Jump to content

Recommended Posts

Hello,


 


I would like your advice please if I may.  I notice that the minimum file size you are requiring is 25 meg.


 

I use two cameras; 1) Canon eos 50d and 2) eos 5d mark 3 and shoot both in raw and jpeg maximum quality at the same time (per camera). 


Jpeg file sizes are nowhere near 25 meg when saved but raw files are more than 25 meg most of the time. 


 


My question is can you please advice me as to how do I produce jpeg files over 25 meg?


 


Many thanks,


 


Cozmic Dave


Link to post
Share on other sites

Coszmic Dave,

You need to read the submission text carefully.  The 25 meg size requirement refers to the file size that results when you open the jpeg, not the jpeg file size.

Link to post
Share on other sites

It's just a roundabout way of saying 8.4 (approx) MP

 

Each pixel needs 8 bits per channel for Red, Green, Blue so 3 Bytes per pxel

 

3 * 8,400,000 = 25,200,000

 

(25,200,000 / 1024) / 1024 = 24.03 MB

Edited by woody
Link to post
Share on other sites

With a 5D III the file size is almost 60MB, not 18MB, that's a typical largest (most detailed) JPEG compressed size (Alamy may reject compressed images over 25MB, or over certain pixel dimensions, and I've had to reduce two or three of my largest panoramas for this reason). Any camera marked as being 9 megapixels or more will produce Alamy size images if you do not resize or crop them, and any camera producing images larger than 9 megapixels allows you to crop down to as small as 9 megapixels. The safe size for reducing or cropping a 35mm shape 2:3 format is 2400 x 3600 pixels or 8.6 megapixels - it gives you 24.2MB, just .2MB above Alamy's minimum.

Link to post
Share on other sites

Cozmic, I think what makes this confusing for many people is that the term "file size" is used in different ways. The Alamy requirement of at least 25 Mb is sometimes referred to as the "image size", and that's how I'll refer to it here.

 

When you open an image in your photo software, it has an "image size", which as David Kilpatrick points out, is determined purely by the pixel dimensions. If you take two photos at the same resolution with the same camera, they will always have the same image size.

 

"Image size" can be found in various places in various software (but usually called "file size").

 

What some people (like me, coming from an IT background) automatically think of as "file size" is output file size:

 

- the size of an 8-bit tiff output file is the same as the image size

- the size of an 8-bit compressed jpeg file varies, depending on the level of compression and the content of the image

 

but Alamy is concerned with the "image size."

 

They do also have an upper bound on the output jpeg file size, but I can't find the specific reference at the moment.

 

And as David also points out, you quickly know what image sizes your cameras produce and don't worry about it thereafter, unless you're doing a big crop.

Edited by Bill Kuta
  • Upvote 1
Link to post
Share on other sites

It's an incredibly confusing topic for many people. Endless confusion arises between the pixel dimensions of the image and the file size on disk.

They do also have an upper bound on the output jpeg file size, but I can't find the specific reference at the moment.

 

The maximum pixel size (as revealed by the Image Size dialog in Photoshop for example) is 200 Mb. Minimum pixel size is 24 Mb. Alamy refer to this as the uncompressed file size. I would reword this as the image or pixel size.

 

Link below has the Alamy info.

 

http://www.alamy.com/contributor/help/image-submission-checklist.asp

Edited by MDM
Link to post
Share on other sites

Everyone understands image dimensions, not everyone understands the difference between an image size in RAM and on disk.  It would be far simpler to state the min requirement in MP like the rest of the world does.

Link to post
Share on other sites

Everyone understands image dimensions, not everyone understands the difference between an image size in RAM and on disk.  It would be far simpler to state the min requirement in MP like the rest of the world does.

Yes and no or maybe or maybe not. Megapixels have used since the advent of digital cameras and this is one of the quantities available as a readout in Lightroom. But scanned images were always given by Photoshop in pixel size (3 X MP as stated above).  The pixel size and file size on disk for uncompressed, flattened psd or tiff files are pretty much the same. The confusion arises because there is no proportional relationship for JPEG, as the degree of compression and the resulting file size will depend on the content of the image. Files with lots of detail will have a large size on disk and files with lots of similar areas such as sky will be more compressible and therefore smaller.

 

In reality, it's not that difficult. It just needs to be clarified somewhere in plain and consistent English, with reference to the most popular apps that people use to process their files. Then all that should be required is that people read the guidance.

Link to post
Share on other sites

Funny, I never had a problem understanding Alamy's minimum file size requirement. It's just the size of the file before you compress it (in the case of an 8-bit TIF) or after you uncompress it (in the case of a JPEG). Perhaps being a non-techie actually helped me in this regard as I didn't know enough (and still don't) to complicate the matter.

Link to post
Share on other sites

Funny, I never had a problem understanding Alamy's minimum file size requirement. It's just the size of the file before you compress it (in the case of an 8-bit TIF) or after you uncompress it (in the case of a JPEG). Perhaps being a non-techie actually helped me in this regard as I didn't know enough (and still don't) to complicate the matter.

You are probably more of a techie than you give yourself credit for John. Using terms like 8-bit TIF gives you basic techie grade at least.

  • Upvote 1
Link to post
Share on other sites

 

Funny, I never had a problem understanding Alamy's minimum file size requirement. It's just the size of the file before you compress it (in the case of an 8-bit TIF) or after you uncompress it (in the case of a JPEG). Perhaps being a non-techie actually helped me in this regard as I didn't know enough (and still don't) to complicate the matter.

You are probably more of a techie than you give yourself credit for John. Using terms like 8-bit TIF gives you basic techie grade at least.

Thanks, I try to be only as much of a techie as I need to be. No point in overloading the brain cells IMO. :D

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.