# Prism
```
Do you have a prism to take a closer look?
```
Image:

You can see is a QR code but filled with some rainbow colors

After some inspection of colors, all the colors in the QR code is in full color

Example:
```
Full red in RGB value is (255,0,0)
Full green in RGB value is (0,255,0)
Full blue in RGB value is (0,0,255)
Full purple in RGB value is (255,0,255)
etc...
```
At first I think one of the color channel when its **0** then means that block should be **black**

After some investigation, I found each block is 22 X 22 pixels

So I wrote a [python script](solve.py) to get the RGB values of each block,

and then save the block to new image when the color channel is 0:

```python
for i in range(21):
for j in range(21):
r, g, b = rgb_im.getpixel((i*22,j*22))
if r == 0:
new_image[0].paste(black,(i*22,j*22))
if g == 0:
new_image[1].paste(black,(i*22,j*22))
if b == 0:
new_image[2].paste(black,(i*22,j*22))
new_image[0].save("red.png")
new_image[1].save("green.png")
new_image[2].save("blue.png")
```
After running the script, use `zbarimg` to get the flag:
```
# zbarimg red.png
QR-Code:InnoCTF{N9GntE
```
But is part of the flag only

Therefore, I get QR for the `green.png` and `blue.png`:
```
# zbarimg green.png blue.png
QR-Code:Pyy5mNT3VvjbpC
QR-Code:HrtIC4lyls3DL}
```
Then I realized its use all color channel (RGB) and combine them

Alternately, you can just use [Stegsolve.jar](https://github.com/eugenekolo/sec-tools/tree/master/stego/stegsolve/stegsolve)

Change the filter to Full red, green and blue:


And `zbarimg` gets the same result:
```
# zbarimg red.bmp green.bmp blue.bmp
QR-Code:InnoCTF{N9GntE
QR-Code:Pyy5mNT3VvjbpC
QR-Code:HrtIC4lyls3DL}
```

# Flag
> InnoCTF{N9GntEPyy5mNT3VvjbpCHrtIC4lyls3DL}

Original writeup (https://github.com/Hong5489/InnoCTF2019/tree/master/prism).