File size of saved photos

[Eggle]

I have been taking lots of photos today, some in auto setting and some in program. All set at max file size, least compression and have downloaded them to the pc. Sone of them in jpeg are 3.5Mb in size but some of them are say 886Kb. This seems a very small file and I would have expected them all to be very close in file size. I don't want to go RAW as I don't want the post prosessing.
Camera is a Canon 20D
is this normal practice for this type of camera?

[grumbledoak]

Jpeg is compressed, so yes this is normal.

[Simpo Two]

The 20D is 8.2Mp, so from my experience with a 6Mp D70 I'd expect best quality JPGs to be 3-4Mb. So 3.5Mb sounds good but 886Kb is defo wrong. Sure you haven't tried changing the compression/image size as well?

[crmcatee]

I seem to recall you can set the quality of images differently on Auto and Program. Sounds like one of them may be set to capture the JPG as JPG-Small. whilst the other is set to be JPG - Large.

[Lambochick]

crmcatee said:

I seem to recall you can set the quality of images differently on Auto and Program. Sounds like one of them may be set to capture the JPG as JPG-Small. whilst the other is set to be JPG - Large.

I think that sounds to be the problem. Easiest way to check is to look at the pixel dimensions of the actual images. A jpg small image will be quite a bit smaller in width and height than one captured at a higher setting.

[Eggle]

So so confusing. I thought I had set the quality once and for all. It seems as suggested the auto setting was set on high q, low comp. The program setting was set on medium. Thanks guys.

[S. Gonzales Esq.]

Perhaps not the case here, but the size of a file can be hugely affected by what the pictures are of. Jpegs work by averaging adjacent pixels to reduce the amount of data, so if the images already contain large areas of similar colours then the resulting files will be smaller.

Edited by S. Gonzales Esq. on Sunday 18th April 22:01

[Simpo Two]

Eggle said:

I thought I had set the quality once and for all. It seems as suggested the auto setting was set on high q, low comp. The program setting was set on medium.

A good reason not to use Auto - the camera does things you don't know about until it's too late.

S. Gonzales Esq. said:

Jpegs work by averaging adjacent pixels to reduce the amount of data, so if the images already contain large areas of similar colours then the resulting files will be smaller.

They will be, but not by that much. From a 10Mp sensor I find that JPGs can be between 4Mb and 9Mb depending on detail - but not 800Kb, which as the OP rightly spotted, isn't right.

[itsnotarace]

Simpo Two said:

They will be, but not by that much. From a 10Mp sensor I find that JPGs can be between 4Mb and 9Mb depending on detail - but not 800Kb, which as the OP rightly spotted, isn't right.

Disagree - as the person you quoted pointed out it depends on the subject. I have a whole bunch of lunar eclipse shots from 2007 taken with a D200 at 3872x2592 and they average 300kb. The NEF files were 6.4Mb in size and the jpegs were 264kb at the lowest value, most were between 288 - 300 and the largest 500kb.

[Simpo Two]

Well let's solve the issue by asking the OP the subject of his 800Kb image (or posting it).

[Eggle]

OK, I will post the extremes. I was guessing the file sizes for the purpose of the post.
In Medium, the files range from 606Kb to 1,144Kb.
In High, they range from 2,548Kb to 5,005Kb
And look like these...
606KB
1,144KB
2,548KB
5,005KB

[scorp]

Simpo Two said:

They will be, but not by that much. From a 10Mp sensor I find that JPGs can be between 4Mb and 9Mb depending on detail - but not 800Kb, which as the OP rightly spotted, isn't right.

Jpeg works by breaking the image into frequency components and then removing* frequencies which are barely noticable (depending on 'quality'/'compression' settings). If your picture if very blurry it will have no high frequency components thus making encoded output a lot smaller. I notice in the examples above the larger file sizes have a lot of fine (high frequency) detail and the smaller ones are more blurry.

• usually it reduces the resolution of frequencies rather than removing them completely which causes the ringing artefacts in aggressively compressed JPEG.

Edited by scorp on Monday 19th April 10:49

[Simpo Two]

Eggle said:

In Medium, the files range from 606Kb to 1,144Kb.

Well that's your answer - they were taken at 'medium' (though we're not sure whether that's medium size or medium compression, or perhaps both). Case closed