图像分辨率的终极指南

你如何在Photoshop中实际做到这一切?

+$The 'Image Size…' dialogue in Photoshop – or similar apps – looks simple, but it's a minefield if you don't know what you're doing. The key thing to remember is that all the fields are essentially connected (because the pixel dimensions, resolution and physical printed size are). Changing one value will change others too, depending on what kind of resizing you're trying to do. Here's a guided tour.

单击右上角的图标可放大图像

+$Aspect Ratio (1)
+$This maintains the aspect ratio – the relationship between the width and the height. For almost every job you do, this should be active. Click to toggle.

+$Units Of Measurement (2)
您可以看到以像素,厘米或其他测量值显示的图像大小。请注意,当然所有内容仍然是相互关联的,因此如果您切换到厘米并更改值,则像素数也可能会发生变化。

+$DPI (3)
这是图像的DPI(或更确切地说,PPI;澄清......)。

+$Resample Option (4)
+$This is the tricky one. With this Resample option unchecked, the pixel dimensions (the number of pixels across and down) of your image won't change as you tweak the values. You're essentially just making each individual pixel bigger and smaller for output (as in Example A on the previous page) when you adjust the resolution or physical size. With this box checked, you're changing the pixel dimensions, either up or down. If you ultimately add more pixels (keep an eye on the Dimensions readout at the top), they'll be added using interpolation (Example C).

+$Resample Types (5)
您可以在此处选择如何重新采样图像;如果您不确定,请将其保留为自动。 “最近邻”是不使用插值的唯一选择,通常不应该使用它;一个常见的例外是,如果你正在处理像素完美的图形,如低分辨率的截图或像素艺术+$, and you want the detail not to get smeary when you boost or reduce the resolution. In this case, work in increments of 100%.

这应该有希望让你对DPI和决议的作用有一个基本的了解,但我敢打赌你还有问题。让我猜猜他们是什么,并尝试回答他们!

+$What DPI should my images be at for print?

对于打印,300dpi通常是最佳的,但你可以少花钱;甚至150dpi通常也适用于摄影图像,尽管它会开始看起来像徽标之类的垃圾。然而…

+$What DPI do I need for screen?

+$Most people are under the impression all images for screen should be at 72 or 96dpi. However, DPI is broadly irrelevant for designing images for screen, and not just because 'DPI' is specifically a print concern. Because you'll be presenting a grid of pixels (your image) slotted one by one into another grid of pixels (a screen), 'the size of the pixels', which is what we're talking about when we're talking about DPI, is irrelevant. So in general terms, you just need to care about the pixel dimensions, not the DPI/PPI.

72 / 96dpi的东西是传统的kludge,你可以大多忽略它,特别是今天的高分辨率显示器,它们在创建@ 2x版本时有自己的问题。

但是有一个问题:在某些情况下,系统可以尝试从元数据中读取DPI值,并且能够巧妙地了解它们如何呈现图像,当您只需要显示像素1:1时。所以,就像它让我烦恼一样,我有时会手动将目标为网页的图像分辨率设置为72dpi。

+$Why does my printer print at 4800dpi?

普通现代计算机屏幕上的每个像素都可以显示1680万种颜色中的一种,但是当该像素打印在喷墨打印机上时,除非它是纯青色,品红色,黄色或黑色,否则打印机必须重新创建它的颜色。通过在该像素的边界内放置更纯净的C,M,Y或K墨水点,使我们的眼睛将像素视为正确的颜色。

因此,打印机需要放置的每英寸实际点数必须很高 - 远高于您发送给它的大多数图像 - 以便您可以创建每个像素所需的颜色。这就是为什么像我早期做的那样将DPI,PPI和SPI混为一谈在技术上实际上是一个糟糕的主意。

然而,许多人只是将所有三个'DPI'称为 - 即使Photoshop在其对话框中正确地将其称为PPI - 除非您获得技术或迂腐,否则通常也可以。 (也有LPI,但不要让事情进一步复杂化。)

+$What is image 'resolution'?

+$At this point, you're probably wondering, when someone asks for the 'image resolution', if they're referring to the pixel dimensions or the DPI (or PPI)? Well, it can be either. Sorry. Different people use the term for each, and anyway it depends on context. If you're unsure, clarify.

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