Develop Reference

How to control Excel's scaling of bitmaps

I have a bitmap image and I want to put it in excel. I used this code I found here:
xlWorkSheet.Shapes.AddPicture("C:\\filesystem\\mb2.bmp",
msoFalse, msoCTrue, 0, 0, 518, 390);
But the resulting image is 1.333 times wider and higher. OK, so I can just multiply the dimensions by 0.75 and I get an image in excel with the desired dimensions.
xlWorkSheet.Shapes.AddPicture("C:\\filesystem\\mb2.bmp",
msoFalse, msoCTrue, 0, 0, (float)(518*0.75), (float)(390*0.75));
But that number 0.75 sitting there hard-coded really bothers me. Especially since I've seen this question in which the op's ratio is 0.76. Knowing that this code needs to run on any number of systems with different displays, I want to know how to get the ratio programmatically.
Somewhat also related to this question which has to do with copy-paste without code.

If you are talking about printing, the display is irrelevant.
The dimensions of the image need to be relative to the paper size. The size values in the AddPicture method are in points and are only loosely related to pixels. Points are units if measure that make sense to your printer. The application translates points to pixels for you so you don't need to worry about that.
You can use the InchesToPoints or CentimetersToPoints methods of the Application object to size your image to paper size.

Change resolution with Bit Miracle's LibTiff.Net

I use Bit Miracle's LibTiff.Net to convert scanned image to tiff file, but I want to save images with 200dpi even that scanned with 300 dpi I found this in the Bit Miracle site sample
tif.SetField(TiffTag.XRESOLUTION, img.HorizontalResolution);
tif.SetField(TiffTag.YRESOLUTION, img.VerticalResolution);
but I make this change to set resolution always 200dpi :
tif.SetField(TiffTag.XRESOLUTION, 200);
tif.SetField(TiffTag.YRESOLUTION, 200);
in the tif file property it say 200 dpi but the file size don't change 163 Ko before and after the change,
I make a search for all resolution used in the code, and I make it 200 but always the same file size.
if I change the value in the SetField I got it in the file property but not in the rezolution of the image (same size always for all resolution test)
How I can change the resolution of the destination tif ?

LibTiff.Net is a codec library. It's not designed to resample images.
Changing dpi value will only affect print size of the image, not the image data. You should resample data yourselves.

The difference in image resolution (ppi) between C# and Photoshop

For example, C # says that the selected image contains 96 ppi, while that same image in Photoshop contains 72 ppi.
Why is there a difference?
I’m inclined to trust Photoshop in this case, and how to test image resolution if C# returns false results?
We need to build some sort of validator control that rejects all images with ppi != 300.
Control should support the following formats: jpg, jpeg, gif, png, bmp.
Code is listed below:
Image i = Image.FromFile(FileName);
Console.Write(i.VerticalResolution);
Console.Write(i.HorizontalResolution);

DPI means dots (pixels) per inch. The physical size in inches is subjective, based on the current monitor's size and resolution. Unless you're relying on metadata (which gif and bmp don't contain) you cannot reliably calculate this.
Photoshop simply has a prescribed value for DPI, which it uses when translating images for print. This value is stored in the PSD file and may be copied to JPEG metadata, but if you save the image in a format without DPI metadata, the information is not stored.
Update:
The reason your code gets a different value is that C# fetches its VerticalResolution and HorizontalResolution values from the current DPI setting on the computer. Photoshop's DPI is for use with print, so it knows the physical dimensions if you want to send your image to a printer. It has a default value of 72dpi, but you can change this. The value has no meaning on a screen, though, since screens deal in pixels only.

DPI means dots per inch. A bitmap image does not have an inherent DPI, it merely has a size which is the number of pixels in the horizontal and the number of pixels in the vertical (width and height). An image only gains a resolution (in DPI) when you say how many pixels you want to squeeze into each inch.
So if I have an image that is 100 pixels wide and 100 pixels high (100px × 100px), it will be 100 DPI if I print it (or convert it into a format that dictates the print size) such that it fits exactly in a one square inch (1" × 1"). It will be 50 DPI if I print it to fit in a square that is two inches by two inches, &c.

