There is this options box shown when saving a PNG image from Adobe Photoshop. I always choose 'None'.

What does the 'Interlaced' option do?

Screenshot of window in Windows. Heading reads "PNG Options", subheading: "Interlace". Radiobuttons: None (which is selected), and "Interlaced". Buttons are "OK" (selected) and "Cancel"

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    Would just add (as a web designer) PNG's were the format of choice for web - interlace option is largely mute these days unless you are working for an audience on dial up modems. Originally interlace was a good option as it would load part of the image quickly to soften the user experience i.e. the long wait for page delivery over 56K. This is no longer an issue. And on mobile, you should be avoiding bitmaps and using vectors - which have minimal file size / load in split second/ scale more effectively. And compile them as a font if you can - even better. Commented Jul 31, 2017 at 16:05

2 Answers 2


Interlaced image loads an early degraded version of the whole image as soon as possible and then progressively renders the image to clear state. Interlaced will almost always be a bit bigger in filesize.

Non-interlaced image will load up in tiles showing clear image in each tile as it progresses to load in the image.

  • .gif format follows the same idea.
  • In .jpgformat
    • progressiveis the same as interlaced
    • baseline is the same as not interlaced

GIF Simulation of loading an interlaced png and a non interlaced png using Firefox.

enter image description here

Click to view full size »

The point of the simulation is to show how these two methods look visually when loading the image and not to compare their load times. Interlaced almost always adds a little to the filesize and therefore loads a little slower. There's also the perceived speed that is somewhat subjective. In this simulation, I used GPRS speeds (~7KB/s) and interlaced loaded 3 seconds later. Some people might say it looked like the Interlaced was faster. Some might say it's true, but it looked terrible when the image first started loading in. My personal preference is to not use interlacing.

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    Is there a disadvantage of the interlaced approach, e.g. a larger file size? Commented Apr 9, 2015 at 12:39
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    @Jan-Philip Gehrcke Interlacing does increase the filesize a bit. What you should do is first go with personal preference or use case ( It isn't going to do much on print work ). Then check if interlacing adds too much to the file size and act accordingly. Jpeg progressive is way more efficient and doesn't really affect file size as much.
    – Joonas
    Commented Apr 9, 2015 at 13:01
  • Interlaced GIFs and Progressive JPEGs were very popular on websites in the late-1990s when being on 28.8kbps (or 56K if you're lucky) meant that a large image (e.g. a 50KiB online comic stripimage) would still take over 15 seconds to load, so having a preview that loaded quickly was really valuable. Now it's 2019 and websites have multi-megabyte videos as entire page-backgrounds which load in an instant on my home 1Gbps cable connection. Methinks interlaced images are not long for this world - do modern formats (e.g. WebP) even support it anymore?
    – Dai
    Commented Nov 10, 2019 at 11:07
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    @Dai It's called the "World Wide Web" not the "Western Wealthy Web" in case you forgot. Not everyone in the world has your 1GBps internet connection.
    – Ahmad Alfy
    Commented Sep 27, 2020 at 9:32
  • +1 for @AhmadAlfy. And you don't even need to go to countries that are considered "poor". You can just try to load a web page on mobile while somewhere in the German countryside and you will be thankful for designers who export their images interlaced/progressive.
    – Fred
    Commented Jan 12, 2022 at 12:38

"Interlacing" means that it draws (I'm pulling numbers out of the air) every fifth line (line 5, 10, 15), then every fourth line (line 4, 9, 14), then every third line, etc. until the image is filled in, rather than drawing line 1, 2, 3, 4, 5, etc. in order. This allows a sketchy version of the image to come in gradually and fill in until it's completed. Drawing the lines in order means you get the image from the top down.

Lollero's visual is an excellent demonstration.

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    @Amphiteót I believe there was a user by the name of Lollero who did a really nice graphic illustrating the concept, but that answer has since been deleted. Commented Nov 1, 2014 at 1:08

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