Maximum image dimensions in a browser/CSS spec?

Question

I want to display a page containing about 6000 tiny image thumbnails (40x40 each). To avoid having to make 6000 HTTP requests, I am exploring CSS sprites, i.e. concatenating all these thumbnails into one long strip and using CSS to crop the required images out. Unfortunately, I have discovered that JPEG files cannot be larger than 65500 pixels in any one dimension. Wary of further limits in the web stack, I am wondering: are any of the following unable to cope with an image with dimensions of 40x240000?

• Internet Explorer
• Opera
• WebKit
• Any CSS spec
• Any HTML spec
• The PNG spec

Edit: the purpose of this is simply to display an entire image collection at once, requiring that the user at most has to scroll. I want the "micro-thumbnails" to flow into an existing CSS layout, so I can't just use a big rectangular image. I don't want the user to have to click through multiple pages to see everything. The total number of pixels is not that great - only twice what would fit on a 2560x1600 display. The total file size of all the micro-thumbnails is only a couple of megabytes. Assuming every image is manipulated uncompressed in the browser's memory, taking 8 bytes of storage per pixel (RGBA plus 100% overhead fudge factor), we are talking RAM usage in the low hundreds of megabytes; not unreasonable for a specialized application in the year 2010. The only unreasonable thing is the volume of HTTP requests that would be generated if all micro-thumbnails were sent individually.

Answer 1

Well, Safari/iOS lists these limits:

• The maximum size for decoded GIF, PNG, and TIFF images is 3 megapixels. That is, ensure that width * height ≤ 3 * 1024 * 1024. Note that the decoded size is far larger than the encoded size of an image.

• The maximum decoded image size for JPEG is 32 megapixels using subsampling. JPEG images can be up to 32 megapixels due to subsampling, which allows JPEG images to decode to a size that has one sixteenth the number of pixels. JPEG images larger than 2 megapixels are subsampled—that is, decoded to a reduced size. JPEG subsampling allows the user to view images from the latest digital cameras.

• Individual resource files must be less than 10 MB. This limit applies to HTML, CSS, JavaScript, or nonstreamed media.

http://developer.apple.com/library/safari/#documentation/AppleApplications/Reference/SafariWebContent/CreatingContentforSafarioniPhone/CreatingContentforSafarioniPhone.html

Answer 2

Based on your update, I'd still really recommend not using this approach. Don't you think there's a reason that Google's image search doesn't work like this?

As such, I'd recommend simply loading images as required via Ajax. (i.e.: When the user scrolls below the currently visible set of images.) Whilst this will use more connections, it'll mean that you can have sensibly sized thumbnails and as a general approach is much more manageable than having to re-generate pre-generated thumbnail image "sheets" on the back-end when a new image is added, etc.