My question is about the write times of the RAW and JPEG file formats. A RAW file is larger than a JPEG and needs more time to write to the memory but it does not need to spend time on data compression. A JPEG file is smaller than RAW therefore it takes less time to write to the memory but it requires time to do data compression. From the time the camera shutter button is pressed to the time the picture is completed storing in the memory card, which file format takes less time?
First - do you have a specific problem? The time to dump an image to the memory card varies a lot from camera to camera and the best solution for your problem is probably to try to investigate it yourself.
Also why are you focusing on the time it takes dump the file to the memory card? With the often large buffers of modern cameras you can often continue to take images while the camera processes and saves previously taken ones. The total time required to get the image written to the card is rarely a relevant measure.
To answer your question:
As a general rule the saving of a JPEG is probably a lot faster. Sure RAW files are less processed and can begin to get dumped to the memory card almost instantly but digital cameras that are set to render JPEG with the standard settings usually employ ASIC circuitry for the job. These have vastly better performance than general processors in terms of speed. Fancy picture styles that are not supported by the ASIC processors can therefore take a lot of time to process.
Note that when you increase speed of the memory card and controller (while retaining the same file size) the time to save the image to the memory card decreases to the RAW file's advantage. Imagine for example an infinitely fast transfer speed - an unprocessed file would take no time to get saved while the processed file still has to be processed. This may be a reality if the raw output file size settles in the future and that happens long before the maximum transfer speed possible is reached. I highly doubt that it will though since very few people require the instant dump to memory card feature.
JPEG are almost always faster. The bottleneck is the bus to the memory card, if not the memory card. A faster memory card only shifts the bottleneck from the card to the bus but that will be your limit in terms of speed.
This is because JPEG files are smaller by at least 50% and sometimes much more if you enable on of the lower-quality settings which compressed images even more. The processing of JPEG images takes some time but even RAW files need to be compressed, so it's not like they just bypass the processor.
There are cases when you will see JPEG images take longer and that is when you enable some intense processing options. A number of modern cameras now offer Distortion Correction which is costly and, in my experience, can slow down a camera significantly.
Depending on the camera, some options like Lateral Chromatic Aberration Removal can also be slow but others like Vignetting Compensation are not.
There is not only one factor.
- RAW also have compression (in generally), but lossless, like zip. And depend of entropy (how much different information you have in picture) can produce different files. For example my camera produce from 25MB to 38MB RAW files. High ISO produce more noise and as result bigger files
- JPG files are compressed with loss compression. Here it depend of the level of compression. And again from entropy, because images with high level of entropy can be compressed less. But because of loss compression JPG are usually small, compared to RAW
- One more point about JPG. When camera produce JPG it apply filters, styles and so on on the image which also take some time
P.S. But as general rule you can get: JPG write 1.5 to 2 times faster to the card
I have a Canon EOS Rebel T2i (a.k.a. EOS 550D) which is over 11 (2010) years old. With a Kingston CANVAS React Plus 64GB XCII U3 V90 Micro SD card (very fast, according to reviews).
When I have enabled "Fine" resolution it takes just under 3 seconds from taking the exposure to finish writing to the SD Card.
When I have enabled "Superfine" (18 MP) AND RAW and JPEG files output, it takes 5.56 seconds, per shot and the viewfinder blacks out and reads "BUSY." Unacceptable performance for professional photoshoots.
When in burst mode, it does take around 3 shots per second, but the viewfinder blacks out.
It is a "Prosumer" camera which is showing its age. This is why if one expects Professional performance, you had best step up to the plate and invest accordingly.
Here is a fun exception to the rule that RAW has larger file sizes and thus saves slower since transfer time usually dominates the performance: the Panasonic FZ200 allows you to use "i.Zoom" while saving RAW and/or JPEG. i.Zoom is basically digital zoom up to 2× at the long end of the zoom. When you do that, it saves a full-size JPEG file (with 3/4 of the information supplied by digital interpolation) while it only saves the raw portion corresponding to the visible sensor area fraction. As a result, in this constellation the raw files are smaller than the JPEG files (when saving good quality JPEG). It's sort of an aberration, however, and the successor FZ300 already does no longer allow i.Zoom in connection with saving raw files.
As a rule, raw files can be considered to be larger than JPEG files, and the file size being the main factor determining image saving speed.