Aspect Ratio is everything
Before we start, It helps to have the Cropped Dimensions showing on the Image Overlay. Press the letter I until the overlay appears.
Go to: View/View Options… and make sure Cropped Dimensions are showing somewhere, in either Info 1, or Info 2.
YouTube Video on Image Size on Export from Lightroom
Cropping to the Aspect Ratio of the size you want on Export
If you want an image to be a fixed size in pixels, inches, or centimetres; you have to crop to that Aspect Ratio in Lightroom. If you don’t crop to that Aspect Ratio, only one edge will be respected. The edge that will be respected will be the longest edge of the image. The other edge will be resized to match the Aspect Ratio of the size you want on export.
Let me explain.
If a landscape oriented image has a cropped size on the screen of 7000 x 5000, and you export with an image size of 1024 x 768. The exported image would have an image size of 1024 x 731. So, the longest edge has been respected.
If you want to have a fixed image size, let’s say 1024 pixels X 768 pixels – you have to crop to that Aspect Ratio. If you cannot work out the aspect ratio, just enter in “Enter Custom…“, the dimensions of the export image you require. On this occasion enter 1024 x 768. The 1024 x 768 is actually 4 x 3 Aspect Ratio, but let Lightroom do the work.
The process is:
Click on the drop down directly opposite “Aspect:”
Go to “Enter Custom…”
Enter the Dimensions of the size you want on export.
Don’t bother to calculate the lowest divisible number yourself, let Lightroom do the work.
Notice “4 x 3” is now in the Aspect box. Lightroom has done the work for us.
Notice also, the locked Padlock symbol, which ensures we can’t break the Aspect Ratio. All you have to do is move and resize the crop to your heart’s content, as long as the Padlock is locked. Once your happy, press return or “Close” the Crop Tool.
Exporting the File
Go to File/Export, or Shift Command/Control E, (Command on a Mac, Control on Windows PC).
We’ll ignore File Settings for now, and concentrate on Image Size.
Enter your dimensions into W & H.
Don’t Enlarge – well if you tick this it won’t enlarge (upscale) the image. There might be a rare occasion when you might need this.
If you select pixels, Resolution does not matter. Output at 1 PPI, if you want. PPI does not mean anything if pixels are used as the measurement scale. Put 72 PPI if it makes you happy.
The resolution, in this dialogue, has no effect when pixels are the selected. All that will happen is the PPI will be embedded as Metadata within the file.
The word resolution has more than one meaning
Unfortunately, the word resolution has many meanings. It can be expressed as “The amount of detail an image can hold”. Or, resolution can be just Pixel Dimensions.
In the export dialogue box in Lightroom – size is all that matters – even when going to print.
Changing the measurement scale from pixels to inches, or centimetres causes the Resolution PPI to kick in. Again Lightroom is not judging the quality of your image – size is everything.
When using 300 PPI, for example, all you are saying is give me the equivalent of 300 pixels one inch of paper.
PPI, and Printing
Let’s assume you want to send your file to an online printing bureau.
You’ve cropped to the aspect ratio you need. You’ve entered the dimensions in inches, or centimetres you want in the width, and height. Unfortunately, in Lightroom, you are not going to get any feedback on the screen. So, how do you know what size you are going to get at the current Cropped Dimensions? All you need to divide each Cropped Dimension edge by the Resolution PPI figure. For example, if both sides are 900 pixels x 900 pixels, and the Resolution PPI was 300, the math would be:
900 ÷ 300 = 3 inches
As the image is square you are going to get a 3 x 3-inch image at 300 PPI
The principle is simple: Divide the Width, and Height by the Resolution PPI to get the image size in inches, or centimetres. Using inches is prone to rounding errors, so there will be a small margin of error.
In the case of the 300 px x 300 px image at 300 PPI, using any size different to 3 x 3 inches will result in image resizing.
