Digital Images - Computerphile 

I just want to say this guy explains everything extreamly well and clear, really good!

I like to watch all your videos. One suggestion; if the show is a conversation between the camera man and the host. Please give the cameraman his own microphone. Then all of us can understand what the cameraman is saying. OK. For me all I can do is guess.

I like that guy. He manages to keep my attention but also go beyond the most basic explanation

Sorry Linus, you've been out done...

If it's not already planned, you should do a video on the jpeg compression. I learned that in design school and I think it would interest a lot of computerphile/numberphile viewers.

The birth of a legend

This video is quite applicable to what I'm learning now, I found it very interesting! Thank you!

4:34, someone in the background breaking a plate? :P

Ah, the pseudo-2D-array index formula. I figured out how to generalise it to higher dimensions when I was at uni. For 3D it's: i = width*height*z + width*y + x For 4D it's: i = width*height*depth*w + width*height*z + width*y + x In general, each coordinate is multiplied by the product of all the lower-dimensional sizes and the results are added. The only time the highest-dimensional size gets used is in your boundary check code to make sure you're not asking for a location outside the array. Pseudo-n-dimensional arrays are a handy way of circumventing programming language limitations on passing arrays to functions. When faced with a language requiring fixed sizes for all dimensions after the first (I recall C being such a case), you can instead pass a linear array (technically a pointer to one) and a few size integers and use some simple maths in the function body to work with arbitrary sizes of multi-dimensional arrays.

Can you please make a video or a series of videos about file formats, more about how files are stored, and how the bytes of each file are laid out in memory? Kind of like this lecture, but also for different file formats, such as images, videos, audios, pdfs, zip, tar, etc. Some possible topics to discuss would be different file headers and metadata of each file format, and the lay out of data in the actual file. That would be very interesting and informative. What makes a file a file?

3:03 The internet ruined my mind

Absolutely amazing!

would love a video about different image compressions, and what their basic ideas are, also how some audio codecs work in principles would be cool

Turns out it's not that complicated.

I would love to see a follow up of this video, maybe explain a bit more about the most popular formats

The brighter than full scale colors are probably used when editing these videos in so called "video levels" range which has a small headroom to contain overbright values, and impossible colors like 'saturated white', where details can be recovered from with contrast/curves if needed.

Could you please get a second microphone? I cannot hear the questions.

Please do "discrete cosine transform" of the jpeg images. So so good

this made me think of the pictures going around a couple of years ago that had malicious code written into them, that executed when whindows loaded a preview of them.. would be interesting to have some kind of exxplanation on how that worked. was it metadata or what?

Guys, it's pronounced "gif" ;)

GIMP is an awesome for photo editing. This video was really interesting thanks for making it. :-)

These are raster images there are also vector images witch work pretty much how you would construct a shape on a graph in maths. Though I'm not sure on the details of how these are stored on a computer. Vector images are very useful for something you might want to have resized often as they don't lose quality as you make them bigger.

May I suggest a video on how different file types record/interpret/compress/whatever the image?

There's an error in the very last bit. In order for it to be correct you needed to start with 0 and not with 1. So the correct formula for starting with 1 would be (y-1)*stride+(x-1) +1

What would you want padding for? Not criticising or anything, just curious.

So how do you access the red color exactly?! Or blue?

Will there be anything about bump/normal mapping?

Why index an image as a 1d array? Why not a 2d matrix where perhaps the x, y point in the matrix corresponds to the cartesian location of the pixel in the image? Or perhaps keep the location as a 1d array, and use the second to index the channels? Is this not as efficient?

i believe this is the first video where Mike appears?

Technically, alpha is alpha :) It has no intrinsic meaning, but can be (and usually is) used for blending, so people assume it's for transparency. You often get an alpha channel whether you want it or not for optimal memory alignment.

Very cool.

I could keep watching these videos, yet it won't make me a better photographer.

Could you please do the explanation for audio? From low quality mp3 to master file, how different can it be?

C++ example (with no error checking/prevention). struct RGBA8 // an 8bit per channel pixel with alpha channel. { unsigned char r, g, b, a; }; struct Image // an image of RGBA8 pixels { int width, height; // "stride" and number of rows. RGBA8 *pixels; // all the pixels in the image as one long "list" ("array"). RGBA8 getPixel(int x, int y) // returns the RGBA8 at location (x, y) in the image. { return pixels[y*width+x]; } };

Interesting stuff... I'm not too sure on that formula, though (and I have done per-pixel image processing stuff before). To me, it should be something like _(width * stride * y) + (x * stride)_. Unless I've misunderstood what "stride" is referring to?

If I converted RGB image file to header files in c language and then can I do some operations on it? If yes than how?

It could have been explained better, as some non-tech people will be confused with all this bits and channels and tech people already know how basic color information is stored.

Did something break at 4:35?

how about Vector images? How do they work?

It is not Brady's voice at the background, or is it?

7:42 That's a neat trick.

Sir could you please tell me how the images stores in memory actually in deep and how digital data of array stores in memory ?. Please Sir...

what if we took bits from a file, like a music file, then we create a picture with it? how it would look like?

and when you "liquify" a picture in photoshop whats going on behind the scenes?

