Pixel aspect ratio in Photoshop
The problem is that whenever I try to open some images (.jpg) within Photoshop, I get a warning message telling me that:
Pixel aspect ratio correction is for preview purposes only. Turn it off for maximum image quality.
For those who don’t know or have a vague idea about pixel ratio, here’s what this is all about.
Pixel aspect ratio specifies the ratio of width to height of one pixel in an image. Frame aspect ratio describes the ratio of width to height in the frame dimensions of an image. For example, D1 NTSC has a pixel aspect ratio of 0.9 (or 0.9 width by 1.0 height). It also has a frame aspect ratio of 4:3 (or 4.0 width by 3.0 height).
Some video formats output the same frame aspect ratio, but use a different pixel aspect ratio. For example, some NTSC digitizers produce a 4:3 frame aspect ratio, with square pixels (1.0 pixel aspect ratio), and a resolution of 640 x 480. D1 NTSC produces the same 4:3 frame aspect ratio, but uses rectangular pixels (0.9 pixel aspect ratio) and a resolution of 720 x 486. D1 pixels, which are always rectangular, are vertically oriented in systems producing NTSC video and horizontally oriented in systems producing PAL video.
If you display rectangular pixels on a square-pixel monitor without alteration, images and appear distorted; for example, circles distort into ovals. However, when displayed on a broadcast monitor, the images are correct.
