Html canvases have max sizes depending on device/browser. Eg some mobiles have roughly a 1000x1000 canvas max. What about images stored in memory? Can these be up to the ram of the phone/pc? Can you 'drawImage' large images to these 1000x1000 canvases where it does auto-cropping? (I don't have a phone to test this even for a specific device.)
The max size of an image object is probably browser or memory dependent.
More to your question...
The image object you draw into the canvas can be larger than the canvas.
This causes the canvas to become a "viewport" into the image.
For example:
Your canvas is 1000x1000.
Your image is 1500x1500.
If you do this then the image pixels will be cropped at x>1000 and y>1000.
// canvas shows image pixels from x=0-999 and y=0-999
drawImage(yourImage,0,0)
If you do this then image pixels will be cropped at x<200 & x>1200 and y<200 and y>1200.
// canvas shows image pixels from x=200-1999 and y=200-1999
drawImage(yourImage,-200,-200)
A mental exercise to see how this works is to imagine a piece of paper with a rectangle "viewport" cut from it. Then move a larger-than-viewport image behind the paper. Only a part of the image will only be visible through the viewport. You can move the image and a different portion of the image will be revealed in the viewport.
Related
I am using imgAreaSelect.js for image cropping.
Suppose there is an image of a 'rectangle' shape in the middle of the picture. On larger screen (desktop) when I select the rectangle shape, imgAreaSelect gives me its width & height (say 250 x 150 ). While on a smaller screen (mobile phone) it gives me width & height (say 100 x 50).
I use canvas to draw the cropped image on. So far I have been using the width & height obtained during selection as the width & height of the canvas. This produces images whose dimensions are bigger for the bigger screen while smaller for the smaller screens.
Is it possible in any way to get an image of a standard dimension whether it's cropped from a larger or smaller screen? If yes then do explain with some codes if possible. Thanks
I have been messing around with some new ideas in Javascript, but I'm not very good at making extremely detailed images in Paint, Paint.NET, etc. The problem is when I have a 64 * 64 image or an 8 * 8 and I want it to display 640 * 640 or 16 * 16; the images get blurry. I've seen many other forums and things were people ask this question or a similar one, but I'm relatively new to this and don't want to make the image larger in photoshop or whatever. On a similar note, can I display only part of an image at one time but have a larger image than shown, so that I don't have to make multiple images of the same thing?
Maybe this CSS attribute on your img helps:
image-rendering: pixelated;
I found it in this blog post:
https://css-tricks.com/keep-pixelated-images-pixelated-as-they-scale/
The reason your images get blurry when enlarged is because it is a rasterised graphic (pixel based image) and not a vector graphic (path based image).
When you try to enlarge the rasterised image, the pixels expand in size too which leads to the lower quality/blurry result (also referred to as 'pixelation').
The difference between vector and raster graphics is that raster graphics are composed of pixels, while vector graphics are composed of paths.
Source: http://pc.net/helpcenter/answers/vector_and_raster_graphics
You can't make it bigger without the picture becoming blurry. You are using a raster image. A raster image is an image that is made up of pixels. a color is assigned to each individual pixel. If you enlarge the picture. Each pixel will just be scaled so that it takes up more space on the screen. This will cause the image to appear blurry.
Here's an example:
rrr
rbr
rrr
"r" is a red pixel and "b" is a blue pixel. The dimensions are 3*3.
If you try to make the dimensions larger than 3*3, lets say 6*6, this happens.:
rrrrrr
rrrrrr
rrbbrr
rrbbrr
rrrrrr
rrrrrr
With the image was enlarged, each pixel just became bigger. In the larger image, each 2*2 square was originally 1 pixel in the original image. Now with this example, the new image wasn't blurry because it was just a square. But if you have a more complex image, it becomes blurry.
To fix your problem, use a vector image. A vector image is different from a raster image. Instead of being made up of pixels, it is made of shapes and lines and stuff like that. Each shape has a width, height, x coordinate, and y coordinate. Some shapes have even more variables. Because of this, vector images can be zoomed in indefinitely without becoming blurry. Sometimes when you zoom in on a vector image the quality even becomes better!
Here's an example:
rrr
rbr
rrr
Again, "r" is a red pixel and "b" is a blue pixel. Let's say this image has a width of 500. But you are zoomed out so far that it appears as a 3*3 square on the screen. In the center of the image is a blue circle. Now it doesn't look like a circle because it only takes up one pixel on the screen. So it looks like square. The circle has a fixed radius. and it is located in the center of the image.
Let's zoom in:
rrrrr
rrbrr
rbbbr
rrbrr
rrrrr
The image still has dimensions of 500*500. It is just zoomed in farther so that it takes up 5*5 on the screen. But the circle looks less like a square and more like a cross. and a 3*3 cross looks more like a circle than a 1*1 square.
The farther you zoom in, the more the image will look like a circle. But since you are using a raster image, enlarging it will result in a blurry picture.
To fix your problem use vector images instead of raster images.
For any form of res-sizing images, you will need a Vector-formatted image.
