Basic Question on Image Size

[optical]

This is probably a basic question on Image Size, but I can't find the information on the Forum.

The 10D is a 6 megapixel camera, and taking a Fine resolution Image on JPeg produces 18MB size photo. I assume taking a RAW format will produce even bigger size file. Can someone explain the calculation behind these figures?

I understand that it is possible to increase the image size, and the capacity to print bigger image by interpolation, and there are programs to process it. Is the final image just as good?

[Wilfred]

A 6 megapixel camera will produce 18 Mb UNCOMPRESSED files with 8 bit colors (3072*2048*24 bits = 18 megabytes) or 36 Mb uncompressed files with 16 bit colors (3072*2048*48 bits = 36 megabytes). 16 bit colors is only possible with RAW format, jpeg is always 8 bit.

Hower JPEG and RAW files are compressed. Straight out of the camera large fine jpg's are around 2 Mb and the RAW files are a bit less than 6 Mb.

When you open a jpeg file in e.g. Photoshop and then save as uncompressed tiff, the file will indeed be 18 Mb.

As for your second question: I have no experience with these kinds of programs, but what I do know is that these programs have to 'invent' information in order to increase the image size. The quality will NEVER be as good as a large original, no matter how smart these programs are.

[blinking8s]

i am interested in the answer to the 2nd question, since you can select the dpi and res size when converting to raw...but I have never printed outside the photos original res and 180 dpi...

"cant afford the ink" :( dont get to print much

[Jesper]

As Wilfred already explained, if you have a 6 MP image from the 10D, the uncompressed image data will be 3072 x 2048 pixels times 3 bytes per pixel (1 byte each for red, green and blue) = 18 MB. Different image file formats use different kinds of compression algorithms to make the files smaller.

In JPEG, a lossy compression algorithm is used. That means that some of the finest details in the image are thrown away, which lowers the quality of the image a little bit (how much depends on the compression settings: fine, normal, small). Canon RAW files are compressed with a ZIP-like, lossless compression algorithm.

About your second question: if you want to print big, you can either let the printer or printer driver do the interpolation itself (automatically) or you can do it yourself using special software. The printer or driver will always need to make the image match the native resolution of the printer. Ofcourse, if you blow up your 6 megapixel image to for example 24 megapixels, it's not going to be as good as an image that was originally recorded at 24 megapixels. No software can invent information that isn't there in the original image.

However, if you use special software, you have more control over the way the image is blown up. Also, special software most likely has a better algorithm than your printer or printer driver, so the result will look better.