I need to generate some large graphs whose width and height can go up to millions of pixels in size. Please note that I do NOT want to scale down the image. Each point must represent one pixel.
Now using the Bitmap and Graphics objects, this is very much possible if I split the image into smaller squares but it is painfully slow.
I already calculate the pixel RGB values so was wondering if there is a way to create a byte array with these values and manually save them as an uncompressed BMP format file instead of dealing with the Bitmap class and the drawing functions of the Graphics class.
I am comfortable with unsafe code if that helps to speed up the process.
If you're displaying graphs, why don't you use a technology like SVG that can be rendered on the fly with very little processing power, yet can scale to near-infinite sizes thanks to vector expansion?
(While there is good question if anything will be able to read such files...)
BMP format is very simple - you can write it directly to disk (I'd recommend avoiding building huge file in memory unless you have other reasons to do so). There is a fixed-size header and then (for 24bpp) sequences of colors aligned on some width. Assuming you can pick width you will not even need to add any padding - just rows of colors for each pixel.
Related
Im trying to create a little game with C# and GDI+. For learning purposes I'm trying to avoid as much frameworks etc. as possible. So I have some specific questions to GDI+
Is it possible to fill a region object in GDI with an image?
-If not, is there a manual way for it?
Can you read and set single pixels in a graphics object (not a bitmap)?
Have you got any tips for me to increase overall performance in GDI?
Thanks for any help
Is it possible to fill a region object in GDI with an image?
A region can't be filled, it doesn't store pixels. What you are almost certainly looking for here is the Graphics.Clip property. Assign the region to it and draw the image, it will be clipped by the region.
Can you read and set single pixels in a graphics object (not a bitmap)?
No, the Graphics object doesn't store any pixels itself, it only keeps track of where you draw to. The "device context" in Windows speak. Which can be a bitmap, the screen, a printer, a metafile. Not all of these device contexts let you read a pixel back after drawing (not a printer and not a metafile for example). But no problem of course when you draw to a bitmap.
Have you got any tips for me to increase overall performance in GDI?
There is one crucial one, .NET makes it very easy to overlook. The pixel format of the bitmap you draw to is super-duper important. The most expensive thing you'll ever do with a bitmap is copying it, from CPU memory to the video-adapter's memory. That copy is only fast if the format of the pixels exactly match the format the video-adapter uses. On all modern machines that's PixelFormat.Format32bppPArgb. The difference is huge, it is ten times faster than all the other ones.
Many answers that will detail these points:
Once you have a Region it will limit where pixels are drawn. Use Graphics.DrawImage then
No way to read and only a perverted way to set a Pixel by Graphics.FillRectangle(br, x,y,1,1); The reason behind this is probably that Graphics can not only operate in a Pixel mode but also with various other Units from points to inches and mm..
Use Lockbits. Just one example using one Bitmap. Other common jobs demand locking two (one input one output) or or even three (two inputs and one calculated output) bitmaps..
Know what you invalidate, often only a small part really needs it..
Learn about ImageList, it can't do much but is useful for what it does, that is cache images of one size and color depth
Learn when to use a Panel and when a Picturebox
I am working on images in current application and facing lot of issues like resize image , image quality etc.
I have seen lot of website uploading image with good quality and minimum size length. One thing that i noticed image quality does not loose when increase or decrease the dimensions.
So my question is What will be efficient techniques to handle following issues
Reduce image size length
Resize image dimensions
For example if i want minimum image dimensions should be (width = 800 * height=600) so how can i increase dimensions without respect to image quality and how decrease image dimensions according to ratio.
I am working on asp.net MVC3 C# but your suggestion in any language will be helpful for me.
One thing that i noticed image quality does not loose when increase or decrease the dimensions.
If this is the case, then the image is a vector format, such as SVG - PNG and JPEG images will always lose their quality when you increase the size, since the pixels will be stretched. There's ways you can mitigate that, but no way to circumvent it completely.
