Imaging

Before we start to talk about file types is good to know something about color mixing. Two main principles are known in graphics, additive and subtractive. Additive method is used when application uses a light. Model uses red, green and blue color as basic colors which makes white when are joined together. Black color is - no light. By subtractive model the cyan, yellow and magenta colors are used. As these can not form a black color, this one is added as fourth component. White in this case is - no color. Most of digital cameras record the picture as RGRB Bayer color pattern which has to converted in file format that can be recognized by program for screen or print applications.

File format of picture depends a little on what camera gives.  It is good to know what you expect to do with a picture. View it on screen? Print the picture with bubble-jet printer? Print large format?

If you want to work something seriously on graphics, prepare yourself to have a headache of lots of different things like color depth, file format and quality of picture, color space, resolution, picture sizes on different screens, and more and more...

Color depth

File format

The picture could be recorded in one single file format but each of unit reasonably uses it's own file format. For screen applications we need fast loading of picture. In this case the pictures are resampled to smaller sizes and compressed with compression algorithm into JPEG file format. When one color of image is defined as transparent, the image is saved as GIF format. For good quality print the CYMK color model is used so for this purpose the TIFF file format should be prepared. Before picture appears in final shape it is changed by a program which uses mostly it's own file format. Most of better programs supports a work with all of file formats or offer an export tool to make a desired file format. 

In the table below some file types are described.

File formats like  JPEG and TIFF  can save an information of different color depths. On example: picture could be saved in camera as RAW, 12 bit TIFF or even 24 bit compressed JPEG format.  24 bits in JPEG case does not mean bigger color depth but 8 bits per each color channel. When RAW is updated by a computer program like Photopaint or Photoshop, 48 bit TIFF, 32 bit TIFF or either 24 bit uncompressed JPEG can be created. 

Digital camera's file formats

Most of today's customer digital cameras don't offer RAW file format. In the table below you can see some file types that can be created by Dimage 7. Note than this one supports RAW file format too.

As Dimage 7 is not a professional camera, the recording of RAW files has a sense only when you have a good chance to snap a very good photo as converting process takes a lot of time. For convert a RAW into usable TIFF, JPEG, CPT or any of others format I need an afternoon of work for 50 images. By this camera I miss an uncompressed 24 bit JPEG format which encodes all of colors without losing any of color information but the file size is still smaller as RAW or even TIFF. When RAW is converted into other file type, the original color space can be lost if you use color matching.

When picture is used for screen application, the picture size depends on screen size and resolution. Usually for creation of web pages the screen resolution of 72 dpi is recommended, but this is not a good point. In the table below the optimal values of resolution for different screen sizes are stated.

If you intend to create a home page, this values is good to consider to find a best resolution ratio for viewing on different screens. But if you still want to know how larger or smaller will appear the picture on other side of wire, the information of how bigger or smaller will be a picture in other screens.

 Last change 11 december 2001