Vector formats are of the following:
CGM
Gerber format (RS-274X)
SVG
Image File Formats - Wikipedia
Use vector based graphics (svg), not raster bitmaps (jpg, png, gif).
Good thing about SVG is you can add CSS and JS to interact with it in a webpage.
Check this article on how to interface with the SVG
Is it possible to set the width and height of a canvas element and have the existing content scale to fit these new dimensions?
Right now the user uploads an image and my page creates a canvas element containing this image and whose dimensions are the same size as the image. I want to limit the size that I'm working with, however, so here is an example of what I want to have happen:
The user uploads an image that is 1600 x 1200 pixels (Not saved to server)
The data goes right to an html5 canvas object
The canvas height and width are set to 800 x 600 and the image content scales appropriately and then is displayed.
Right now if I set the canvas width and height it just crops the image at those dimension, not resizing as I would like. Thanks!
There are many ways to call drawImage
One is:
ctx.drawImage(image, sx, sy, sw, sh, dx, dy, dw, dh)
Where dx,dy,dw,dh are the destination x, y, width, and height.
If you make dw and dh always 800x600, the image will drawn will always automatically be scaled to 800x600.
Here's a tiny example that will always draw any size image to 800x600 http://jsfiddle.net/jAT8Y/
Another alternative is to use context.scale function. Your image quality will remain better if you use scale.
I'm using Phonegap to allow a user to select a photo from their library, and then edit it.
When I retrieve the photo using Phonegap, I store the image in an html img element that is already on my page:
sourceImage = document.getElementById('smallImage');
sourceImage.style.display = 'block';
sourceImage.src = "data:image/jpeg;base64," + imageData;
Of course, when the photo loads in, it could be larger than the phone screen, so I shrink it down in my img element. I modify the actual img element width and height, not the css properties, and the image is properly displaying on screen (around 288 x 200, rather than the original 1024 x 768). So, my img element is now displaying a picture (as a preview) and when the user advances to the next screen, the image is drawn on a canvas so it can be modified:
sourceImage.onload = function(){
myCanvas.drawImage(sourceImage, 0, 0);
}
The image draws correctly, however, it draws the original 1024 x 768 image retrieved from the library and not the modified, smaller image in the actual img element I am displaying on the page. I'm assuming this is due to the fact that the actual image.src is referencing an image that is 1024 x 768, even though I shrink it down.
I have not found any support for re-sizing images before storing them in phonegap. Does anyone know of way I could modify this image src size so that when I am able to shrink it before drawing it to a canvas? (Please keep in mind the user is loading in pictures on-the-fly from their library. I'd prefer to have a client-side solution, but I've not been able to find one).
when you draw the image on canvas you can specify the destination coords on the canvas an the part of the image your like to draw like this:
context.drawImage(image, source_x1, source_y1, source_x2, source_y2, dest_x1, dest_y1, dest_x2, dest_y2);
So you can draw the image in any size you like...
Having trouble scaling with . It seems to make sense to code up a drawing in canvas to a fixed size (ie 800x600) then scale it for specific locations - but sizing occurs in 4 places: 1) in the context definition (ie ctx.width = 800 2) with ctx.scale; 3) in html with
I can scale it with ctx.scale(0.25,0.25) and use but this doesn't appear right - it seems to want the scale to be proportional.
css sizing simply makes it fuzzy so not a good way to go. Any ideas?
Actually, you can resize a canvas using stylesheets. The results may vary across browsers as HTML5 is still in the process of being finalized.
There is no width or height property for a drawing context, only for canvas. A context's scale is used to resize the unit step size in x or y dimensions and it doesn't have to be proportional. For example,
context.scale(5, 1);
changes the x unit size to 5, and y's to 1. If we draw a 30x30 square now, it will actually come out to be 150x30 as x has been scaled 5 times while y remains the same. If you want the logo to be larger, increase the context scale before drawing your logo.
Mozilla has a good tutorial on scaling and transformations in general.
Edit: In response to your comment, the logo's size and canvas dimensions will determine what should be the scaling factor for enlarging the image. If the logo is 100x100 px in size and the canvas is 800x600, then you are limited by canvas height (600) as its smaller. So the maximum scaling that you can do without clipping part of the logo outside canvas will be 600/100 = 6
context.scale(6, 6)
These numbers will vary and you can do your own calculations to find the optimal size.
You could convert the logo to svg and let the browser do the scaling for you, with or without adding css mediaqueries.
Check out Andreas Bovens' presentation and examples.
You can resize the image when you draw it
imageobject=new Image();
imageobject.src="imagefile";
imageobject.onload=function(){
context.drawImage(imageobject,0,0,imageobject.width,imageobject.height,0,0,800,600);
}
The last 2 arguments are the width an height to resize the image
http://www.w3.org/TR/html5/the-canvas-element.html#dom-context-2d-drawimage
If you set the element.style.width and element.style.height attributes (assuming element is a canvas element) you are stretching the contents of the canvas. If you set the element.width and element.height you are resizing the canvas itself not the content. The ctx.scale is for dynamic resizing whenever you drawing something with javascript and gives you the same stretching effect as element.style.