Algorithm to resize image and maintain aspect ratio to fit iPhone

Maybe a slightly shorter routine would be:

// Calculate resize ratios for resizing float ratioW = targetWidth / oldWidth; float ratioH = targetHeight / oldHeight;// smaller ratio will ensure that the image fits in the viewfloat ratio = ratioW < ratioH?ratioW:ratioH;newWidth = oldWidth*ratio;newHeight = oldHeight*ratio;

Obviously if the ratio is > 1, then it's enlarging, if < 1 then it's shrinking.

I think the following should give you the idea. It's not in any particular language, but rather a C-like pseudo code.

shortSideMax = 640;longSideMax = 960;function Resize(image){    if (image.width >= image.height)    {        if (image.width <= longSideMax && image.height <= shortSideMax)            return image;  // no resizing required        wRatio = longSideMax / image.width;        hRatio = shortSideMax / image.height;    }    else    {        if (image.height <= longSideMax && image.width <= shortSideMax)            return image; // no resizing required        wRatio = shortSideMax / image.width;        hRatio = longSideMax / image.height;    }    // hRatio and wRatio now have the scaling factors for height and width.    // You want the smallest of the two to ensure that the resulting image    // fits in the desired frame and maintains the aspect ratio.    resizeRatio = Min(wRatio, hRatio);    newHeight = image.Height * resizeRatio;    newWidth = image.Width * resizeRatio;    // Now call function to resize original image to [newWidth, newHeight]    // and return the result.}

The efficiency of this code, or what you have, won't be an issue. The time it takes to actually resize the image will dwarf the time it takes to do a couple of comparisons, two divides, and two multiplies.

Is this a "more mathematical" way to do it? I suppose, in that it collapses your four cases into two. But the approach is essentially the same.

Below, the simplest way I know to keep proportions. Hope it helps.

Javascript

function resize(width, height, maxWidth, maxHeight) {    var ratio = Math.min(maxWidth / width, maxHeight / height);    var newWidth = ratio * width;    var newHeight = ratio * height;    console.log(newWidth + ' ' + newHeight); // Test    // Process resizing...}resize(1280, 1024, 600, 300);

PHP

function resize($width, $height, $maxWidth, $maxHeight) {    $ratio = min(array($maxWidth / $width, $maxHeight / $height));    $newWidth = $ratio * $width;    $newHeight = $ratio * $height;    echo $newWidth . ' ' . $newHeight; // Test    // Process resizing...}resize(1600, 1280, 150, 150);