How can I resize an image in C# while retaining high quality?

I found an article on image processing from here: http://www.switchonthecode.com/tutorials/csharp-tutorial-image-editing-saving-cropping-and-resizing Everything works fine.
I want to keep the high quality when resizing the image. I think if I can increase the DPI value I can achieve this. Does anyone know if this is possible? And if so, how can I implement it in C#?

For starters, it's worth pointing out that there are two general categories of images; vector [e.g. SVG, WMF, Adobe Illustrator and Corel Draw Graphics] and bitmap (also called raster) images [e.g. Bitmap, JPEG and PNG Images].
Vector images are formed from a series of mathematical equations and/or calculations. Bitmap images, on the other hand, are made up of individual dots (pixels) each corresponding to a particular feature on the object the image is taken of.
If it should happen that you want to resize an image, the first thing to consider is if it is a bitmap or vector image. By virtue of the fact that vector images are obtained from calculations, they can be perfectly resized without losing any detail. The case is different for bitmap images. Since each pixel is independent of the other, when you desire to resize it, you are simply increasing or decreasing the source to target pixel ratio.
So in order to double the size of a vector image, simply multiply the target dimensions by two and everything comes out all right. If you should apply the same effect on a bitmap, you are actually increasing each source pixel to cover four pixels (two rows of two horizontal pixels).
Of course, by applying interpolation and filtering, the computer can "smooth" out the edges of the target pixels so they seem to blend into each other and give the appearance of a reasonably resized image but this output is never the same as resizing a vector image; vector images resize perfectly.
You also mentioned DPI in your question. DPI is essentially the number of pixels that correspond to an inch when the image is printed not when it is viewed on a screen. Therefore by increasing the DPI of the image, you do not increase the size of the image on the screen. You only increase the quality of print [which needless to say depends on the maximum resolution of the printer].
If you really desire to resize the image and the image is a bitmap, as a rule of thumb, do not increase the size beyond 200% of the original image's size else you'll lose the quality.
You can see this answer for code to resize bitmap images.
To see a sample vector image, go to this link.
Note Try zooming in and out of the image to see how well it resizes.
A typical bitmap are the StackOverflow sprites. They do not keep their quality resized.
Further Reading
Vector Graphics: http://en.wikipedia.org/wiki/Vector_image
Bitmap Graphics: http://en.wikipedia.org/wiki/Bitmap_image

Simply If the original image is smaller then the re-sized image then there is hardly anything you can do. Rest is a research problem.

This would only be possible if it's a vector graphic. Look into SVG. Otherwise, I think you might need Silverlight or Flex for that part.

What you're asking isn't really possible. You can't enlarge an image while maintaining the same quality.
If you think about an image as a mapped array of pixels (literally, a "bit-map"), this makes sense. The image is saved with a fixed amount of data, and that's all you have to work with when you resize it. Any examples to the contrary (like TV shows, as suggested by one of the comments) are purely fictional.
The best that you can do is set the InterpolationMode property of the Graphics object you're using to do the resizing to "HighQualityBicubic", which is the highest quality smoothing algorithm supported by GDI+ and in fact by every major graphics package on the market. It's the best that even Adobe Photoshop has to offer. Essentially, interpolation means that the computer is calculating the approximate value of the new pixels you're adding to make the image larger from the relative values of neighboring pixels. It's a "best guess" method, but it's the best compromise we've come up with yet.
At the very least, the resulting images won't have "jaggies" or rough, pixelated lines.
Sample code:
Graphics g;
g.InterpolationMode = Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
// ... insert the rest of your code here
Beyond that, it's worth noting that GDI+ (which the .NET Framework uses internally for graphics routines) works best with image sizes that are multiples of 16. So if it all possible, you should try and make the width and height of your resized images a multiple of 16. This will preserve as much of the original image quality as possible.
The ideal solution is to switch to vector graphics that can be resized at will. Instead of pixel information, they contain mathematical information used to draw or "render" the image. Read more on Wikipedia.

