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Relations between Kb and Pixels

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bert
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Relations between Kb and Pixels

Unread postby bert » Fri Nov 20, 2009 1:53 pm

Anybody knows
Is there any relation between Kb and Pixels
Say 15 kb (required in a avatar on the forum) is how many pixels?

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Re: Relations between Kb and Pixels

Unread postby Josh of the Bushveld » Fri Nov 20, 2009 2:04 pm

I think Duco might know more?
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Re: Relations between Kb and Pixels

Unread postby bert » Fri Nov 20, 2009 2:24 pm

I wonder :hmz:

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Re: Relations between Kb and Pixels

Unread postby mfb » Fri Nov 20, 2009 2:52 pm

Hi Bert

The simple answer no not really, because images can be compressed (eg.jpeg) or uncompressed (eg tiff) however there is a relationship because the more pixels an image contains the larger the file size but no exact way to say an image X size will be Y pixels.
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Re: Relations between Kb and Pixels

Unread postby HoepHoep » Wed Dec 02, 2009 4:48 pm

Hi

I believe there is a fixed relationship between pixels and size.
I square pixel equals more or less 2,9 bites.
Therefore an image of say 1835 x 2514 pixels = 4613190 square pixels will be a 13,3 Mb file if it is a .bmp file.

Jpeg are however a compressed format and even at 100% jpeg quality, that same file can be as small as 4,5Mb. I think that the actual image determines the actual compression that Jpeg can achieve and the final file size will therefore vary.

The relationship therefore only apply to .bmp files. I suspect that the RAW files will also follow this rule.
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Re: Relations between Kb and Pixels

Unread postby Sprocky » Wed Dec 02, 2009 6:12 pm

HoepHoep, I may have it wrong, but I disagree.

I work on uncompressed jpeg images that are in the region of 15MB, the same TIFF file is 50MB. The jpeg image will vary in MB depending on colour, contrast and density of the image. The TIFF however will stay constant if the dimensions remain the same.

Yes, very confusing. :doh: :?

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Re: Relations between Kb and Pixels

Unread postby Switchback » Wed Dec 02, 2009 7:47 pm

Another thing to remember is the ammount of colour information each pixel carries. A darker picture has much less information than a well lit or even overexposed picture. I did a quick test now. I took a picture with my camera in RAW. The ONLY thing I did was to almost completely over expose it and save it as a JPEG. I then took the same RAW file and almost completely under exposed it.

The over exposed picture was 4.7MB in file size and the under exposed picture was under 1MB. Both were 4288 x 2848 pixels at 300 DPI.

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Re: Relations between Kb and Pixels

Unread postby Sprocky » Wed Dec 02, 2009 7:51 pm

No relationship between MB and pixels! :thumbs_up:

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Re: Relations between Kb and Pixels

Unread postby Switchback » Wed Dec 02, 2009 8:04 pm

Sprocky wrote:No relationship between MB and pixels! :thumbs_up:


I know and agree with that, been working with pics long enough... :thumbs_up:

Just something interresting I shared.
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Re: Relations between Kb and Pixels

Unread postby HoepHoep » Thu Dec 03, 2009 10:22 am

Sorry guys, you haven't convinced me!

From searching the net the following seems to be the correct answer:
File size = (number of pixels) X (bit depth / 8)

But, this is not true of jpgs.
Remember that a jpg file with max quality settings, ie no compressing, is still a compressed file format! That means that all jpgs are smaller than the above size and always of a lower quality than a raw, bmp or tiff file. jpg-Compression use a complicated algorithm that makes it indeed impossible to predict the file size, even at max quality.

@ Switchback. What was the size of your raw file? Some cameras do 12 bit depth (per channel) raw files and the raw file size for your photo will then be 4288 x 2848 x 12 X 3 / 8 = 54MB. (photo's use red, green and blue (rgb) ie 3 channels)

If you save your raw file as a tiff file the size will be 18MB (tiff uses 8 bit per channel). This will be the size regardless of the colour information of the photo.

jpgs are however totally unpredictable.

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Re: Relations between Kb and Pixels

Unread postby Switchback » Thu Dec 03, 2009 10:47 am

HoepHoep,

I'm quickly looking at two RAW files at the moment. Both are as you said, 12-bit depth and 4288 x 2848 Image Size according to the Metadata. The one file is 11MB and the other 9.73 MB. If my RAW files were round about 54MB each, I'd have to buy a ton more memory cards! :big_eyes:
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Re: Relations between Kb and Pixels

Unread postby HoepHoep » Thu Dec 03, 2009 10:56 am

I am confused :? :D
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Re: Relations between Kb and Pixels

Unread postby Switchback » Thu Dec 03, 2009 11:32 am

Me too... :?

For me it is still about the ammount of information carried in each pixel. Let's use my camera's 12 Bit Image Quality. A bit is either a 1 or a 0, so, a 12-Bit file consists of 12 x 0's or 1's. Thus looking something like this for example: 111001100110

So, a pixle with more 1's than 0's will be larger. So, if all the pixels in a picture contain more 1's than 0's, the file will be larger that a picture who's pixels contain more 0's than 1's?

Or am I talking nonsense now? :hmz:

A bit of a definition about a bit:

"A bit is the basic unit of information in computing and telecommunications; it is the maximum amount of information that can be stored by a device or other physical system that can normally exist in only two distinct states. In information theory, one bit is typically defined as the uncertainty of a binary random variable that is 0 or 1 with equal probability."
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Re: Relations between Kb and Pixels

Unread postby Josh of the Bushveld » Thu Dec 03, 2009 11:42 am

Switchback wrote:Me too... :?

So, a pixle with more 1's than 0's will be larger. So, if all the pixels in a picture contain more 1's than 0's, the file will be larger that a picture who's pixels contain more 0's than 1's?

Or am I talking nonsense now? :hmz:

Yes :) Whether a bit is 0 or 1, it still takes the same amount of 'space'. You can't not have the 0s, else the datum wouldn't make sense.

I think it may have more to do with the range of colours, and how 'busy' the image is. At least this is for JPEGs in my experience.

Try comparing two RAW images, one that is really busy (lots of colours physically close together and one with fewer colours.
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Re: Relations between Kb and Pixels

Unread postby Switchback » Thu Dec 03, 2009 11:54 am

In the days when I still programmed PIC's (Programmable Integrated Circuits), the Memory on my EEPROM IC's (Electrically Erasable Programmable Read Only Memory Integrated Circuits) got fuller much quicker when more 1's were part of the language than 0's. I could view this when converting my code to binary.

So, from an engineering perspective, this makes sense to me that this applies to Digital Images as well. Although both 0's and 1's take up a unit of space, the data ammount of 1's are more than 0's.

Have made the comparison in my previous post.
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