Photo quality and resolution

[garfield]

Things were simpler in the 35mm SLR age:
I had the given ISO and I made the exposure ajustments according to the given light situation.

Now I can change the ISO as I see fit (which is great)
But I haven't fully understood the function and relationship between:

ISO, Megapixles(resolution) and Compression.

How do they work and how do they effect the overall
exposure?

Can anyone help?

[atkinson1]

You are really looking for some basic digital camera information, to set things straight.

From http://steves-digicams.com/digi_dictionary.html:
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ISO - The speed or specific light-sensitivity of a camera is rated by ISO numbers such as 100, 400, etc. The higher the number, the more sensitive it is to light. As with film, the higher speeds usually induce more electronic noise so the image gets grainier. ISO is the abbreviation for International Standards Organization. (In the good old days it was known as the "ASA film speed.")

Megapixel - CCD resolution of one million pixels. Digicams are commonly rated by Megapixels. You multiply the horizontal resolution by the vertical resolution to get the total pixel count:

1280 x 960 pixels = 1 Megapixel
1600 x 1200 pixels = 2 Megapixels
2048 x 1536 pixels = 3 Megapixels
2272 x 1704 pixels = 4 Megapixels
2560 x 1920 pixels = 5 Megapixels ... and so on
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ME: If a camera CCD has more megapixels, the image can be printed larger. Film is the equivilent of about 20 MP, because it can be enlarged to huge poster sizes and still maintain a good quality and detail.

2 MP will print a photo realistic picture at 6x4 inches. 3MP up to 8x10 inches. And so on. Very Professional Cameras go as high as about 16-20MP, but cost tens of thousands.

Compression is when the camera stores images at a much smaller file size. Here's what 'stopbath' posted about some compression in files:

"TIFF and other lossless formats like PNG will compress the file by using exact calculations. These files will decompress to exactly the same quality as the original. A file saved 100 times will remain an exact copy of the first version.

Jpeg compresses by approximating. Given the level of compression and options, it will start approximating the photo into little blocks of data. At each save the file will be re-approximated. So if you save the file 100 times, the file will be re-evaluated 100 times. The resulting file will be of lower quality than the first.

Therefore, never save as jpeg until you need to. Try to always use TIFF, PNG or some other lossless format for every save you make during your edit process. Try to never edit the original camera file. Make a dup first for any editing."


- Hope this helps.

[garfield]

atkinson1

Thanks for the reply.
The information you provided is valuable.

I am getting used to the camera, the A70 is a fantastic one, but I still miss holding my SLR, (Canon Rebel) Its large viewfinder, the focusing and zooming of the lens...