Help regarding using the resize API.

[shanji97]

Problem Description

I encountered an issue where I was using scaling an image with where the image with resolution 1427*136 with 600dpi. A setting is present that automatically resizes the image to a maxHeight * maxWidth. The issue was that the image was too small, so I to took the image density and multiplied by scale, which was computed as:

var scale = 1.0f;
bool hasScale = false;
if (maxHeight > 0)
{
  scale = Math.Min(maxHeight / attImage.Height, scale);
  if (scale < 1)
    hasScale = true;
}

The issue was that the image was too small, so I took the image density and multiplied it by scale, which was computed as:

var resizedImage = new MagickImage(attImage);
if (hasScale)
{
  int width = (int)(attImage.Width * scale); 
  int height = (int)(attImage.Height * scale);
  resizedImage.FilterType = FilterType.Lanczos;
  resizedImage.Density = new Density(resizedImage.Density.X * scale);
  resizedImage.Resize(width, height);
}
else if (scaleToOriginalSize)
{
  resizedImage.FilterType = FilterType.Lanczos;
  resizedImage.Resample(attImage.Density.X, attImage.Density.Y);
}
return resizedImage;
}

I don't remember the exact coordinates but the pixel density is reduced from 600 ppi to ~96ppi and the issues regarding the problem of the bigger images is solved, but now I have another problem. Images smaller than 200x100 and with low ppi (26-9ppi) are appearing pixelated. I'd like to make them sharper by shrinking them, but keeping the ppi intact so I don't have to provide new files.
The current image parameters are the following:
Source image: 166100 with 12x12ppi
Upper bounds 200100
The code I am experimenting with:

public static MagickImage ResizeImageField(
  MagickImage attImage,
  float maxHeight,
  float maxWidth,
  bool preservePixelDensity = false)
{
  // If the image is not scheduled for scaling and within bounds and with low pixel density, scale the max width and height, but preserve the density
  bool isImageWithinBounds = maxHeight >= attImage.Height && maxWidth >= attImage.Width;
  if (!scaleToOriginalSize && isImageWithinBounds)
  {
    // Scale the old settings with a custom factor to get the new settings.
    const float scalingFactor = 0.5f; 
    (float newMaxHeight, float newMaxWitdth) = (maxHeight * scalingFactor, maxWidth * scalingFactor);

    return ResizeImageField(attImage, newMaxHeight, newMaxWitdth, false, scalingFactor, true);
  }

  bool hasScale = false;
  if (maxHeight > 0)
  {
    scale = Math.Min(maxHeight / attImage.Height, scale);
    if (scale < 1)
      hasScale = true;
  }

  if (maxWidth > 0)
  {
    scale = Math.Min(maxWidth / attImage.Width, scale);
    if (scale < 1)
      hasScale = true;
  }
  var resizedImage = new MagickImage(attImage);
  if (hasScale)
  {
    int width = (int)(attImage.Width * scale);
    int height = (int)(attImage.Height * scale);
    resizedImage.FilterType = FilterType.Lanczos;

    if (!preservePixelDensity)
    {
      resizedImage.Density = new Density(attImage.Density.X * scale); // should work for the bigger images, than out target bounds.
      resizedImage.Resize(width, height);
    }
    else
    {
      resizedImage.Density = new Density(attImage.Density.X * 1.0)
      resizedImage.Resize(width, height);
    
    }
  }

  return resizedImage;
}

The target image should be 50*83 but 12ppi (anything not pixelated really). I acually don't understand why the code for the bigger images work's flawlessly not so much for the smaller ones. If my scaling algorithm is correct then I guess we have another problem.
When using Affinity Photo, the scaling process is flawless.

[dlemstra]

I don't understand the problem that you are trying to solve. Setting the Density of an image has no effect on the Resize method. What kind of input images do you have?

[shanji97]

The problem I am trying to solve is to prepare an image of a signature, that is going to be inserted on a pdf page. Unfortunately I am not in control I what size and what quality the uploads his/hers signature, so a treshold is established with is a system setting and works for most signatures. The bounds are 200x100. In System.Drawing.Image it was all sorted out, but due to security reasons of the library, I had to rewrite this in this library. Then someone uploaded a rediculously high quality signature as mentioned (1427*136 with 600dpi), the snippet

        resizedImage.Density = new Density(attImage.Density.X * scale);
        resizedImage.Resize(width, height);

apparently solves the issue, but now am stuck on how should I handle images where at least one dimension is below 200x100 with low ppi. I fiddled with Affinity Photo, where i could get the image smaller and sharper, where I can lower the dimension and preserve the ppi, but don't know how do this correctly in code.

