<img src="media/640x320_image.jpg" srcset="media/640x320_image.jpg 320w, media/640x1280_image.jpg 768w" sizes="(min-width:768px) 768px, 320px">
What is wrong with the srcset and sizes above? The 640x1280_image.jpg always shows, when I make my window small it doesn't change.
I don't understand media/640x1280_image.jpg 768w. Do you really use a 640px wide image, but tell the browser it is 768px wide?
It breaks everything in the srcset algorithm, for sure.
It looks like you want to use Art Direction to have images of different proportions based on the viewport width.
If this is what you want, you need to use <picture>, because srcset alone doesn't provide this.
Related
I have a site where I want some full-width images (they'll be cropped vertically, for a parallax look). I want to I've read a bunch of articles on srcset and sizes and tried a few things, but I can't figure out (a) whether I need to use "sizes" at all, and (b) especially without sizes, how the browser will choose which image to load.
For concreteness, here's an image spec:
<img src="/images/full/2c8n.jpg" srcset="
/images/320/2c8n.jpg 320w,
/images/640/2c8n.jpg 640w,
/images/1024/2c8n.jpg 1024w,
/images/full/2c8n.jpg">
This is in a full-width container div so the image should go edge to edge.
I'd like it to load the smallest one on mobile and the largest one (the /images/full one) on big desktops, but that doesn't seem to be happening. I've seen that it's possible to use x style as well, but I'm not sure how I'd choose which image to use with each scale factor, if that's even the right way to do it. Any idea what I'm doing wrong and what's the proper way to do this?
The documentation is pretty unclear about the sizes attribute. What I've been able to determine is that it only affects what size to render the image, and NOT image selection. So, sizes="(max-width: 500px) 50vw, 100vw" tells the browser:
if the viewport is up to 500px wide, render the image at 50% of the viewport (50vw)
if the viewport is 501px or larger, render the image at 100% of the viewport (100vw)
For the srcset attribute, the browser takes a look at your list of images, guesses at what size the slot is it should fill and then chooses the next size up. So, edge to edge as per your requirement, this is how it would choose which file to use:
Viewport width up to 319px -> /images/320/2c8n.jpg
VW 320px to 639px -> /images/640/2c8n.jpg
VW 640 to 1023 -> /images/1024/2c8n.jpg
VW 1024 and larger -> /images/full/2c8n.jpg
I've also read, but haven't verified yet, that it uses the first image it finds that fits the requirements between the src and srcset tags. The order of the attributes may make a difference. Again, read but not verified.
I have read about this problem quite often so far and it also occurs for my own projects. Here is an introduction of what I have found out so far about the srcset and the sizes attribte.
There are two different possibilities on how to use the srcset-attribute (source w3c: http://w3c.github.io/html/semantics-embedded-content.html#device-pixel-ratio):
Device-pixel-ratio-based selection when the rendered size of the image is fixed
This is a simple and reliable way to use srcset. You simply say: If the device-pixel ratio of the target devicer is bigger than x, display this image with the following higher resolution.
The x descriptor is not appropriate when the rendered size of the
image depends on the viewport width (viewport-based selection), but
can be used together with art direction.
Example:
<img src="/uploads/100-marie-lloyd.jpg"
srcset="/uploads/150-marie-lloyd.jpg 1.5x, /uploads/200-marie-lloyd.jpg 2x"
alt="" width="100" height="150">
Viewport-based selection
This method allows you to display different image sizes depending on the size of your viewport. This is the method you are primarily using within your example.
The srcset and sizes attributes can be used, using the w descriptor,
to provide multiple images that only vary in their size (the smaller
image is a scaled-down version of the bigger image).
Simple example:
<h1><img sizes="100vw" srcset="wolf-400.jpg 400w, wolf-800.jpg 800w, wolf-1600.jpg 1600w"
src="wolf-400.jpg" alt="The rad wolf"></h1>
One step further: Using the sizes attribute
The default for Viewport-based selection and srcset is, that the image always has 100% width (100vw). The sizes attribute is giving the great possibility to tell the browser, how the width of an image is at a certain screen width.
