DOES THIS MAKE SENSE? image resolution and scaling...?

Question

Hi, I have to write about image resolution and scaling for my photography/digital manipulation essay at university, but to be honest am a bit confused! Can you please read through this and let me know if it makes sense and is correct? or if anything needs changing? THANK YOU!

---

It was then time to plan and take my images. I made sure I took them in the highest possible resolution on my camera and in fine JPEG format, so they would be the best quality possible. A higher resolution means finer detail is shown in the image, and the better the printed image will be. This is important for this task especially, as the prints need to be of magazine standard and I can not afford to damage or lose any image quality along the way. Using a lower resolution would save memory space on the camera but would result in a more pixelated appearance of the image and a much lower quality. Changing resolution changes size at the same time (as resolution is pixels per inch, therefore a higher resolution uses more pixels and takes up more inches). This is also important as a larger image eliminates the need for scaling to enlarge it to magazine size. Scaling stretches the pixels over a greater area, so the quality is damaged badly (the image appears more grainy and pixelated) and cannot be repaired at the scaled size. Scaling up is never something I would recommend - just take the picture at the largest size you can and eliminate the need. Scaling down doesn’t damage quality so you can always do that if it’s too large for your purpose, rather than stretching and deforming the image (both on screen and in print) to make it bigger. This is what people often do for web pages - take large images then scale down to preserve the quality to a good extent. Image editing programs do use a process called ‘sampling’ when scaling up to try and minimise the damage to the image, but it will never be perfect or as good as it could be. Scaling is always going to cause some degree of damage, therefore is never an ideal option.

---

I was meant to evaluate the effects of resolution and scaling too, and evaluate the use of scaling to 'enlarge, reduce or reproduce size'... no idea if I've done this or not!!!!!

Answer 1

In general, this is correct. Most professional web page makers, use a scaled down 'thumbnail' version of the larger image which is joined to the larger image by a clickable hyperlink. If they used a scaled image on the web page it would take longer to laod then a scaled down thumbnail.



If using image types (such as jpeg - jpg, img, png, bmp) some of these actually compress the data and can cause data image quality loss. Jpg for example is a quality loss compression technique. Bmp (Bitmap) loses less quality and Png (Portable Network Graphic) stores the image in a format that enables not only lossless scaling, but even image layering. It was hoped that Png would be adopted as the web standard instead of Gif and Jpg, but it hasn't quite caught on.

Answer 2

What you have written is basically correct. I just want to add something to deonejuan's answer...



If you want to edit a JPEG file and need to use Save or SaveAs repeatedly (like he said this can degrade the quality if you do this enough times). So the *solution is to save the JPEG as a TIFF file for purposes of editing. Once you have finished editing it you can then save the TIFF back to a high quality JPEG and discard the temporary TIFF file.



You should also mention that if you scale down the image (e.g. for display on the web) then you should always keep a copy of the original full size JPEG. Like you said you need all those pixels for high quality prints so you don't want to throw them out.



You are also right to say that finest quality JPEG is of a very high and professional standard (and yes I know I'm being controversial now). Some people will say that RAW is the finest quality for digital images. And this is true. But the proof is in the pudding. I have actually compared fine quality JPEG with RAW side by side and there is literally no difference. Well there may be some very slight difference, but I could see no signs that the difference represented a degradation in quality. For all I knew the JPEG's so called 'degradation' could in fact have been an improvement! And that is a fact!



So back to your question - I think you've basically got it right. Especially you seem to understand that the resolution is measured by the 'total amount of pixels in an image'. And more pixels equals finer quality prints. You also mentioned the problem with down-scaling an image.. that you lose pixels that cannot be regained by up-scaling.





---

*I've also read that if you save a JPEG as a copy, then edit, and finally save -- that this will eliminate the degradation of the JPEG caused by multiple saves (and you would have to do this for each session that you wanted to edit the JPEG). This could well be true but I can't recommend it as I haven't tested it. I also think it is simpler to just save as a tiff for editing. I have no idea which method gives better results.

Answer 3

JPEG is a lossy format. Every time we Open and Save or SaveAs... will activate the JPEG engine to optimize the pixels. In JPEG format if the engine finds three pixels of R x R, the optimization algorithm might convert that to R R R. In binary on the hard drive that becomes 3R. OK we lost a subtle shading on that pass, but the 3R is a glob that can now look like:

3R x B R 15R

Several edits could make the glob consolidate into

21R



That is an overly-simplified illustration of the JPEG algorithm, but it really does happen that way. 15 edits and we will notice details are fading. Keep that in mind.



Also, when we scale, when we go down, the algo is to discard. Visualize a screen window and a tennis racket screen. The racket mesh has 1cm squares full of pixels. The algo will approximate the same glob into the window screen sized mesh and discard. We still might not have the web page resolution when we do scale. Your 12.1 megapixel might be 900 dpi originally, the scale has made dpi 188. Open that scaled in a web page and it is not the photo size we expected. Web pages display at 72dpi. So...



We resample the scaled. It takes a photo program like GIMP or Photoshop. You set print size. Keep the photo dimension at your desired width and height and change dpi to 72. Next view on the web page will be what you expected.



Now, for magazines. In general, 300dpi resampled at dim size for ordinary quality so we can fit the photo on a CD. The printing company will let you know those particulars.



Now, to go up. If we have a web page of 72dpi and we want to make a poster. That takes software to gain the mixed results. The pixels are missing that would fill in the blank spots. Do you understand?



Hope I helped. I'm an ex-graphic artist.

Answer 4

its based on the projector and the image resolution. higher resolution means more clarity and better details but if you projector is a poor quality projector it wont matter much. your images should be fine.