C# – Resize Image to fit in bounding box

algorithmcimage manipulationimage processing

An easy problem, but for some reason I just can't figure this out today.

I need to resize an image to the maximum possible size that will fit in a bounding box while maintaining the aspect ratio.

Basicly I'm looking for the code to fill in this function:

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

Where w & h are the original height and width (in) and the new height and width (out) and MaxWidth and MaxHeight define the bounding box that the image must fit in.

Best Answer

Find which is smaller: MaxWidth / w or MaxHeight / h Then multiply w and h by that number

Explanation:

You need to find the scaling factor which makes the image fit.

To find the scaling factor, s, for the width, then s must be such that: s * w = MaxWidth. Therefore, the scaling factor is MaxWidth / w.

Similarly for height.

The one that requires the most scaling (smaller s) is the factor by which you must scale the whole image.

Related Solutions

Ios – UIImage: Resize, then Crop

I needed the same thing - in my case, to pick the dimension that fits once scaled, and then crop each end to fit the rest to the width. (I'm working in landscape, so might not have noticed any deficiencies in portrait mode.) Here's my code - it's part of a categeory on UIImage. Target size in my code is always set to the full screen size of the device.

@implementation UIImage (Extras)

#pragma mark -
#pragma mark Scale and crop image

- (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize
{
    UIImage *sourceImage = self;
    UIImage *newImage = nil;    
    CGSize imageSize = sourceImage.size;
    CGFloat width = imageSize.width;
    CGFloat height = imageSize.height;
    CGFloat targetWidth = targetSize.width;
    CGFloat targetHeight = targetSize.height;
    CGFloat scaleFactor = 0.0;
    CGFloat scaledWidth = targetWidth;
    CGFloat scaledHeight = targetHeight;
    CGPoint thumbnailPoint = CGPointMake(0.0,0.0);

    if (CGSizeEqualToSize(imageSize, targetSize) == NO) 
    {
        CGFloat widthFactor = targetWidth / width;
        CGFloat heightFactor = targetHeight / height;

        if (widthFactor > heightFactor) 
        {
            scaleFactor = widthFactor; // scale to fit height
        }
        else
        {
            scaleFactor = heightFactor; // scale to fit width
        }

        scaledWidth  = width * scaleFactor;
        scaledHeight = height * scaleFactor;

        // center the image
        if (widthFactor > heightFactor)
        {
            thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5; 
        }
        else
        {
            if (widthFactor < heightFactor)
            {
                thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
            }
        }
    }   

    UIGraphicsBeginImageContext(targetSize); // this will crop

    CGRect thumbnailRect = CGRectZero;
    thumbnailRect.origin = thumbnailPoint;
    thumbnailRect.size.width  = scaledWidth;
    thumbnailRect.size.height = scaledHeight;

    [sourceImage drawInRect:thumbnailRect];

    newImage = UIGraphicsGetImageFromCurrentImageContext();

    if(newImage == nil)
    {
        NSLog(@"could not scale image");
    }

    //pop the context to get back to the default
    UIGraphicsEndImageContext();

    return newImage;
}

How to scale one rectangle to the maximum size possible within another rectangle

scale = min(dst.width/src.width, dst.height/src.height)

This is your approach but written more cleanly.

Best Answer

Related Solutions

Ios – UIImage: Resize, then Crop

How to scale one rectangle to the maximum size possible within another rectangle

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