PLEASE tell me I did not mess up!!!

Hi all, I was shooting my family pics over Thanksgiving and am just now getting them printed, planned on going to Longs at lunch. Much to my horror, I think I made a big mistake.

Since these were just family shoots and I only had a 125 MB card, I changed the pixel dimentions from the 8MP to about a 4MP ( I have a 20D). Well, since I hate flash and wanted to capture the mood, I dialed the ISO up to 800 or 1600. BUT I completly forgot to change the pixel dimentions back to the 8MP when I did this!! Isnt this going to cause huge gain/pixelation??

I made the ISO mistake last year, I was using a G3...but the image will have the same pixel demintions as my 20D( at 4MP), wont it??

Please tell me I did not ruin yet another batch of Thanksgiving pics......The sensor if differnet right??? RIGHT?????

I know the only way to find out is to get them printed, but I dont want to waste the money if they are going to be crappy and I dont have time to get a few printed today and then go back tomorrow and get the rest done if they are OK....

at 800 they might be usable, at 1600 you're risking it, it all depends on how much ambient light there is. the 20D is capable of getting good images at 1600, but you need light.

I have seen that the 20D is able to get good quality at 800ISO, but would this change if I changed the pixel dimentions??? Like I said, I was using the camera at about equiv, to a 4MP camera..

Shouldnt change by just changing pixel dimensions, remember a lot of people have use the 4mp 1D for high ISO shots. However, if you changed the jpeg QUALITY, or basically the compression, you could run into artifacting. Dont think pixelization will be a problem, but you could get blotchy colors or noise if you have it set on high compression (low quality).

You are correct in your assumption R2,

By using a smaller file size jpeg ... more importantly a lower resolution,.. the noise does become more noticeable as the "signal to noise" ratio gets worse.. ie.. the amount and size of the noise grain becomes larger relative to the rest of the image information.

This difference is not readily visible on screen iin a 100% crop.. but rather shows itself in print,.. or with a scaled image on screen. (scaled down to fit the screen size)

As to what degree this effect will have,.. and how useable the images will be,.. I don't think any of us could predict.. only you will know whaen you see them.

Thanks VW!! I hope you are right. My heart seriously stopped for sec. I think I kept the compression on low....Gees, now I am second guessing myself....AHHHH

Well, I think it is the more MP (of course this is not taking into consideration sensor size!!) the more quality you will get, with more MP, the more you can play with it and still rendor a decent pic (regardless of print size). At an ISO of 800, you will get better quality using a 8MP image, vs a 4 MP image. AT least this is what is in my head...Maybe that is wrong..

I don't think it's wrong... I agree.. at least as far as the perception of the noise is concerned...

My questiuon is why are you editing original files? And why on the CF? As part of your workflow, always copy your photos to your computer and edit ONLY copies, never originals.

noise comes from the sensor. if you are scaling the img down from the native 8mp to 4mp, noise will actually be reduced as the pixels are merged together.

you will have a 4mp image. a 100% crop will show less noise than an 8mp image, but it will of course have less detail.

try it in photoshop ... file .. new .. 100x100 pixels; filters ... noise ... add noise .. 20%; image ... duplicate; image .. image size .. 50%;

compare these two images -- there is less detail overall in the 2nd, including noise detail. if scaled back up to original size, the noise will look "chunkier" and technically there is less of it.

Um...I not editing anything...and I am not doing anything with the CF....all I did was change the pixel dim. because I needed a smalled file size. If I kept it at the 8MP level, I would not have gotten that many pics on my CF card. THat is why I changed the dim. in order to reduse the file size of each pic.

Thanks I will try this when I get home.

I agree with this.. if you are starting with an 8MP file and scaling it down..

This is what I am saying.. the more MP you have in the original image, the less noticeable noise is in the final print.

My understanding was that the original images are not 8MP... rather with the camera set to a lower res at the time of taking the image. So the orginal files are only 4MP.

The question then becomes,.. by setting the camera to take a reduced res jpeg,

...are you getting an image file that is essentially an 8MP file that is interpolated DOWN to 4 MP?... (in which case noise would be LESS perceptible)

...or are you getting an image file like those of a 4MP camera? (in which case the images would display noise MORE)

Is my logic on this making any sense?

I suppose by now I should now what the effects of setting an 8MP camera to take a 4MP image are... but I've never had reason to look it up as I'd never do that.

Okay then, manipulate, change, resize, change "pixel dim." etc, etc. Never do that to original files.

Exactly- well, i guess we will al know once I get off of work. I dont normally do this (making the file 4MP)- but a 125 MB Cf card will only take you so far, calls for drastic measures....But I have just purchased a larger card, so I wont have to do THAT again...
And besides, it was just family shots, I just got the camera 4 days earlier, there were many cameras taking the sme thing I was, so if they dont turn out, it wont be a total loss...:}