The sizes attribute sets up the layout breakpoints at 30em and 50em,
and declares the image sizes between these breakpoints to be 100vw,
50vw, or calc(33vw - 100px). These sizes do not necessarily have to
match up exactly with the actual image width as specified in the CSS.
The user agent will pick a width from the sizes attribute, using the
first item with a (the part in parentheses) that
evaluates to true, or using the last item (calc(33vw - 100px)) if they
all evaluate to false.
Example:
<img sizes="(max-width: 30em) 100vw, (max-width: 50em) 50vw, calc(33vw - 100px)"
srcset="swing-200.jpg 200w, swing-400.jpg 400w, swing-800.jpg 800w, swing-1600.jpg 1600w"
src="swing-400.jpg" alt="Kettlebell Swing">
Here is the challange where I would be really glad if someone could enlighten me
Can I rely on srcset that a Client always load the correct image? Or is the actually loaded image also depending on processing power and internet connection speed as some people stated? I had complaints about retina devices which load lower resolution images.
How can I use both: Device-pixel-ratio-based and viewport-based selection together? Because for each possible size in sizes, I may want to define a retina image with 200% size as well as a non-retina image.
And furthermore: Does it make sense to use different images within srcset for different viewport sizes or is this a misuse of the srcset attribute? If it is possible to combine device-pixel-ratio-based and viewport-based selection, this should also be possible.
Can I rely on srcset that a Client always load the correct image?
The answer is NO. Moreso, you can never know the dimension of the image the user will upload unless you want to check that with a Javascript code and then restrict the user to upload the right dimension. But that will not be too user friendly.
Again, You might want to implement an algorithm to always resize the image to the particular size you want without distorting the quality, so you don't have to pass different imageurl to the srcset and just use the src attr. This can be an advantage to users with slow internet connection.
Does it make sense to use different images within srcset for different viewport sizes or is this a misuse of the srcset attribute?
The point is how many device Viewport do you want to handle in all. If you specify different image sizes and dimension for different view port, you might not able to target all at once especially when a new device is available that you didn't handle as at the time you were developing.
I have a web page design where the layout size and image sizes are based on em's. For example:
<html style="width:50em; font-size:16pt">
<body>
<p>Lorem ipsum
<img src="..." style="float:right; width:20em">
</p>
</body>
</html>
Because the image size is specified in em's, it is always in lockstep with the text size. Unfortunately, we don't know how many CSS pixels wide an image is. We also don't know how many device pixels wide an image is, which depends on the size of an em, the magnification, etc.
The <img> srcset and sizes attributes appear to be nearly the solution I want. But I'm not sure if it applies to my situation here. I can generate multiple asset sizes, e.g. 320×240, 480×360, 640×480, etc.
I want the web browser to look at the content box for the <img> element, calculate how many device pixels wide it is, and download the most appropriate image from a list of alternatives. How can I do this?
Note: I did read about the srcset x syntax, but it doesn't seem to be the right tool.
Srcset is definitely a great way to approach this. You basically have a number of images you save out for multiple sizes, usually you'll want to have the image be the same width of the element if possible. Then you set the image that you want to use for each screen width.
<img src="image.jpg" alt="Name"
srcset="
/img-2400.jpg 2400w,
/img-1800.jpg 1800w,
/img-1200.jpg 1200w,
/img-900.jpg 900w,
/img-600.jpg 600w,
/img-400.jpg 400w"
sizes = "(min-width: 2400px) 900px,
(min-width: 1800px) 600px,
(min-width: 1200px) 500px,
(min-width: 900px) 500px,
(min-width: 600px) 600px,
400px" />
So /img-2400.jpg 2400w would use /img-2400.jpg when the screen is closest to 2400px wide.
