My image manipulation software crashed when I was editing and ended up corrupting the two files. Can you recover them?
author:
Ork
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The challenge's name is interlaced. What is interlacing?
Interlacing is a technique to fill the alternating lines of data in an image, helping to visualize the image before it is completely rendered.
In a normal image we see the first row of pixels, then the second line and so on as the image loads from top to bottom. This means we can't see much about the image until it is fully loaded. If we load every 2nd or 4th line of the image first then fill the remaining gaps, we will get a rough version of the image. (Our brain is very good at filling the gaps).
Interlace is helpful when the file is too large or the user has slow internet connection.
The question says the author was editing and accidentally corrupted two files. Here I think the two image files refer to two QR images. By intuition, I thought that the two images were interlaced.
So I looked for deinterlacing tool on online.
After examining some links, I found a website called G'MIC Online
After uploading the chal.png into that website, I clicked on the button called Select Filter
You will find a list of filters.
After looking into different filters, I clicked on Repair.
Ah! Deinterlace interesting. Let's click on this.
There are two algorithms we can see here, one is standard, another one is motion-compensated
Let's select Motion-Compenstated and render and then download.
We get this image :
After scanning this QR code, we get this r0gr4mm1ng_ch4ll3ng3!}
As there are two images interlaced, this string is probably for one QR image. Let's find the other one.
There is another option called Deinterlace2x. Let's do the same thing as before, render and click on the Download button.
We get this image :
if you scan the QR code you will find this iutctf{r34lly_ju57_4_p
Basically this is the first part of the flag.
So the flag is : iutctf{r34lly_ju57_4_pr0gr4mm1ng_ch4ll3ng3!}