Answer to this Question?

GhOsT

New Member
#1
Hi this is a extract from a exam that was conducted , i found this question intresting as it has 2 answers , or maybe i am wrong (if i am please correct me)

The resolution of an image was changed from 2048 pixels x 1024 pixels to 1024 pixels x 512 pixels.

What happened to this image?

(A) It was cropped.
(B) It took up less storage space.
(c) Its length and width increased.
(D) It changed from color to greyscale.

Please post your answers and comments
 

Terry60

Knows where his towel is.
Staff member
#3
b.

a's not right because it wouldn't be the same image, just 1/4 of it.
The resolution was changed not the size.
 

JustinW

Super Moderator
Staff member
#4
Yeah... 600x800 may be a resolution, but it possible that displays of different sizes can display it.
 

Terry60

Knows where his towel is.
Staff member
#6
Pick a picture from your folder; for simplicity one that will display full size on your screen, say 800x600.
Preview it, so that it opens full size in photo gallery.
Click on Open in the tool bar and select "Paint" as the editor.
Select Image/Resize in Paint and make horizontal and vertical values 50%
Now select View/Zoom/Custom and 200%.
Drag the Gallery and Paint windows side by side, and you'll see the same picture, same display size, but one, more pixelated, which only takes 25% of the RAM or HDD space.

Take for example, the picture of my desktop in the Water Cooler/Desktop thread. Crop it to 1/4 of the size, and you will have reduced the number of pixels 50% per side and the storage required to 25%, but, its not the same picture. It's one cat, not four.
 

Terry60

Knows where his towel is.
Staff member
#8
Compression's a bit different. That makes use of the fact that adjoining sections of a still picure, or consecutive frames of a video image, are substantially the same as the neighbours, and instead of encoding every pixel in full detail, instructions like "4000 pixels exactly the same as the last one" can save lots of storage without losing any detail (lossless compression). "Lossy" compression like jpg, also says "These pixels are nearly the same as those, so we'll pretend they're all identical and include them in the same block". This saves much more storage, but of course you lose detail from the picture.
 

JustinW

Super Moderator
Staff member
#10
Don't mean to hijack the thread, but this seems like a perfect place to ask.

I recently earned the CompTIA Security+ cert. It seems like they had a few confusing questions on the test that went something like this:

Which type of encryption should be used when storing large chunks of data?

Can't remember all of the choices now, but the ones that made sense were:

1) Assymetric Encryption
2) Symmetric Encryption

Don't even know if I answered it correctly as they do not tell you, but this is something I didn't come across when studying. I would think symmetic would be best because only a private party or parties that have the private key can en/de-crypt the information and that is seen as important since a lot of confidential information could be stored, but then I got to thinking that assymetric would also be a good choice because there are times where you want to distribute it to other parties using a seperate key for decryption. So any thoughts on what the right answer should be?
 

mqudsi

Mostly Harmless
Staff member
#11
Hmmm.. I think it may have been one of the other options, Justin.

To the best of my knowledge, the only special encryption case for large files is that you would prefer to use a chunk-based encryption scheme (not sure of the exact name) so that you can read the first xx bytes and encrypt them on the fly instead of having to read the full file and encrypting it at once.

stream-based encryption, chunk-based, not sure exactly what it's called.

Asymmetric/Symmetric encryption has more to do with how you will use the data rather than what it is.
 

JustinW

Super Moderator
Staff member
#12
Your referring to what is known as a stream chiper. Block chipers encrypt in chunks whereas stream is on-the-fly. Stream chipers as you described might be an advantage due to performance efficency, but I'm thinking more along the lines of security sense that is primarily what the concepts of the test's objectives focus on. Both types can be used in either type of algorithm anyway, so who knows...:??