let's try metadata in GDI+, may be it can suit your request

How to serve high-resolution imagery in a low-resolution form using C#

Trying to use 300dpi tif images for display on the web. At the moment, when the user uploads an image, I am dynamically creating a thumbnail. If a page is created referencing the high-res image with a width of 500x500px, can I use the same functionality to convert to a gif/jpg on the fly. What is the impending resolution of the jpg that would be created?
EDIT:
To further explain the usage, the user uploads 300dpi images which are approx 3000x3000 pixels. The user is using these images to create a catalog page which will be used for pdf printing. When they are creating the page, we only need 72dpi images to display to the screen, but for print, need the 300dpi images. Obviously they do not want to add a 3000x3000px image to the page, so it needs to be resized to the correct viewing area, e.g. 500x500px etc.

This boils down to a simple image resize. The discussion of DPIs is just ancillary data to calculate the scale factor.
As #Guffa said, you should do this at the time of the upload so that you can just serve static images in your viewer.
This will be a load on the server:
Load the full image. This will be about 27 MB of memory for your 3000x3000 images.
Resize. Lot's of math done lazily (still CPU intensive).
Compress. More CPU + Cost of writing to your drive.
Since you are already taking the time to generate a thumbnail, you can amortize that cost and this cost by not having to repeat Step 1 above (see the code).
After an image is uplaoded, I would recommend spinning off a thread to do this work. It's a load on the web server for sure, but you're only other option is to devote a second machine to performing the work. It will have to be done eventually.
Here is some code to do the job. The important lines are these:
OutputAsJpeg(Resize(big, 300.0, 72.0), new FileStream("ScreenView.jpg"));
OutputAsJpeg(Resize(big, bigSize, 64.0), new FileStream("Thumbnail.jpg"));
We can resize the big image however we need. In the first line we just scale it down by a fixed scale (72.0 / 300.0). On the second line, we force the image to have a final max dimension of 64 (scale factor = 64.0 / 3000.0).
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.IO;
BitmapSource Resize(BitmapSource original,
double originalScale,
double newScale) {
double s = newScale / originalScale;
return new TransformedBitmap(original, new ScaleTransform(s, s));
}
void OutputAsJpeg(BitmapSource src, Stream out) {
var encoder = new JpegBitmapEncoder();
encoder.Frames.Add(BitmapFrame.Create(src));
encoder.Save(out);
}
// Load up your bitmap from the file system or whatever,
// then dump it out to a smaller version and a thumbnail.
// Assumes thumbnails have a max dimension of 64
BitmapSource big = new BitmapImage(new Uri("BigPage0.png",
UriKind. RelativeOrAbsolute));
double bigSize = Math.Max(big.PixelWidth, big.PixelHeight);
OutputAsJpeg(Resize(big, 300.0, 72.0), new FileStream("ScreenView.jpg"));
OutputAsJpeg(Resize(big, bigSize, 64.0), new FileStream("Thumbnail.jpg"));

If I understand what you want - you're trying to make a gif or jpg thumbnail of a very high resolution tif, for web display - if not, I apologize in advance....
If you want the thumbnail to be 500x500px, that is the resolution of the jpg/gif you'll want to create - 500x500, or at least 500x<500 or <500x500 (to fit in the box, unless you want distorted images).
For display on the web, the DPI does not matter. Just use the pixel resolution you wish directly.

Technically the JPG/GIF is created at 72-DPI by the Image classes in .NET. But the DPI really doesn't have any meaning to the browser - it just uses the dimensions 500x500.

When displaying an image on a web, the dpi (or more correctly ppi) setting is irrelevant. It's only the size in pixels that is relevant.
You can convert an image on the fly, but it is very work intensive for the server to do that every time the image is displayed. You should create the sizes that you need when the user uploads the image.