Are long exposure RAW files larger?

[mpasq66]

Try reading a little more carefully.

Try it yourself.

Okay this might be a really stupid question but I was thinking about uses of RAW files. Since the shutter is open longer, sometimes by several factors, does that mean the sensor is collecting more information over a longer period of time? Doesn't that mean the files should be larger? If not, what am I misunderstanding about RAW?

Again....... shooting in raw has - n o t h i n g - to do with the shutter speed.

I don't think that's what he was asking, I think he was asking more or less if a 5sec exposure produced a larger "file size" than a 1/60 sec. exposure.....

Of course it's 4:30 a.m. here and the ambien is kicking in so......

 

[unpopular]

If the 1/60 shutter speed clips as much detail in the shadows as the 5 sec shutter speed clips detail in the highlights, then typically the two files will be comparable.

No. Shutter speed does not affect file size, information does.

 

[xyphoto]

I feel this discussion is useless. High capacity memory cards are cheap these days. Please worry less about the file size and learn more about taking better photos.

 

[unpopular]

I think the issue is the contrary. If my files are smaller than around 15mb, depending on content, my reaction is that I must have messed up the exposure, and I get excited when I see files that are larger than 20mb because I know that they contain a lot of detail.

 

[SCraig]

lemme just give you a quick few reasons why it's a life saver....

if you shoot with the wrong white balance settings....you can fix it, and no one will ever know that it was shot wrong.
if it is under/over exposed, it can fix that too! (not so much if you have some white hot spots, those are tricky)
if your colors look a little dull... you can fix the color's vibrance!
http://www.thephotoforum.com/forum/...ges/255924-raw-v-jpeg-shootout-challenge.html

All of your reasons are based on the assumption that everyone post processes their images. In reality not everyone does. RAW format is only of any value to those who perform post processing on them. To those who shoot strictly out-of-camera there are zero benefits to shooting in RAW format and one major disadvantage, that being that not all image software can properly process RAW files for viewing. Some software only shows the embedded JPEG preview image which is rather small.

 

[unpopular]

not to mention that all of those are really bad reasons to shoot raw...

 

[SCraig]

Okay this might be a really stupid question but I was thinking about uses of RAW files. Since the shutter is open longer, sometimes by several factors, does that mean the sensor is collecting more information over a longer period of time? Doesn't that mean the files should be larger? If not, what am I misunderstanding about RAW?

I understand your question and I understand your confusion, however there is really no way that long exposure in and of itself can cause an increase in the file size of a RAW file. You aren't saving each photon that hits the sensor over a period of time, you are only saving the net result of ALL the pixels that hit the sensor over time, or the light VALUE of each pixel of the sensor.

To over simplify, take one pixel on the sensor. During a 1/100 second exposure let's say that "Z" photons hit that sensor pixel. During a 1 second exposure, 100 x "Z" photons hit the sensor so it has a VALUE that is 100 times higher than during the 1/100 second exposure. Taking it farther, during a 10 second exposure you might have 10 x 100 x "Z" photons hitting that particular pixel so it might have a VALUE that is 10 x 100 x "Z" higher but it is STILL only one pixel on the sensor.

The RAW file (or JPEG or TIF or whatever format you choose) stores the VALUE of each pixel on the sensor and not the number of photons hitting each pixel over time. The number of pixels on the sensor is unchanged regardless of how long the shutter is open.

 

[unpopular]

RAW files also compress data non-destructivey using something similar to LZW which will compress adjacent values, plus an index. So if there are six contiguous values at 32, it will record [6,32] instead of [32],[32],[32],[32],[32],[32]. JPEG also compresses data according to variation in values.

This is why scenes with lot of texture will be larger one without. I'd imagine that noisy scenes are also larger, and longer exposures tend to be noisy due to thermal interference.

But i do not think that this alone is why long exposures take so long to write. It may just be that the camera is giving the sensor time to cool off.

 

[SCraig]

RAW files also compress data non-destructivey using something similar to LZW which will compress adjacent values, plus an index. So if there are six contiguous values at 32, it will record [6,32] instead of [32],[32],[32],[32],[32],[32]. JPEG also compresses data according to variation in values.

This is why scenes with lot of texture will be larger one without. I'd imagine that noisy scenes are also larger, and longer exposures tend to be noisy due to thermal interference.

But i do not think that this alone is why long exposures take so long to write. It may just be that the camera is giving the sensor time to cool off.

JPEG started out as a very "Lossy" format since at the time it came into popular use there were few applications that provided control over the compression ratio.

You are right in that most compression schemes look at adjacent pixels and if they are the same RGB color the encoder simply says "Repeat that xx times". At higher compression ratios it also compares how close the RGB value of a pixel is to the block it is storing. For example, if there is a string of pixels that are pure black (RGB 0,0,0) except for a few pixels that are only a couple of points off (say, RGB 5,0,0) it will say "That's close enough" and include them in the pure black string. The higher the compression ratio the more latitude the encoder has in determining whether or not a pixel (or block of pixels) can be stored with the same value as adjoining pixels. Once that is done there is obviously no way of recovering the original data.