In the sizes attribute, you can also specify if what the image size will be at certain screen sizes as it may not always be 100% of the width of the browser.
So (min-width: 2400px) 900px is telling the browser that when the window is at least 2400px wide, the image will be 900px wide on the screen. So that should be telling the browser to then grab /img-900.jpg when the window is 2400px wide since that image is set to 900w which is the closest to 900px (its exact).
You can still approximately calculate this if you are using em, by multiplying the em you are using by 16 (this may vary depending on browser settings or settings you impose in your css). So if you set your width of an image in css to be 20em, thats 16 * 20 = 320px.
When these are used in combination, modern browsers should be able to detect the best image to grab dependent on the screen size. See browser compatability for srcset here: https://caniuse.com/#search=srcset
Based on Eric Portis's article, this solves the problem:
<img style="width:20em" sizes="20em"
src="pic-1000.png"
srcset="
pic-150.png 150w,
pic-220.png 220w,
pic-330.png 330w,
pic-470.png 470w,
pic-680.png 680w,
pic-1000.png 1000w">
After the web page is loaded, if the most appropriate image changes for some reason (e.g. using zoom to change the device pixel ratio), then Firefox will always change the image to the most appropriate one at the moment. By contrast, Chrome seems to change the image if the new one is bigger, but won't change to a small image unless you reload the page - the image resolution is sticky upwards.
I'm implementing responsive images in a current project, and referenced this post on CSS-Tricks in which he uses the following example:
<img src="small.jpg" srcset="medium.jpg 1000w, large.jpg 2000w" alt="yah">
I used this format in my own project, specifying only width alternates, and interestingly the W3C Validator is telling me:
When the srcset attribute has any image candidate string with a
width descriptor, the 'sizes' attribute must also be present
I realize the spec is evolving, and this might be more of a validator issue, but I can't seem to find a clear answer as to whether this is in fact true. From what I've read, specifying the sources by width should be enough to assist the browser in making the best choice.
In my project, I have a Pinterest-style grid layout, with three columns of images resizing down to one via breakpoints; and I'm also wondering if my sizes markup is correct to this end:
<img src="img/tile-320.jpg"
srcset="img/tile-480.jpg 480w, img/tile-720.jpg 720w"
sizes="(min-width: 768px) 33.3vw, (min-width: 568px) 50vw, 100vw"
alt="srcset test">
Thus, I have three image sizes, with the 320px version as the default/fallback, and after 768px, the grid has three columns; at 568px it has two, and otherwise the column/image can be assumed to fill the viewport width.
My questions, therefore are: (1) Is sizes actually required for the browser when specifying width-based alternate sources? (2) Is my markup using sizes correct in the above implementation?
Is sizes actually required for the browser when specifying width-based alternate sources?
It's not mandatory to specify sizes if you didn't specify browser will take default sizes="100vw"
Is my markup using sizes correct in the above implementation?
For me it looks good, the main use of sizes is to tell the browser how much should be the width of the image on a different resolution.
I want to know how could I start using the HTML srcset img attribute in my mobile apps. Or Is there any other jQuery plugin which helps me to solve image resolution problem.
<img srcset="banner-HD.jpeg 2x, banner-phone.jpeg 100w, banner-phone-HD.jpeg 100w 2x" alt="Banner Image" />
In short, Srcset is a new attribute which allows you to specify different kind of images for different screen-sizes/orientation/display-types. The usage is really simple, you just provide a lot of different images separating them with a comma like this: <img src="image.jpg" alt="image" srcset="<img> <descriptor>, ..., <img_n> <descriptor_n>">. Here is an example: srcset="image.jpg 160w, image2.jpg 320w, image3.jpg 2x"
This is a longer answer which explains things in more details.
Difference between srcset and picture. Both srcset and picture does approximately the same things, but there is a subtle difference: picture dictates what image the browser should use, whereas srcset gives the browser a choice. A lot of things can be used to select this choice like viewport size, users preferences, network condition and so on. The support for srcset is pretty good and almost all current browsers more or less support it. Situation with a picture element is a little bit worse.
