I have recently wrote a post titled Photoshop JPEG Settings where I described the various settings for a JPEG image in Photoshop. The settings were available via the Save for Web option in the File menu.
In this post I will discuss the settings that you can change when saving an image as a GIF. There are more options available for a GIF file, mainly because of the limited colours (256) that can be saved in a GIF image file.
There are many options that can be changed when saving a GIF file. I will not discuss all the optoins, but will touch on the more common ones. The GIF settings are as follows:
- Preset This dropdown list provides several quick settings that you can use to apply to your image. There are several JPEG settings listed that include some default options for GIF.
- File Type The dropdown list below and to the left of the Presets list provides a list of all file types that you can save your file as. Selecting GIF will display settings for GIF files.
- Colour Reduction Below the File Type dropdown is a list of options for reducing the amount of colours in the image. The options include:
- Perceptual This option reduces colours by including the colours that are more sensitive to the human eye. The human eye is sensitive to shades of green, so more green will be included if the image contains various shades of green.
- Selective Reduces the number of colours by giving preference to the predominant areas of colour. For example, if you have a picture with a lot of blue sky, and a few trees of green, using this option will include more shades of blue than green.
- Adaptive Unlike the two previous settings, this one chooses most of the colours that closely matches the colours in the original image. If the image contains no pinks or purples, then the colour palette won’t contain these colours.
- Restrictive (Web) There are 216 colours that are considered Web-safe, meaning no dithering will occur when these colours are displayed. Selecting this option will reduce the colours to these 216 colours.
- Dithering Below the Colour Reduction option is the dithering option dropdown. Dithering is the process of concealing the reality that there are fewer colours by displaying colours close together where they meld together to look like a different colour. There are several options in the dropdown for dithering.
- No Dither Does just what it says, doesn’t attempt to blend the colours using dithering. You could end up with a banded image with this option.
- Diffusion The most common, and preferred method of dithering. With this method there is no pattern since the colours chosen to create the missing colour are scattered in the image.
- Pattern This type of dithering has a small impact on file size, in that it makes files smaller. The problem is that it uses a pattern to dither a missing colour, and won’t look as nice as the diffusion dither.
- Noise When you select this option, the dithering is accomplished by creating noise in the image. You may end up with ugly clumps of colours in the image with this option.
- Transparency GIF images have a unique ability to make one colour in the image transparent, meaning the background colour will show through. You also have the option to select the type of dithering to perform to ensure that the transparency blends nicely with the background colour. This option is set in the dropdown below the Transparency checkbox.
- Interlaced This option instructs a Web browser to download the full image in multiple passes. Don’t bother enabling this option as it increases the file size, and makes no difference with the connection speeds in use today.
- Lossy Most people know that the GIF file format is a losseless format, meaning no data is lost when the image is saved. Adobe has included a lossy option that removes additional colours when the image is saved, in addition to those you have removed. Don’t bother with this option as it will affect the quality of your image even more.
- Colors This is where you can select the total number of colours available in the image, from 2 to 256. Some images may not need all 256 colours, so you can decrease the number until you are satisfied with the file size and image. As you decrease the colours you will see the number of colours in the colour table below decrease to represent the remaining colours in the image.
- Dither This option specifies the amount of dither that will be used in the image.
- Matte If you create an image with a specific background colour, and then set that colour transparent the colours will blend to the original background colour. If you want to blend a different background colour, then you can choose it with this option.
- Web Snap The Web-safe colours were briefly mentioned above, and this option is also associated with them. This option determines the percentage of colours in the image that are pushed towards the Web-safe colours.
- Colour Table This table displays a list of all colours included in the image. If you double-click a colour you can select another colour that will replace the selected colour. Below the colours are several options that you can use on the selected colour, such as making the colour transparent, shifting the colour to a Web-safe colour, and locking the colour.
- Image size If you click on the Image Size tab you can resize the image. The options provided here are the same ones provided by Image->Image Size from the Photoshop menu.
That is all the options available for creating GIF images with the Save for Web option. The best way to find the optimal image is to open up four images. Modify the images with different settings to see what works for your image.