If you want to scale an image in Java however with as good a quality as you can reasonably get:
BufferedImage scaled = new BufferedImage(img.getWidth(), img.getHeight(), BufferedImage.TYPE_INT_ARGB);
AffineTransform at = new AffineTransform();
at.scale(2.0, 2.0);
AffineTransformOp scaleOp = new AffineTransformOp(at, AffineTransformOp.TYPE_BICUBIC);
BufferedImage scaledImage = scaleOp.filter(img, scaled);
The key part that determines how the image is scaled is AffineTransformOp.TYPE_BICUBIC, which generally gives the best results (as far as it can, anyway.) C# will no doubt have a similar switch that can be set. The scale factor is given by at.scale(2.0, 2.0);, which will increase length and height by two - if you want to, say, reduce the dimensions by half, use at.scale(0.5, 0.5).
Question:
What is a fast way to scale and/or crop a bitmap provided from a WritableBitmap for display in the UI?
Requirements:
Have Low CPU usage
Handle large images (5 Megapixel, abt 2500x2000 pixels)
Resize and/or crop to the same resolution/area as the UI element the bitmap is displayed in.
Use WPF
Specifically, it must allow a 14FPS 5 Megapixel camera image stream to be displayed in a WPF UI element at full speed.
Update:
I have been able to speed up the drawing quite a bit by painting to a Canvas control using an ImageBrush as follows, where m_bitmap is my WriteableBitmap:
ImageBrush brush = new ImageBrush();
brush.ImageSource = m_bitmap;
brush.Stretch = Stretch.Uniform;
canvas.Background = brush;
I'm now able to get the full 14FPS, though it still using about 20% CPU, so I'm not sure how well it preform if I add another camera or two (the plan is to have 4 or so running).
Another thing I think might be slowing down the drawing is the images are in a mono, Gray8, format, not the standard RGB32 (or is it bgra32 for WPF?) format. If I understand correctly, the image has to be converted to the standard format to be displayed, which would add significant overhead to each frame's drawing time.
Some background:
I'm currently working with a 5 Megapixel, 14 FPS, video camera and am trying to get the frames to render to the screen at full speed. I would like to do this using WPF.
I currently have an example in WinForms that runs full speed for an unscaled image, but (as I would expect) it has major trouble if I set the pictureBox.SizeMode = Zoom;. The example reads raw data directly from the camera stream to a buffer and then copies the data from the buffer into the bitmap set to the PictureBox control. The copy algorithm uses LockBits to speed things up.
I converted that example into WPF, rewriting the parts using Bitmap objects to instead use WritableBitmap objects and an Image control instead of PictureBox. Unforunately this is not able to render the stream to the screen at any decent rate, scaled or unscaled. Both have significant CPU load and very slow updates.
The performance when rendering to the screen is turned off is great. It is able to process the image stream at full speed and resolution while using around 3% CPU and less than 100MB memory.
Note: when I say rendering to the screen is turned off, the WritableBitmap is still being continuously updated, only is not set to the Image control.
I've seen a lot of discussion about getting fast bitmap updating in WPF, but have been unsuccessful in getting it to work at an reasonable speed/cpu load. Also I would like to have the image scaled in such a way that I can see the whole image.
I imagine the key will lie in some sort of scaling/crop combination that needs to be done so that WPF will not try to render(cache?) all 5 million pixels, but only those on the screen, and only at the current screen resolution. I imagine/hope this can be done fairly easily and without too much hit to memory or CPU, but currently have no idea how to do so. I have found the DecodePixelWidth and DecodePixelHeight properties, but those are only applicable when loading an image from a file to a BitmapImage.
Did you have a look at the following post?
Resizing WritableBitmap
If it does not solve your problem, I have more questions for you:
What is the resolution of your image?
Is the size of you UI element constant? What's its size?
Edit:
After your edit, I noticed that you want to display a BitmapImage in Gray8 PixelFormat, why don't you try to set this property when creating your BitmapImage (m_bitmap)?
m_bitmap.Format = PixelFormat.Gray8; // could not test
I am certain that taking your 8 bits/pixel and multiplying the amount of bits needed per pixel by 4 while not gaining any quality is slowing down your application. Especially because you run operations on 32 bits per pixel images when you could be running those operations on 8 bits per pixel images.
While its interface is a bit old-fashioned, I believe that convert (see http://en.wikipedia.org/wiki/ImageMagick) is very often used (and may in fact be the industry standard).