Descriptors are just a way to show what kind of image is hidden behind the resource. There are various kinds of descriptors:
density descriptor. srcset="image.jpg, image-2X.jpg 2x"
The display density values—the 1x, 2x, etc.—are referred to as display density descriptors. If a display density descriptor isn’t provided, it is assumed to be 1x. Good variant to target retina displays.
width descriptor. srcset="image-240.jpg 240w, image-640.jpg 640w". I am sure this is self explanatory. The only problem is that by itself width descriptor is not really helpful. Why? read here
size descriptor, which only makes sense if you use width descriptor. srcset="image-160.jpg 160w, image-320.jpg 320w, image-640.jpg 640w, image-1280.jpg 1280w" sizes="(max-width: 480px) 100vw, (max-width: 900px) 33vw, 254px">. The instructions for the browser would look like this: (max-width: 480px) 100vw — if the viewport is 480 pixels wide or smaller, the image will be 100% of the viewport width. (max-width: 900px) 33vw — if the viewport is 480 pixels wide or smaller, this rule will never be reached because of the previous media condition. And 254px is when there is no media condition listed, the length is assumed to be a default value used when none of the other media conditions are met.
Just for completeness will add here that there is an image-set() attribute for a background image in CSS and some other helpful link here
Here is a detailed guide on srcset along with code samples.
srcset allows you to define a list of different image resources along with size information so that browser can pick the most appropriate image based on the actual device’s resolution.
Each comma-separated item in srcset has:
Image URL, e.g. http://ik.imagekit.io/demo/default-image.jpg or relative path /demo/default-image.jpg
An empty space
The actual width of the image or display density:
Either using display density descriptor, for example, 1.5x, 2x etc.
Or, using width descriptors, for example, 450w. This is the width of the image in pixels.
Using display density descriptor
The syntax for display density descriptors is straightforward. srcset provides a comma-separated list of image resources along with display density it should be used, for example1x, 2x etc.
<img src="image.jpg"
srcset="image.jpg,
image_2x.jpg 2x"
/>
Live demo - https://imagekitio.github.io/responsive-images-guide/srcset-density.html.
Using width descriptor
The syntax is similar to the display density descriptor, but instead of display density values, we provide the actual width of the image.
<img src="image.jpg"
srcset="small.jpg 300w,
medium.jpg 600w,
large.jpg 900w"
/>
This lets the browser pick the best image
Using width descriptor allows the browser to pick the best candidate from srcset based on the actual width needed to render that image on that particular display at runtime.
Note that display pixel density is also taken into account by the browser while calculating the required width. 😎
For example, assuming an image takes up the whole viewport width - On a 300px wide screen with DPR 2, the browser will pick medium.jpg because it needs a 300x2=600px wide image. On a 300px wide screen with DPR value 3, the browser will select large.jpg because it needs a 300x3=900px wide image.
Demo - srcset with width descriptor
Let see this in action with a live demo - https://imagekitio.github.io/responsive-images-guide/srcset-width.html.
Here is a good article on the srcset attribute and how to use it. srcet allows you to declare a set of images to be displayed on different viewport sizes. You just have to save and image at different resolutions e.g. banner-phone-HD.jpeg would be the highest resolution.
Exmaple:
<img alt="my awesome image"
src="banner.jpeg"
srcset="banner-HD.jpeg 2x, banner-phone.jpeg 640w, banner-phone-HD.jpeg 640w 2x">
The above would serve banner-phone.jpeg to devices with viewport width under 640px, banner-phone-HD.jpeg to small screen high DPI devices, banner-HD.jpeg to high DPI devices with screens greater than 640px, and banner.jpeg to everything else.
There are also other methods like CSS media queries you can use to produce the same effect.
I am not aware of any JQuery plugins which would help with this.