the pixels the smoother the image appears. If the pixels are too large the picture breaks up and appears more like a mosaic.
The size of the pixels = print resolution. I.e. how big the image can be printed without seeing the blocks of pixels.
* Photoshop is pixel based and as such is resolution dependent!
It depends on the amount of pixels present to accurately recreate the image, which in turn affect how the image can be used. This also can determine which file type is best to use in a paticular situation.
This is in direct contrast to Illustrator which uses vectors not pixels, therefore making Illustrator resolution independent. Another way to think of it is that illustrator is for illustrating and creating images from scratch, where as Photoshop is used to manipulate and edit existing photographic images.
* Note these are suggested guidelines for resolution settings and their uses. Every situation is different so make sure to experiment to see what yields the best results.
A resolution setting of 72 ppi (pixels per inch) is usually best used for images that are only ever going to be used online, electronic media, or some design software such as Power Point. These images will maintain the look and feel you want and load up very quickly.
A resolution setting of 150-200 ppi typically is used for design software like Power Point if you are trying to achieve a sharper image quality *(particularly if your type font looks pixelated) In some cases you may also get a fairly decent print out quality depending on the image itself, the printer used, and the chosen paper stock.
A resoltuion setting of 300 ppi is used when you are trying to get the best possible quality printout.
* If you are working on images for a paticular device remember these are just guidelines, double check to make sure the resolution you choose matches the device you are creating images for.
Digital Image File Types Explained
JPG, GIF, TIFF, PNG, BMP. What are
they, and how do you choose? These and many other file types are used to encode
digital images. The choices are simpler than you might think.Part of the reason for the plethora of
file types is the need for compression.
Image files can be quite large, and larger file types mean more disk usage and
is a term used to describe ways of cutting the size of the file. Compression
schemes can by lossy or lossless.
reason for the many file types is that images differ in the number of colors
they contain. If an image has few colors, a file type can be designed to
exploit this as a way of reducing file size.
Lossy vs. Lossless compression
You will often hear the terms
"lossy" and "lossless" compression.
lossless compression algorithm discards no information. It looks for more
efficient ways to represent an image, while making no compromises in accuracy.
contrast, lossy algorithms accept some degradation in the image in order to
achieve smaller file size.
A lossless algorithm might, for
example, look for a recurring pattern in the file, and replace each occurrence
with a short abbreviation, thereby cutting the file size. In contrast, a lossy
algorithm might store color information at a lower resolution than the image
itself, since the eye is not so sensitive to changes in color of a small
The file types
is, in principle, a very flexible format that can be
lossless or lossy. The details of the image storage algorithm are included as
part of the file. In practice, TIFF is used almost exclusively as a lossless
image storage format that uses no compression at all. Most graphics programs
that use TIFF do not compression. Consequently, file sizes are quite big.
(Sometimes a lossless compression algorithm called LZW is used, but it is not
is also a lossless storage format. However, in contrast with common TIFF usage,
it looks for patterns in the image that it can use to compress file size. The
compression is exactly reversible, so the image is recovered exactly.
creates a table of up to 256 colors from a pool of 16
million. If the image has fewer than 256 colors, GIF can render the image
exactly. When the image contains many colors, software that creates the GIF
uses any of several algorithms to approximate the colors in the image with the
limited palette of 256 colors available. Better algorithms search the image to
find an optimum set of 256 colors. Sometimes GIF uses the nearest color to
represent each pixel, and sometimes it uses "error diffusion" to
adjust the color of nearby pixels to correct for the error in each pixel. GIF achieves compression in two ways.
First, it reduces the number of colors of color-rich images, thereby reducing
the number of bits needed per pixel, as just described. Second, it replaces
commonly occurring patterns (especially large areas of uniform color) with a
short abbreviation: instead of storing "white, white, white, white,
white," it stores "5 white." Thus, GIF is "lossless" only
for images with 256 colors or less. For a rich, true color image, GIF may
"lose" 99.998% of the colors.
is optimized for photographs and similar continuous tone
images that contain many, many colors. It can achieve astounding compression
ratios even while maintaining very high image quality. GIF compression is
unkind to such images. JPG works by analyzing images and discarding kinds of
information that the eye is least likely to notice. It stores information as 24
bit color. Important: the degree of compression of JPG is adjustable. At
moderate compression levels of photographic images, it is very difficult for
the eye to discern any difference from the original, even at extreme
magnification. Compression factors of more than 20 are often quite acceptable.
Better graphics programs, such as Paint Shop Pro and Photoshop, allow you to
view the image quality and file size as a function of compression level, so
that you can conveniently choose the balance between quality and file size.
is an image output option available on some digital cameras. Though lossless,
it is a factor of three of four smaller than TIFF files of the same image. The
disadvantage is that there is a different RAW format for each manufacturer, and
so you may have to use the manufacturer's software to view the images. (Some
graphics applications can read some manufacturer's RAW formats.)
is an uncompressed proprietary format invented by Microsoft.
There is really no reason to ever use this format.
PSP, etc. , are proprietary formats used by
graphics programs. Photoshop's files have the PSD extension, while Paint Shop
Pro files use PSP. These are the preferred working formats as you edit images
in the software, because only the proprietary formats retain all the editing
power of the programs. These packages use layers, for example, to build complex
images, and layer information may be lost in the nonproprietary formats such as
TIFF and JPG. However, be sure to save your end result as a standard TIFF or
JPG, or you may not be able to view it in a few years when your software has
Consider this: Currently, GIF and JPG are the formats
used for nearly all web images. PNG is supported by most of the latest
generation browsers. TIFF is not widely supported by web browsers, and should
be avoided for web use. PNG does everything GIF does, and better, so expect to
see PNG replace GIF in the future. PNG will not
replace JPG, since JPG is capable of much greater compression of photographic
images, even when set for quite minimal loss of quality.
When should you use each?
TIFF This is usually the best quality output from a digital camera. Digital cameras often offer around three JPG quality settings plus TIFF. Since JPG always means at least some loss of quality, TIFF means better quality. However, the file size is huge compared to even the best JPG setting, and the advantages may not be noticeable.
A more important use of TIFF is as the working storage format as you edit and manipulate digital images. You do not want to go through several load, edit, save cycles with JPG storage, as the degradation accumulates with each new save. One or two JPG saves at high quality may not be noticeable, but the tenth certainly will be. TIFF is lossless, so there is no degradation associated with saving a TIFF file.
The TIFF is usually the best file format at a manageable size that ensures a high quality printout
Do NOT use TIFF for web images. They produce big files, and more importantly, most web browsers will not display TIFFs.
JPG This is the format of choice for nearly all photographs on the web. You can achieve excellent quality even at rather high compression settings. I also use JPG as the ultimate format for all my digital photographs. If I edit a photo, I will use my software's proprietary format until finished, and then save the result as a JPG.
Digital cameras save in a JPG format by default. Switching to TIFF or RAW improves quality in principle, but the difference is difficult to see. Shooting in TIFF has two disadvantages compared to JPG: fewer photos per memory card, and a longer wait between photographs as the image transfers to the card. I rarely shoot in TIFF mode.
Never use JPG for line art. On images such as these with areas of uniform color with sharp edges, JPG does a poor job. These are tasks for which GIF and PNG are well suited.
GIF If your image has fewer than 256 colors and contains large areas of uniform color, GIF is your choice. The files will be small yet perfect and are typically used for animation.