Does RAW take longer?

[ted_kostek]

A common complaint in reviews of digicams is that it takes the camera

too long to write RAW files while writing JPEGs is faster. Given

that RAW files require no processing whereas JPEGs must first be

compressed then saved, why does it take longer for the RAW?

 

The only thing I can think of is that the rate limiting step is the

writing process, and since JPEGs are smaller the time to convert +

write is still smaller than the time to write the larger RAW file.

 

Except, is it true that RAWs are bigger? They should only have 1/3

the data anyway, right? Only 1 color at each pixel vs 3 at each

pixel in a JPEG.

[jbq]

Raw files are bigger, because the data is compressed with lossless algorithms, and uses the full range of the ADC.

 

An uncompressed raw file is typically half the size of an uncompressed JPEG (12 bpp vs 24), but it's not unusual for JPEGs to be compressed 6x to 10x, whereass raw files typically don't compress much beyong 1.5x (because of lossless compression and because of the high noise in the low-order bits).

[Ed_Ingold]

It's all true! In a D1x, the RAW files are somewhat slower than the JPEG, and approximately twice the size on disk. All of the exposure and color data is contained in the RAW file, it's just stored differently than for a TIFF file. Furthermore, there are 12 bits of data for each pixel instead of 8 for a TIF or JPEG.

 

You can save compressed RAW files, which take 2-3x as long to process as the uncompressed version. You will find objective data for this at www.dpreview.com. Everything's a compromise, including quality vs speed.

[jespdj]

Like the other posters already said: The slowest part in the system is writing to the CF card. So if the file is larger, writing will take more time.

<p>In Canon cameras, the RAW file (CRW) contains not only the RAW data from the sensor, but also an embedded JPEG version of the image. The RAW data indeed only has 1 color per pixel, but it records the full 12 bits instead of 3 x 8 bits per pixel as in JPEG. Also, the compression algorithm used for RAW images is lossless, which means you don't loose image quality, but it can't be compressed as much as JPEG.

[awindsor]

Interestingly the Canon DSLRs buffer the RAW image regardless of the eventual output format. Nikon's new D70 buffers the image in the form that it will eventually be written. The net effect of this is that you get more consecutive shots at the maximum frame rate if you save JPEG and not RAW.