 

[Buckster]

Try reading a little more carefully.

Try it yourself.

Okay this might be a really stupid question but I was thinking about uses of RAW files. Since the shutter is open longer, sometimes by several factors, does that mean the sensor is collecting more information over a longer period of time? Doesn't that mean the files should be larger? If not, what am I misunderstanding about RAW?

Again....... shooting in raw has - n o t h i n g - to do with the shutter speed.

Look at the title of the thread.

I could be wrong, but I took the question as one about long exposure photos taken in RAW, like night photos.

Depending on the scene, the longer the exposure, the more info will be found in the RAW file, so it will be larger. Example: Say you're shooting a night scene. If you underexpose it at 1 second, it will mostly be black. With very little detail or variation in the data - just black everywhere, the file size will be smaller than if you expose longer, say 20 seconds, and produce a photo with much more details visible and available. However, if you expose even longer, so that everything's overexposed and white, the files size would again reduce because detail and variation has been lost again, and most of the image is white.

Here's another example to consider: Suppose you're shooting a black background and nothing else, in the in the pitch black dark. At 1 second, you get all black, and at 30 seconds you get all black - no difference in what you actually produce as a photo. No difference in detail - there is none - just a black picture. In that case, the file size would be relatively unchanged, no matter the shutter time difference.

 

[SCraig]

Depending on the scene, the longer the exposure, the more info will be found in the RAW file, so it will be larger. Example: Say you're shooting a night scene. If you underexpose it at 1 second, it will mostly be black. With very little detail or variation in the data - just black everywhere, the file size will be smaller than if you expose longer, say 20 seconds, and produce a photo with much more details visible and available. However, if you expose even longer, so that everything's overexposed and white, the files size would again reduce because detail and variation has been lost again, and most of the image is white.

Here's another example to consider: Suppose you're shooting a black background and nothing else, in the in the pitch black dark. At 1 second, you get all black, and at 30 seconds you get all black - no difference in what you actually produce as a photo. No difference in detail - there is none - just a black picture. In that case, the file size would be relatively unchanged, no matter the shutter time difference.

That's a good point, and it would affect the size of the file. It has nothing to do with the actual time involved though, it's simply the fact that the varying levels of luminance and chromanance affected the compression engine. As you said, anything with pure white or pure black (RGB 255,255,255 or RGB 0,0,0) will produce the smallest file size possible, and anything with varying tones in the data will increase the size of that file.

Looking at it in that respect, and assuming that longer exposure will cause a random (or patterned) change in the illumination values of the sensor's pixels (and a possible chromanace change in the filter's values), it is true that the file size would increase. Again though, it doesn't have anything to do with the time involved, only the fact that the values of the pixels of the sensor changed from pure black (or white) to alternating values that affected the compression within the file. The same could have happened by changing the exposure by 1/100 of a second which doesn't qualify as a "Long Exposure".

 

[unpopular]

This is kind of what I was trying to get at. OTOH though if the scene is very low in contrast the variation in file size would be minimized. Also because of gamma compression and poor low intensity performance, over exposed images tend to be larger than under exposed images. Looking at my RAW files i have one bracketed series I was trying to nail the maximum exposure over several stops with files ranging from 16mb to nearly 25mb with the largest file having blown highlights on all but the red channel.

but as you said, this isn't a function of exposure but rather the amount of detail.

 

[impulsive1]

not to mention that all of those are really bad reasons to shoot raw...

That's a bit subjective.

 

[KmH]

I guess the way I thought about it was, the sensor collects data at a rate of Xmb/s if you leave the shutter open for say 4 seconds compared to 1/60 of a second because of the rate at which the sensor gathers the data.

How Do I Use My Digital SLR?: What is a pixel, and how does it work?

Each pixel developes a voltage proportional to the amount of light that hits it during the exposure. That's all a pixel can do, record luminosity. The pixel doesn't record what color the light is. The voltage the pixel developes is analog.

The voltages are converted to either a 12 bit or 14 bit digital value, so computers can understand them.

The digital numbers have to be run through a conversion process that outputs an image approximating what a human can see. The image sensor doesn't work like the human eye does.

Here is an approximation of a Raw image file before and after conversion in a Raw converter:

Before:

After:

 

[480sparky]

I could be wrong, but I took the question as one about long exposure photos taken in RAW, like night photos.

I took it to mean this:

Set your camera up on a tripod in your back yard this afternoon and take a shot of it. Let's say the exposure is 1/60 at f/8. Now, wait until the moon is up tonight and take the same shot..... say, 30 sec at f/4. Nothing has changed other than the amount of ambient light. All you are doing is adjusting the camera settings to produce a properly exposed image.

Will the raw file of the night image be substantially larger that the daytime image simply because it's a 'long' exposure?

I can see where a cityscape taken during daylight hours would produce a larger file because you are recording all the details of the buildings, trees, bridges, etc., compared to a night-time shot where they are black (0:0:0) and you expose for the streetlights & neon signs.