Am I missing something or formula should be p=(stride-1)*y+x

6:30 look at is hand. that is a smooth as fuck cut.

If every pixel is encoded in 3 channels (r/g/b), black would be every value of these channels 0 and white would be every channel on their max value... but what would be grey or "darker red" / "red mixed with white"? If I experiment in a Image editing software I usually could measure the r/g/b values of a pixel but also the "brightness" where even if red is on its max. value (like 255) if I set it's brightness to 0 it still would be black.

I would have liked seeing an explanation of that padding-thing.

So, he mentioned the special rules for greyscale images, how instead of having each pixel tell all three values it only tells one in grey. Well, couldn't this logic work the same for monochrome images? Couldn't you give each pixel "grey" values, and then specify the universal hue in the header?

I had difficulty hearing the questions. Perhaps this could be improved in future videos. Also, the speaker didn't explain some terms, like alpha channel. Maybe they were explained on a previous video that I missed.

I need subtitles..

To me you'll never beat the original bitmap format. It even had compression, not that anyone used it....

Update the information about digital image capture video..

p = y * width + x x = p mod width y = p \ width

After learning that you can make an image grayscale if you average r,g,b i wrote a small python script to test it: from PIL import Image im = Image.open("your_image") x,y, = im.size img = im.load() for x1 in range(0,x): for y1 in range(0,y): r,b,g = img[x1,y1] avrg = (r+b+g)//3 img[x1,y1]= (avrg,avrg,avrg) im.save("grayscale.jpg","JPEG")

Sean, if you are going to do a bit of talking in the video, you should also wear a mic so we can hear you properly

Why is it that the X value is on the Vertical axis and the Y value is on the Horizontal axis, when in normal graphing it is the opposite?

Huh, just noticed that the new auto-play pauses when you're down in the comments.

i miss the old vga standard 256 color palette standard. A color picture with 1 byte per pixel.

How about *.gif* animated format?

Nooooooooo!!!! SO close to understanding what stride is. If I have a 12-bit (i.e. 16 bpp (bits per pixel)) monochrome 1280 x 800 image sensor and need to convert that to an 8-bit monochrome image, what is the stride? Is it simply the width? Width * bpp (i.e 20,480)? Width * Bytes per pixel (i.e. 2,560)? Or something else? I can't get my output images to look right. They are indeed 8-bit monochrome, but there are artifacts. Upon close inspection, it seems there are 1 pixel wide vertical bands of 0-value in my image, and indeed when inspecting the buffer in memory whilst debugging, every other byte is 0x00. It seems the LSBs are getting truncated by the imager or something, but still ending up in memory. How do I address this? This actually seems like it may not be a stride issue. I'm working with a C#.NET app.

4:34 what happened?!

How old is Mike?

Greet to see a lefty geek

Submission fro future episodes: Zero knowledge proof

holy shit GREAT channel ! SUBBBBBBBBBBBBBBBBBBBBBBB£D

I am constantly amazed how many apparently intelligent people cannot pronounce "th". (And why do university educated people commence an idea or sentence with the linking word "so" - this chap is not the only computerphile presenter who does this)

These videos are great, thanks, but imo you'd gain a lot by giving the guy asking the questions a microphone as well. Can't really hear him so lose some of the explanation.

Can anyone tell me what accent this guy has? I noticed that his th's and his r's are labiodental.

In no point of the video have you even mentioned the word bitmap. 3:50 . "Even brighter red" is very useful for HDR rendering. It is actually very common.

Anyone after multi dimensional data

I still don't understand how pixels are represented by binary code and electrons and then stored.. like where? How? My phone has 100s of pics and videos of moments in time that have now forever past. How tf do they just stay there for me to look at whenever I want. Same with this comment. It's now going to exist even when I die (unless deleted)

"JIFF"!!!!

8 bit color would be allocated as R-G-B 2-2-3 (or similar, whichever you'd like to have the extra bit). Same would be for 16-bit depth graphics, with 5-5-6 or similar, or 4-4-4 plus alpha. The guy seems to be describing 24-bit color depth.

how about, how something is pronounced depends on the people pronouncing it. If a majority prefers a certain way that becomes the norm. If there is no clear norm. Both are right.

"gives us a snapshot" badump tchhhss

Creepy face reflection in the window.

Sean, Please mic yourself. Your comments are to quiet compared to the person being interviewed.

Couldn't you just do: PR2G45B675, PR3G276B34 P equals pixel R equals red and the number the red value G equals green value b equals blue value And when you get to the end of the first row of pixels just put an E at the end for end of line. You don't even need the comma between each pixel code either. The aim is to represent each pixel number with the least amount of characters as possible. Or you could use an x and y location code to tell you which color it is based off a color wheel that it would reference when opening the file. For example PX125Y23, PX46Y234 That's two pixels and the exact color the program will understand the xy code to draw up the image, it will reference a color wheel or square with millions of combinations of x and y to choose the color from like GPS coordinates it will tell the program where to find the color of that pixel off a color wheel or square.

SubTitles please ...

fist.

You need another microphone.

8 minutes of waffling

First! Sorry I had to :(

I can understand my grandparent mispronouncing gif but an "Image analyst" ? Really ??