JPEG

[Robin Usagani]

So my camera can do 2 types of Large JPEG. one is 15 megapixel with smooth curve logo on it and the other one is with jagged curve logo on it. What is the difference? They both have the same amount of pixels. Can someone enlighten me?

 

[Derrel]

Normally the smooth icon would represent the Larger size...the jagged or stair-stepped logo represents a higher degree of compression. If they are the same number of pixels, that doesn't make much sense....are you sure you've pressed ENTER after selecting a different icon?

Could it represent Maximum, Variable-sized capture, versus Minimum or Space-Saving Size, like Nikon uses? What does the instruction booklet have to say about this?

 

[Overread]

I believe it is just a measure of the compression and quality of the final saving of the data - the MP rating remains the same, but the one with the smooth curve will retain more data and more detail whilst the blocky one will run a higher chance of poorer finer details and background areas are more suseptable to banding.

Generally speaking most people shoot in Large fine (the soft curve) and never shift out of that mode unless they are very pressured for card space.

 

[Robin Usagani]

Derrel, thats what i dont understand. I thought pixel is pixel. They both have the same amount of pixels but they have different MB size? I always thought the size of a jpeg file is determined by the # of pixels.

 

[Derrel]

Derrel, thats what i dont understand. I thought pixel is pixel. They both have the same amount of pixels but they have different MB size? I always thought the size of a jpeg file is determined by the # of pixels.

Oh, pardon my misinterpretation of your OP....I understand what you are saying now. So, the Smooth Curve is the FINE Quality JPEG size, which will use the most storage space, since it will have the lowest level of JPEG compression, probably 1:4.

The jagged- or stair-stepped icon does represent a higher degree of JPEG compression. It will be typically something like 1:10 compressed.

Both images can have the same dimensions in pixels, but would be very different in file storage size,and number of shots per card.

Nikon has an option of recording JPEGs as MAXIMUM Quality, with file storage size being as large,or as small, as is needed based on scene detail, and also has an option to make all the JPEGs use the same,fixed, storage space, thus allowing many,many,many more images to be shot. I was a bit mixed up on your use of the term "same size", as opposed to same pixel dimensions. I do not intimately know the specific Canon you were talking about, so I wanted to ask what the camera instruction book might say,and kind of clarify what you meant by stating that the files were the same "size".

 

[MohaimenK]

It's supposed to be "super fine" jpeg files. I know the old 300D at my work has it and so is the other canon P&S powershot that I have. I think it might be a canon thing.

EDIT Yeah what Darrel said. I guess I was typing as he was typing his message

 

[OrionsByte]

Derrel, thats what i dont understand. I thought pixel is pixel. They both have the same amount of pixels but they have different MB size? I always thought the size of a jpeg file is determined by the # of pixels.

JPEG compression works by not storing every single pixel - basically it stores enough information to allow it to "rebuild" the full image when it's decompressed. Therefore, the more information you store (higher quality), the better the rebuilt image will be. At lower quality levels, you're basically letting the software make an "educated guess" at the missing information, so even though you end up with identical resolution, you lose detail.

This is far oversimplified, but you can think of it like this: if you have a block of 10 red pixels, you can either store the value "red" 10 times (store the value of each pixel), or you can store the value "red" and a value that says to repeat it 10 times. That would be what is called "lossless" compression: all the information is retained, but with less data needed to actually describe it. JPEG compression goes a bit further than this, however, and for example if you had red, orange, and yellow pixels all in a row, it might save just the red and yellow pixels and when you open the file later, it calculates that the most likely pixel color to go between them would be orange.

That's not precisely how it works, but it should be close enough to answer your question. If you want to see it in action, take a couple pictures of the same thing at different quality settings and then view them on your computer zoomed in to 200% or so.

 

[JamesMason]

When it was tested by canon, it was deemed to easy to use. Therefore they added it in to confuse users.

 

[KmH]

I always thought the size of a jpeg file is determined by the # of pixels.

The size of a JPEG file is determined by the scene that was photographed and by which compression ratio you selected in the camera.



Nikons offer 3 ratios:

1. Fine - 4:1 compression
2. Normal - 8:1 compression
3. Basic - 16:1 compression

A very busy scene with a wide variety of tones will result in a larger file size than a very plain scene with few tones.