Bigger File but Less Data?


Today’s Question: You suggested that a TIFF image would not lose significant detail compared to a raw capture [in Friday’s Ask Tim Grey eNewsletter]. But wouldn’t the TIFF file actually have more data? Whenever I’ve created a TIFF from a raw capture the file is significantly larger.

Tim’s Quick Answer: A TIFF file will generally be about three times larger than a raw capture file because the TIFF includes full color information for all pixels. However, even though a raw capture does not include full color information for all pixels, that doesn’t mean the TIFF file would actually include more detail than a processed raw capture is capable of.

More Detail: Most digital cameras only record a single color value (typically either red, green, or blue) for each pixel in the image being captured. On a typical image sensor using the Bayer pattern, for every four pixels there would be one red value, two green values, and one blue value.

When the raw capture is processed to an actual image format, the “missing” information for each pixel is calculated. So, for example, a green and blue pixel value would be calculated for each red pixel, based on the surrounding pixel values. Since the raw therefore only contains one of the three primary color values for each pixel, the file size can be thought of as being one-third of what it normally would for a processed image.

An RGB TIFF image contains full color information for all pixels, so all other things being equal a TIFF file would be three times larger than the raw capture it was derived from. Of course, there are other factors that influence the actual file sizes, such as compression (lossless or lossy) that may be applied to either file format.

Just because the TIFF file is generally about three times larger does not mean it will contain more detail. In fact, depending on the processing and file settings applied to a TIFF image, there may be considerably less detail in a TIFF image compared to a raw capture that is processed with optimal settings.

The bottom line is that you can’t really evaluate potential detail contained within an image purely based on the size of the file. A variety of other factors will also impact the amount of visible detail in a given image file.