Resizing Large Resolution Images Producing 1000X1000 Pixels Size When Size Is Set to 500X500 Pixels

rescale images in canvas after resetting it's ratio

After some research and some testing i found the following solution.
I changed the for loop that scales the objects to this:

for (var i = 0; i < objects.length; i++) {
        var previousH = (((objects[i].getHeight() / canvas.getHeight()) * canvasHeightDefault) * PrevHeightRatio);
        var previousW = (((objects[i].getWidth() / canvas.getWidth()) * canvasWidthDefault) * PrevWidthRatio);

        console.log(previousH + " - " + previousW);

        var multiplierSizeH = 1 / PrevHeightRatio;
        var multiplierSizeW = 1 / PrevWidthRatio;

        var onMaxH = objects[i].getHeight() * multiplierSizeH;
        var onMaxW = objects[i].getWidth() * multiplierSizeW;

        objects[i].height = onMaxH * HeightRatio;
        objects[i].width = onMaxW * WidthRatio;

        var multiplierW = 1 / PrevWidthRatio;
        var multiplierH = 1 / PrevHeightRatio;

        var originalStartX = objects[i].left * multiplierW;
        var originalStartY = objects[i].top * multiplierH;

        objects[i].left = originalStartX * WidthRatio;
        objects[i].top = originalStartY * HeightRatio;
        objects[i].setCoords();
    }

This will keep track of the size before and after the scaling which fixes the issue.

Resize an image without distortion OpenCV

You may try below. The function will keep the aspect rate of the original image.

def image_resize(image, width = None, height = None, inter = cv2.INTER_AREA):
    # initialize the dimensions of the image to be resized and
    # grab the image size
    dim = None
    (h, w) = image.shape[:2]

    # if both the width and height are None, then return the
    # original image
    if width is None and height is None:
        return image

    # check to see if the width is None
    if width is None:
        # calculate the ratio of the height and construct the
        # dimensions
        r = height / float(h)
        dim = (int(w * r), height)

    # otherwise, the height is None
    else:
        # calculate the ratio of the width and construct the
        # dimensions
        r = width / float(w)
        dim = (width, int(h * r))

    # resize the image
    resized = cv2.resize(image, dim, interpolation = inter)

    # return the resized image
    return resized

Here is an example usage.

image = image_resize(image, height = 800)

Hope this helps.

How to save PNG file from NSImage (retina issues)

If you have an NSImage and want to save it as an image file to the filesystem, you should never use lockFocus! lockFocus creates a new image which is determined for getting shown an the screen and nothing else. Therefore lockFocus uses the properties of the screen: 72 dpi for normal screens and 144 dpi for retina screens. For what you want I propose the following code:

+ (void)saveImage:(NSImage *)image atPath:(NSString *)path {

   CGImageRef cgRef = [image CGImageForProposedRect:NULL
                                            context:nil
                                              hints:nil];
   NSBitmapImageRep *newRep = [[NSBitmapImageRep alloc] initWithCGImage:cgRef];
   [newRep setSize:[image size]];   // if you want the same resolution
   NSData *pngData = [newRep representationUsingType:NSPNGFileType properties:nil];
   [pngData writeToFile:path atomically:YES];
   [newRep autorelease];
}

How to scale an image down to fit inside a canvas, without distorting the image?

1) Determine which dimension is the one which exceeds the size of the window you want to put the image in. If both exceed the size calculate both factors and use the largest:

width_factor = imagewidth / allowable_width
height_factor = imageheight / allowable_height

2) Scale both the height and the width by the same factor. Eg. if the width is exceeded:

factor = imagewidth / allowable_width

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