Image resolution

Image resolution describes the detail an image holds. The term applies equally to digital images, film images, and other types of images. Higher resolution means more image detail.

Image resolution can be measured in various ways. Basically, resolution quantifies how close lines can be to each other and still be visibly resolved. Resolution units can be tied to physical sizes (e.g. lines per mm, lines per inch) or to the overall size of a picture (lines per picture height, also known simply as lines, or TV lines). Furthermore, line pairs are often used instead of lines. A line pair is a pair of adjacent dark and light lines, while lines counts both dark lines and light lines. A resolution of 10 lines per mm means 5 dark lines alternating with 5 light lines, or 5 line pairs per mm. Photographic lens and film resolution are most often quoted in line pairs per mm.

Image resolution on raster displays

Pixel resolution (top) and screen resolution (bottom)

A television or raster image display with 525 scan lines makes a picture with somewhat less than 525 TV lines of resolution. The ratio of lines of resolution to the number of format lines in known as the Kell factor, after Raymond D. Kell, who worked out details of visual resolution in scanned systems at RCA in the 1930s.

Pixel resolution

The term resolution is often used as a pixel count in digital imaging, even though American, Japanese, and international standards specify that it should not be so used, at least in the digital camera field. An image of N pixels high by M pixels wide can have any resolution less than N lines per picture height, or N TV lines. But when the pixel counts are referred to as resolution, the convention is to describe the pixel resolution with the set of two positive integer numbers, where the first number is the number of pixel columns (width) and the second is the number of pixel rows (height), for example as 640 by 480. Another popular convention is to cite resolution as the total number of pixels in the image, typically given as number of megapixels, which can be calculated by multiplying pixel columns by pixel rows and dividing by one million. Other conventions include describing pixels per length unit or pixels per area unit, such as pixels per inch or per square inch. None of these pixel resolutions are true resolutions, but they are widely referred to as such; they serve as upper bounds on image resolution.

Below is an illustration of how the same image might appear at different pixel resolutions, if the pixels were poorly rendered as sharp squares (normally, a smooth image reconstruction from pixels would be preferred, but for illustration of pixels, the sharp squares make the point better).

Resolution in various media

• DVDs have roughly 500 rows (or TV lines, or lines per picture height).
• High definition television has 720 rows or 1,080 lines.
• 35mm movie film is often scanned for release on DVD at 1080 or 2000 rows as of 2005.
• 35mm optical camera negative motion picture film can resolve up to 6,000 columns.
• 35mm projection positive motion picture film has about 2,000 columns which results from the analogue printing from the camera negative of an interpositive, and possibly an internegative, then a projection positive.
• Sequences from newer films are scanned and printed at 2,000, 4,000 or even 8,000 columns, called 2K, 4K and 8K, for quality visual effects editing on computers.

External links

• Cintel: 4K; on a 4000-column film scanning system
• Northlight Film Scanner: On a 8000-column film scanning system
• Luminous Landscape's Res-Demyst]; on why pixel count is not always a good proxy for resolution

See also

• Display resolution
• Raster graphics
• Optical resolution