[shanji97]

One detail, that i discovered plays a huge role in it, that when dealing with the PDF library, I am sending in the bytes from the Image Magick Lib. When I convert the MagickImage to System.Drawing.Bitmap and specify the exact dimensions to Aspose.Words.Drawing.Shape the smaller images seem fine. I'll test them on other images and share my results.

[shanji97]

I managed to get the image manipulation working with my current, althoutgh I am not sure why this is working. The key to passing the imagebytes from the MagickImage object to the aspose method.

var imageIsOnBounds = resizedImage.Width == imageField.MaxWidth || resizedImage.Height == imageField.MaxHeight;
if (imageIsOnBounds)
  builder.InsertImage(resizedImage.ToByteArray());
else
  builder.InsertImage(resizedImage.ToByteArray(), resizedImage.Width, resizedImage.Height);```

[dlemstra]

Maybe the aspose method is doing some magic when inserting the image? But thanks for coming back and reporting how you resolved your issue.

[shanji97]

Yeah, no problem I still need to share the code for the other issue. As soon as I return to that snippet I post the solution for that part (spoiler: It has also something to do with Aspose).

[shanji97]

Unfortunately my solution is still not as robust as

public static Bitmap ResizeImageFieldBitmap(
  System.Drawing.Image attImage,
  float maxHeight,
  float maxWidth,
  bool scaleToOriginalSize)
{
  var scale = 1.0f;
  bool hasScale = false;
  if (maxHeight > 0)
  {
    scale = Math.Min(maxHeight / attImage.Height, scale);
    if (scale < 1)
      hasScale = true;
  }

  if (maxWidth > 0)
  {
    scale = Math.Min(maxWidth / attImage.Width, scale);
    if (scale < 1)
      hasScale = true;
  }

  var b = new Bitmap(attImage);
  var resizedImage = b;
  if (hasScale)
  {
    double width = attImage.Width * scale;
    double height = attImage.Height * scale;
    resizedImage = ResizeBitmap(b, (int)(width), (int)(height));
  }
  else if (scaleToOriginalSize)
  {
    resizedImage.SetResolution(attImage.HorizontalResolution, attImage.VerticalResolution);
  }
  return resizedImage;
}

public static Bitmap ResizeBitmap(Bitmap b, int nWidth, int nHeight)
{
  Bitmap result = new Bitmap(nWidth, nHeight);
  using (Graphics g = Graphics.FromImage((System.Drawing.Image)result))
    g.DrawImage(b, 0, 0, nWidth, nHeight);
  return result;
}

Where everything seem to be working perfectly. Any other suggestions?

[shanji97]

Ok, so after fiddling with the libraries, I found a confirmed by QA way to do this without any stretching or other glitches.

public static MagickImage ResizeImageField(
MagickImage originalImage,
float maxHeight,
float maxWidth,
bool scaleToOriginalSize,
double targetImageDensity = 96
)
{
  if (scaleToOriginalSize)
    return originalImage;

  // Determine the scale ratio needed to fit within the maxWidth and maxHeight
  double widthScale = maxWidth / (double)originalImage.Width;
  double heightScale = maxHeight / (double)originalImage.Height;
  double scale = Math.Min(widthScale, heightScale);

  // If scaling is needed, ensure it doesn't exceed the original size if scaleToOriginalSize is false

  int newWidth = (int)(originalImage.Width * scale);
  int newHeight = (int)(originalImage.Height * scale);

  // Create a new MagickImage for the resized image to avoid altering the original
  var resizedImage = new MagickImage(originalImage.Clone());

  // Set the filter to use for resizing. Lanczos is usually a good choice, but feel free to experiment.
  resizedImage.FilterType = FilterType.Lanczos;

  // Resize the image using the new dimensions and apply the new density if not preserving the original
  resizedImage.Density = new Density(targetImageDensity);
  resizedImage.Resize(newWidth, newHeight);

  return resizedImage;
}

The Aspose.Words.DocumentBuilder call is builder.InsertImage(image.ToByteArray()).

[dlemstra]

Thanks for coming back and posting this for other people.