Screen resolution question

I have a very ignorant question regarding the resolution of screens and the resolution of images.

Suppose I have two laptops with different screen resolution, say A has lower resolution, B has higher.

If I plug my external web cam into one of the laptops to take pictures, then edit the pictures using a photo editing software, will the different resolutions of the laptop A and B make difference to the resolution of the resulting images? In other words, does it make difference which laptop I use to take the pictures?

Very ignorant indeed, thanks for your patience

 

your web cam, when taking a picture, will record the image to a file(i.e. 800x600 pixels)

then you edit it with a software... as long as you save the pic without changing the dimensions, or resolution(eg 50ppi), or compress the image(eg saving to a black&white 6-bit image), it'll be fine

 

Thanks. I found that if I open the image file with the photo editing software, then re-save it as jpg file (it was jpg originally also), even if not doing any editing, the resolution reduced a lot. Is there a way to keep the original resolution?

 

If you're using something like photoshop, it shoudln't alter the resolution. Most photo editing programs shoudlnt' alter the resolution if you open the file directly and save it.

 

I use Adobe photo deluxe. If I choose to save as gif file, then the original resolution is preserved, but if save as jpg file, then the resolution is reduced a lot: original 400KB image becomes about 70~80KB! But the gif version doesn't seem to be clearer?

 

gif and jpg are lossy formats... they discard information depending on what settings you use...

if you want no loss of data, save it to the program's default file format (eg in photoshop, save it to .psd)

if you save to jpg, look at the dialog... there should be options for you to control the compression and quality ratios

p.s.: PNG > JPG

png is (i think) lossless, while for jpg it is lossy... everytime you save something to jpg, you lose data... everytime you save to png, you retain the quality

 

Yup, you're right; hencewhy PNG's are able to retain any transparent backgrounds while JPEG's turn them into white backgrounds; a JPEG is similar to taking a screen-shot of a screenshot, not eveyrthing can be preserved at top quality in the exact same way the original pic looks.

But in terms of the resolution thing, i have no idea why the resolution would get all messed up if you just saved it as a different output

 

I think he is confusing resolution with straight file size. JPG is a compressed format, and most programs will let you set the compression settings. For the vast majority of uses, a middle quality JPG is more than sufficient, lossy or not. And you aren't losing any resolution, only pixel fidelity. One of the major benefits of JPG is that you cut your file sizes down by 50%=90% compared to other formats. That's why JPGs are so prevailant on the web.

 

Actually Sirmetman may be right; After re-reading the OP's response, it looks like he's just getting bewildered by the difference in file sizes

 

Yes, you are right! I thought the reduced file size means reduced resolution. Reading your replies, it seems this is not so? However, I saved the same image in GIF and also in JPG; the result: the GIF image looks more grainy, while the JPG image looks more smooth. What does that mean? And, if resolution is not lost, what is lost with the reduction of file size?

Thank you all for being so kind and patient with me

 

Image quality. The GIF image is grainy because it loses some of the picture data when it's saved in that format. JPEG has a higher quality, and thus a bigger filesize, although it still loses some quality. A PNG image will not lose quality, and will have a larger file size. And a 24-bit BMP will be the highest-quality and largest of all.

 

But the GIF file has retained the original file size, more than 400kb, and the JPG file has only size 70-80kb. I thought the JPG should be more grainy??

 

I forget the exact compression methods that JPEGs use, but basically, they play mathematical games with the color values across fields of pixels to reduce the size of the file. These games reduce the picture quality some, but they don't reduce the resolution. For a simple example of how compression can reduce file size, imagine an image that contains a large red square. In something like a bitmap, each pixel within that square will have a full 32 bit value for it's color, even though they are all exactly the same. There are a number of ways to compress this, but one way would be to define the entire block of red pixels by the coordinates of its corners and the color. This isn't exactly what JPEG does, but it should give you an idea of how compression can reduce file size without reducing resolution.

 

If you save to a jpeg make sure you set the slider to the highest quality...this dialog appears when you choose "save" If your webcam takes a jpeg picture it shouldn't get smaller after editing it in photoshop.