The resizing processing is called Interpolation, which cannot be controlled in Lightroom – but it can in Photoshop. Don’t forget, that making an image larger, or smaller results in some loss of quality – however small.
You can control the image size by changing the Resolution PPI, but it’s not the normal way to do things. I suggest you print at whatever your printer manual or Print Bureau recommends, and change the dimensions only
By the way, Dots per Inch is totally meaningless in the context of Lightroom, or Photoshop. A dot is a dot, a pixel is a pixel. How many dots it takes to make represent a pixel on paper, varies between printers.
Exporting for an Online Print Bureau
Good print bureaus will ask for:
- JPEG or TIFF 8 bit flattened, and with no compression. Personally, I would use TIFF, over JPEG. If you have to use JPG go for maximum quality, why take the risk of lower quality settings.
- There will be file size limits which are hard to break. If you break the file size with TIFF, consider JPEG. If you still break the file size limit with JPEG, use Limit File Size.
- Ideally, the image has been Soft Proofed using the print bureaus downloadable Colour Profile for your chosen paper. Use the correct profile in File Settings/Color Space, in the Export Dialogue box. If you can’t be bothered to Soft Proof, use Adobe RGB 1998. Important: If you have not profiled your monitor, you are likely to get back a lemon from the bureau. I have done a video on Soft Proofing which is here
- Sharpen for the paper being used. Standard works for me. Only eyeballing the returned print well show how the sharpening has worked. Over Sharpen in the Detail Panel in the Develop Module. There are plenty of articles on the web about sharpening for print.
If you are exporting to another screen but not the web, let’s say another photographer, just ask what they want. Most digital image professionals would prefer an uncompressed TIFF at 16 bit. TIFF’s make for large files, especially at 16 bit uncompressed. Most email providers will not allow attachments larger than 25mb, so FTP might have to be an option or a cloud service like Dropbox.
If you are going out the Web especially your own website, or you are doing work for a Web Designer who wants you to prepare the images, then the next article will apply.
Exporting for the Web (Screen)
- JPEG only. The higher the quality, the bigger the file size. Seventy is seen as a safe setting. If you are outputting to your own website or handing your work over to a Web Designer, for instance, lower the JPEG quality until there is little discernible difference between the original and your exported JPEG. These quality decisions are important for everything except Social Media websites, like Facebook. Since the dawn of the Web, slow loading sites are a big no-no and will be punished by Google in the site rankings. Incidentally, most Social Media sites compress the hell out of your JPEG anyway, so leave the quality at seventy, it’ll be fine. There’s a very good article by Jeffrey Friedl about JPEG quality on Export which can be accessed here. Also, Jeffrey has an excellent Lightroom Plugin which allows you to export one image as twelve different JPEG’s at different quality settings, plus one lossless TIFF, this plugin can be accessed here.
- Colour Space: sRGB (Screen, Red, Green & Blue), is the safest bet. Some web browsers can read colour spaces, but more importantly, all screens support sRGB. Some browsers even support Adobe RGB 1998. Most punters do not have a colour profiled screen so it’s like the Wild West on the web. Stick with sRGB to be safe.
- Sharpen for Screen Standard – this works for me. It is important to sharpen on export, as most of the time you will be resizing the image.
- Make sure you have ‘Cropped Dimensions’ showing on your Info Overlay
- Crop to the Aspect Ratio of the Image size you want on export.
- If you untick Resize to Fit or use pixels as the measurement system – Resolution PPI will not matter.
- When using inches, or centimetres. Divide the Image cropped dimensions by the PPI, to get an approximate size in inches, or centimetres. Any size changes in inches or centimetres away from this figure will result in resizing (Interpolation)
- Go for the lowest quality setting, without too much loss of quality when using JPEG for outputting to your own website, or you doing work for a Web Designer. I’ve gone as low as 20 quality settings on some photos. For Social Media sites 70, or even 60 will be fine, as they compress the image as well.
- Don’t forget to sharpen on export – Standard works well.