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steganography

This tag is associated with 8 posts

Visualising 2D Discrete Cosine Transforms

I’m interested in the Discrete Cosine Transform (DCT) method as a means of hiding one image inside another. It’s also a key technique in image compression. I’ve implemented the DCT method on an Excel spreadsheet. The image below is an 8×8 grid of pixel values, in grey ranging from 0 = black to 255 = … Continue reading

Beyond averages: DCT graphics

The visual field is full of smooth curves. Shadows don’t have sharp edges but fade out. Colours blend, sometimes imperceptibly. At some level of detail, most things transition smoothly, but to varying degrees. The variation across such transitions is noticeable in a high quality digital photograph, i.e. a pixel image. Here is a random row … Continue reading

The culture of the GIF

GIF image files have 8 bit colour for red (R), green (G) and blue (B), i.e. 256 shades each for RGB. Most smartphone cameras currently provide 10 bit colour. So if you convert your photographs to GIF format they will be of lower quality. Apart from that the GIF format provides lossless compression. So GIF … Continue reading

Hiding one surface inside another

What’s it like to get inside a surface? I’ve been reading Avron Stroll’s seminal philosophy book Surfaces. He exhausts most of the ways people use the word “surface” in everyday speech. E.g. you can be on a surface or under it, but it’s not usual to speak of a surface inside a surface. And some … Continue reading

Ornament and crime

The Austrian architect Adolf Loos (1870-1933) wrote Ornament and Crime. It is a celebrated polemic against the superfluity of ornament in the modern industrial age: “not only is ornament produced by criminals but also a crime is committed through the fact that ornament inflicts serious injury on people’s health, on the national budget and hence … Continue reading

Steganography for architects

Steganography is hiding one picture (a secret or data) inside another (a host or carrier) image. As with cryptography in general, there are several reasons someone might want to hide content in this way. The hidden image could serve as a digital watermark. That’s to assert your claim on a picture. If someone copies it … Continue reading

How to hide one picture inside another

Here’s an anamorphic image of Karl Marx in the aptly named Karl Marx House in Trier, Germany. Face on, the image is a blur. Side on you can see him. That’s one way of concealing an image, revealed only if you know where to stand. Digital images offer other methods as well. Here’s a fragment … Continue reading

Urbanise rasterise

“Raster” is a suitably old fashioned term suggesting the scan lines of a cathode ray television screen. “Pixel” is more up to date. Pixel images have a privileged relationship with architecture. Much architecture is about the grid. Pixel images provide one means of depicting space, i.e. plans and elevations of buildings, zones, regions, city blocks. … Continue reading

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