Edit: StackOverflow has about 2,300 question tagged with imagemagick here. See for example What is the difference for sample/resample/scale/resize/adaptive-resize/thumbnail operators in ImageMagick convert?
The OP for https://apple.stackexchange.com/a/41531 decided to go with ImageMagick. And the accepted answer to Efficient JPEG Image Resizing in PHP also suggests ImageMagick, with 19 votes.
However, I don't know whether ImageMagick is capable of meeting your requirements of 14FPS, 5 Megapixels.
The only answer to Recommendation for real time image processing tools on Linux suggests a fork graphicsmagick, which seems to also be available for Windows.
My application is used to design airports for a flight simulator. Users can add one or more images as background. The image(s) can be sized accurately and then used as a template to lay down features such as runways, aprons and so on.
I use a third party graphics library (Piccolo) which has an image class (as far as I can see it is a simple wrapper for System.Drawing.Image).
So far I have done little except allow the user to add an image, size it and so on. It will be no surprise that users sometimes complain of poor performance. We tell them not to load large images (up to 100k seem OK) but don't stop them and 100Mb bitmaps have been used with horrible results.
I need to fix this in a couple of ways. First by converting any image they use to an efficient format (size vs definition) and second by ensuring that the loaded image is suitably sized for the dimensions - at the moment I don't do anything specific to deal with the resizing of say a 2000 x 2000 image to fit a 500 x 500 area of the display.
The default 1:1 display of the application represents 1m per pixel. Once the user has resized the image to fit accurately would I be right in thinking that the best resoultion for the image would be to resample it to that size? I am aware that if the user zooms in way past 1:1 which they will probably do then the clarity of the image will fall.
My ignorance of handling images is complete. I have looked at some image manipulation libraries (ImageMagick and the free version of dotIamge) first for converting the input image to a standard one and second for resizing -resampling. The truth is that they do far more than I need.
Any pointer much appreciated.
Yes, resampling so that the bitmap doesn't constantly have to be rescaled for every paint should make a big difference. The default Graphics.InterpolationMode makes pretty images but is not cheap.
Another biggie is the pixel format of the bitmap. Format32bppPArgb is 10 times faster than any of the others on most video adapters.
private static Bitmap Resample(Image img, Size size) {
var bmp = new Bitmap(size.Width, size.Height, System.Drawing.Imaging.PixelFormat.Format32bppPArgb);
using (var gr = Graphics.FromImage(bmp)) {
gr.DrawImage(img, new Rectangle(Point.Empty, size));
}
return bmp;
}
I would like to resize a picture to a specific file size. For example, no more than 200KB.
What is the best approach to achieve this with C# .NET ?
Thanks !
If you think about it, you aren't going to know the filesize of the image until after it's resized. So you've either got to perform a successive iteration of attempts and compare the file sizes afterwards or you could change your constraints to restrict images to a particular set of height and width dimensions.
See How to resize an image in C# to a certain hard disk size
If this is not a very important function, trial and error works well enough. Just assume that if you need to shrink the input to N * 100%, you do so by scaling both dimensions by sqrt(N) * 100%.
If it is important, you need to understand image compression technologies better. I'll assume JPG. It's an image format that achievs lossy compression by breaking the image down into 8x8 pixel blocks, DFT transforming them, throwing away small coefficients, and then compressing the resulting bitstream.
Now it follows that you can fiddle quite a bit with the quality level, how many of the small coefficients you throw away. You don't need to redo the (expensive) DFT for this. So if the file ends just slightly too large, you can throw away a few more coefficients and recompress. And if you were slightly to aggressive, then put back a few coeffecients and compress again. This is all fairly fast.
You can do quite alot with the Drawing.Image class in order to resize an image.
There are many questions on how to do that. Here is one.
In terms of the size - you will not know what the size is untill after the resize operation. The only way to be certain is to resize, check the result and if it is too large try resizing with lower quality. Repeat until done.
You can approximate the size if you know the dimensions and color depth, as described in the answers to this (identical?) question.
A rough estimate is as follows:
size(KB) = (width * height * bitdepth) / (8 * 1024)
The file size is inflated a bit more due to file information (compression info, etc).