PHP: imageinterlace

Description

int imageinterlace ( resource image [, int interlace] )

imageinterlace() turns the interlace bit on or off. If interlace is 1 the image will be interlaced, and if interlace is 0 the interlace bit is turned off.

If the interlace bit is set and the image is used as a JPEG image, the image is created as a progressive JPEG.

This function returns whether the interlace bit is set for the image.

User Contributed Notes
imageinterlace

mironto at mironto dot sk
19-Nov-2004 08:17


just to add my 5 cents on the progressive principle of jpeg: there are no several lowres images stored in jpeg along with original picture, the only thing altered is the order of "pixels". in jpeg the image is divided in areas 8x8 pixels, so instead of linear order of pixels (row-by-row), first there is one pixel form each 8x8 area included in the begining of the image data stream, so when the browser recieves all 8x8 area pixels, it can display "pixelate" image and as soon as it recieves more data, the browser can add more pixels and "sharpen" the image.

manuel.warum at edu.uni-klu.ac.at
15-Apr-2004 12:41


About MichaelSoft's note "Imageinterlace($im, 1) creates a JPG which is first loaded completely before showing anything":



Actually, that's not completely true.

This only happens with Internet Explorer (any version, for the time being) as it doesn't seem to support progressive displaying and rather shows the image, when it's 100% done with loading. Other browsers (Mozilla, Mozilla Firefox, Opera, Konqueror, etc.) do their job as they're supposed to do: Displaying a very low-res image, then overlaying a midlow-res image (while loading), and then displaying more and more details.

ben dash xo at dubplates dot org
19-Mar-2004 08:25


There is a bug in Microsoft Internet Explorer (at least at present) that means that often, a progressive/interlaced JPEG will actually NOT show at all whilst loading, suddenly appearing only when the entire picture has loaded. A regular NON-interlaced/NON-progressive JPEG will display line by line as it loads, which paradoxically gives the illusion that it's loading faster. MSIE definitely has this one backwards!!



This behaviour is not apparent in other browsers such as Mozilla/FireFox - in these browsers, the image loads progressively, as it should.

PHPProgrammer
24-Nov-2003 08:21


Using the interlace-option reduces the filesize! (doesnt really match with the idea that an additional low-res-image is stored)