调整图像大小以适合边界框

Question

一个简单的问题，但由于某种原因我今天无法解决这个问题。

我需要在保持纵横比的同时将图像调整为适合边界框的最大可能尺寸。

基本上我在找代码来填写这个函数：

void CalcNewDimensions(ref int w, ref int h, int MaxWidth, int MaxHeight);

其中 w & h 是原始高度和宽度 (in) 以及新的高度和宽度 (out)，MaxWidth 和 MaxHeight 定义了图像必须适合的边界框。

Answer 1

找出哪个更小：MaxWidth / w 或 MaxHeight / h 然后将w 和h 乘以那个数字

说明：

您需要找到使图像适合的比例因子。

要找到宽度的比例因子s，那么s 必须满足： s * w = MaxWidth。 因此，缩放因子为MaxWidth / w。

身高也是如此。

需要最多缩放（较小的s）是您必须缩放整个图像的因素。

Answer 2

根据 Eric 的建议，我会这样做：

private static Size ExpandToBound(Size image, Size boundingBox)
{       
    double widthScale = 0, heightScale = 0;
    if (image.Width != 0)
        widthScale = (double)boundingBox.Width / (double)image.Width;
    if (image.Height != 0)
        heightScale = (double)boundingBox.Height / (double)image.Height;                

    double scale = Math.Min(widthScale, heightScale);

    Size result = new Size((int)(image.Width * scale), 
                        (int)(image.Height * scale));
    return result;
}

我在演员表上可能有点过火了，但我只是想保持计算的精度。

Answer 3

要执行纵横比填充而不是纵横匹配，请改用较大的比率。即把Matt的代码从Math.Min改成Math.Max。

（方面填充不会使任何边界框为空，但可能会将某些图像置于边界之外，而方面拟合不会将任何图像留在边界之外，但可能会使某些边界框为空。）

Answer 4

尝试了 Warren 先生的代码，但没有产生可靠的结果。

例如，

ExpandToBound(new Size(640,480), new Size(66, 999)).Dump();
// {Width=66, Height=49}

ExpandToBound(new Size(640,480), new Size(999,50)).Dump();
// {Width=66, Height=50}

你可以看到，height = 49 和 height = 50 在另一个。

这是我的（沃伦先生的代码的基础版本），没有差异和轻微的重构：

// Passing null for either maxWidth or maxHeight maintains aspect ratio while
//        the other non-null parameter is guaranteed to be constrained to
//        its maximum value.
//
//  Example: maxHeight = 50, maxWidth = null
//    Constrain the height to a maximum value of 50, respecting the aspect
//    ratio, to any width.
//
//  Example: maxHeight = 100, maxWidth = 90
//    Constrain the height to a maximum of 100 and width to a maximum of 90
//    whichever comes first.
//
private static Size ScaleSize( Size from, int? maxWidth, int? maxHeight )
{
   if ( !maxWidth.HasValue && !maxHeight.HasValue ) throw new ArgumentException( "At least one scale factor (toWidth or toHeight) must not be null." );
   if ( from.Height == 0 || from.Width == 0 ) throw new ArgumentException( "Cannot scale size from zero." );

   double? widthScale = null;
   double? heightScale = null;

   if ( maxWidth.HasValue )
   {
       widthScale = maxWidth.Value / (double)from.Width;
   }
   if ( maxHeight.HasValue )
   {
       heightScale = maxHeight.Value / (double)from.Height;
   }

   double scale = Math.Min( (double)(widthScale ?? heightScale),
                            (double)(heightScale ?? widthScale) );

   return new Size( (int)Math.Floor( from.Width * scale ), (int)Math.Ceiling( from.Height * scale ) );
}

Answer 5

以下代码产生更准确的结果：

    public static Size CalculateResizeToFit(Size imageSize, Size boxSize)
    {
        // TODO: Check for arguments (for null and <=0)
        var widthScale = boxSize.Width / (double)imageSize.Width;
        var heightScale = boxSize.Height / (double)imageSize.Height;
        var scale = Math.Min(widthScale, heightScale);
        return new Size(
            (int)Math.Round((imageSize.Width * scale)),
            (int)Math.Round((imageSize.Height * scale))
            );
    }

Answer 6

Python 代码，但也许它会为您指明正确的方向：

def fit_within_box(box_width, box_height, width, height):
    """
    Returns a tuple (new_width, new_height) which has the property
    that it fits within box_width and box_height and has (close to)
    the same aspect ratio as the original size
    """
    new_width, new_height = width, height
    aspect_ratio = float(width) / float(height)

    if new_width > box_width:
        new_width = box_width
        new_height = int(new_width / aspect_ratio)

    if new_height > box_height:
        new_height = box_height
        new_width = int(new_height * aspect_ratio)

    return (new_width, new_height)

Answer 7

超简单。 :) 问题是找到一个你需要乘以宽度和高度的因素。解决方案是尝试使用一个，如果不合适，使用另一个。所以...

private float ScaleFactor(Rectangle outer, Rectangle inner)
{
    float factor = (float)outer.Height / (float)inner.Height;
    if ((float)inner.Width * factor > outer.Width) // Switch!
        factor = (float)outer.Width / (float)inner.Width;
    return factor;
}

像这样将图片（pctRect）适合窗口（wndRect）调用

float factor=ScaleFactor(wndRect, pctRect); // Outer, inner
RectangleF resultRect=new RectangleF(0,0,pctRect.Width*factor,pctRect.Height*Factor)

Answer 8

根据前面的答案，这里有一个 Javascript 函数：

/**
* fitInBox
* Constrains a box (width x height) to fit in a containing box (maxWidth x maxHeight), preserving the aspect ratio
* @param width      width of the box to be resized
* @param height     height of the box to be resized
* @param maxWidth   width of the containing box
* @param maxHeight  height of the containing box
* @param expandable (Bool) if output size is bigger than input size, output is left unchanged (false) or expanded (true)
* @return           {width, height} of the resized box
*/
function fitInBox(width, height, maxWidth, maxHeight, expandable) {
    "use strict";

    var aspect = width / height,
        initWidth = width,
        initHeight = height;

    if (width > maxWidth || height < maxHeight) {
        width = maxWidth;
        height = Math.floor(width / aspect);
    }

    if (height > maxHeight || width < maxWidth) {
        height = maxHeight;
        width = Math.floor(height * aspect);
    }

    if (!!expandable === false && (width >= initWidth || height >= initHeight)) {
        width = initWidth;
        height = initHeight;
    }

    return {
        width: width,
        height: height
    };
}

Answer 9

此任务的 Python 代码基于 Jason 的回答，并修复了使用 img.shape 传递常规参数的放大和参数重新排序。

def fit_within_box(box_height, box_width, height, width):
    """
    Returns a tuple (new_width, new_height) which has the property
    that it fits within box_width and box_height and has (close to)
    the same aspect ratio as the original size
    """
    new_width, new_height = width, height
    aspect_ratio = float(width) / float(height)

    if new_width > box_width or new_height < box_height:
        new_width = box_width
        new_height = int(new_width / aspect_ratio)

    if new_height > box_height or new_width < box_width:
        new_height = box_height
        new_width = int(new_height * aspect_ratio)

    return new_height, new_width